JP4222292B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery including a wound body obtained by laminating and winding a positive electrode and a negative electrode with an electrolyte interposed therebetween, and in particular, can absorb and release an electrode reactant, and constitutes a constituent element. The present invention relates to a secondary battery including a negative electrode including a negative electrode active material including at least one of a metal element and a metalloid element.

  In recent years, many portable electronic devices such as a camera-integrated VTR (video tape recorder), a mobile phone, or a notebook 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.

  As a negative electrode active material used for a lithium ion secondary battery, a carbon-based material such as non-graphitizable carbon or graphite having a relatively high capacity and good cycle characteristics is widely used. However, considering the recent demand for higher capacity, further increase in capacity of carbon-based materials has become an issue.

  From such a background, a technique for achieving a high capacity with a carbon-based material by selecting a carbonization raw material and preparation conditions has been developed (see, for example, Patent Document 1). However, when such a carbon-based material is used, the negative electrode discharge potential is 0.8 V to 1.0 V with respect to lithium, and the battery discharge voltage when the battery is configured becomes low. Then we cannot expect a big improvement. Furthermore, there is a drawback that the charge / discharge curve has a large hysteresis and the energy efficiency in each charge / discharge cycle is low.

On the other hand, as a high-capacity negative electrode that exceeds carbon-based materials, research is being conducted on an alloy material that applies that a certain type of metallic lithium is alloyed electrochemically and is reversibly generated and decomposed. For example, a high-capacity negative electrode using a Li—Al alloy has been developed, and further, a high-capacity negative electrode made of a Li—Si alloy has been developed (for example, see Patent Document 2). An intermetallic compound called Cu ₆ Sn ₅ has also been developed (see, for example, Patent Document 3).
Di. D. Larcher, “Journal of The Electrochemical Society”, 2000, Vol. 147, p. 1658-1662 JP-A-8-315825 US Pat. No. 4,950,566, etc. JP-A-6-325765 JP-A-7-230800 JP 7-288130 A JP-A-5-234620 JP-A-11-260415

However, Li—Al alloy, Si alloy, or Cu ₆ Sn ₅ expands and contracts with charge / discharge, and pulverizes every time charge / discharge is repeated. Therefore, there is a big problem that cycle characteristics are extremely poor.

Therefore, as a technique for improving the cycle characteristics, it has been studied to replace a part with an element that does not participate in expansion / contraction due to insertion / extraction of lithium. For example, LiSi _s O _t (0 ≦ s, 0 <t <2), Li _u Si _1-v M _v O _w (M represents a metal excluding an alkali metal or a similar metal excluding silicon, and 0 ≦ u, 0 <v <1, 0 <w <2), Or the LiAgTe type-alloy is proposed (for example, refer patent documents 4-6). However, even with these negative electrode active materials, the fact is that the charge / discharge cycle characteristics are greatly deteriorated due to expansion and contraction, and the characteristics of high capacity cannot be fully utilized.

  Further, there has been a problem that the electrode deteriorates during the charge / discharge cycle due to repeated expansion and contraction of the negative electrode active material, and eventually the electrode may break during use of the battery, leading to interruption of use or occurrence of a short circuit. In particular, when a positive electrode and a negative electrode are stacked and wound with an electrolyte in between, the step of the end of the active material layer, the lead, or the like is at one place due to the structural reason that the diameter of the winding center is small. When concentrated, the winding shape is significantly distorted, and the possibility of breakage due to electrode deterioration is high. This has been a serious problem especially in high-load charge / discharge cycles and overcharge charge / discharge cycles.

  Incidentally, conventionally, in a wound type battery using a carbon-based material as a negative electrode active material, the outermost periphery becomes a positive electrode, and the outermost peripheral side end of the negative electrode current collector is connected to the positive electrode current collector. The outer periphery of the winding body protrudes forward from the end portion, and the negative electrode lead is provided at the protruding portion, thereby eliminating the irregularities on the outermost periphery of the wound body, and the outermost periphery side end portion of the negative electrode lead and the positive electrode current collector. It has been proposed to prevent a short circuit (see, for example, Patent Document 7).

  The present invention has been made in view of such problems, and the object thereof is due to electrode deterioration when a negative electrode active material layer containing a single element, alloy or compound of a metal element or a metalloid element is used as the negative electrode active material. An object of the present invention is to provide a secondary battery capable of preventing breakage and improving charge / discharge cycle characteristics.

The secondary battery according to the present invention includes a positive electrode having an outer positive electrode active material layer on an outer peripheral surface of a strip-shaped positive electrode current collector and an inner positive electrode active material layer on an inner peripheral surface, and a negative electrode on the surface of the strip-shaped negative electrode current collector. A negative electrode having an active material layer is laminated with a separator interposed therebetween, and a wound body is provided. The negative electrode has tin and cobalt (as a negative electrode active material capable of occluding and releasing an electrode reactant ) Co) and carbon (C) as constituent elements, the carbon content is 9.9 mass% or more and 29.7 mass% or less, and the ratio of cobalt to the total of tin and cobalt is 30 mass%. The end of the outer positive electrode active material layer on the winding center side and the end of the inner positive electrode active material layer on the winding center side include a CoSnC-containing material that is 70% by mass or less and the winding center of the wound body. And the central angle formed with respect to the positive electrode current collector is 72 ° or more. A positive electrode lead is connected in the vicinity of the end on the center side, and the positive electrode lead has a central angle with respect to the winding center of the wound body from the end of the inner positive electrode active material layer on the winding center side within 30 ° in the winding direction. In addition, it is provided to avoid a region within 30 ° in the direction opposite to the winding direction. Here, the “winding direction” refers to a direction from the winding center side toward the winding outer peripheral side.

According to the secondary battery of the present invention, the negative electrode includes, as a constituent element, tin, cobalt (Co), and carbon (C) as a negative electrode active material capable of occluding and releasing an electrode reactant . A CoSnC-containing material having a carbon content of 9.9 mass% or more and 29.7 mass% or less and a ratio of cobalt to the total of tin and cobalt of 30 mass% or more and 70 mass% or less is included. Therefore, a high capacity can be obtained. Further, the central angle formed by the winding center side end of the outer positive electrode active material layer and the winding center side end of the inner positive electrode active material layer with respect to the winding center is 72 ° or more, and the positive electrode The lead is provided so as to avoid a region where the central angle with respect to the winding center from the end of the inner positive electrode active material layer on the winding center side is within 30 ° in the winding direction and within 30 ° in the direction opposite to the winding direction. Since it did in this way, distortion of the winding shape in the winding center side can be made small, and the fracture | rupture by deterioration of an electrode can be prevented. Therefore, cycle characteristics can be improved while maintaining a high capacity.

  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.

  FIG. 1 shows a cross-sectional structure of a secondary battery according to an 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 and a thermal resistance element (Positive Temperature Coefficient; PTC element) 16 provided inside the battery lid 14, have a gasket 17 in between. The battery can 11 is attached by being caulked, 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 interposed therebetween and wound in a spiral shape, and a center pin 24 is inserted in the center. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the wound body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows a cross-sectional configuration of the positive electrode 21 shown in FIG. 1 before winding. The positive electrode 21 is formed, for example, by providing an outer positive electrode active material layer 21B on the outer peripheral surface of a strip-shaped positive electrode current collector 21A and an inner positive electrode active material layer 21C on the inner peripheral surface. The outer positive electrode active material layer 21B is longer than the inner positive electrode active material layer 21C at the end on the winding center side, and one side of the positive electrode current collector 21A is formed by the single-sided region 21D, that is, the outer positive electrode active material layer 21B. Only the covered area.

  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 lead 25 described above is connected to the vicinity of the end portion on the winding center side of the positive electrode current collector 21A.

The outer cathode active material layer 21B and the inner cathode active material layer 21C include, for example, any one or more cathode materials capable of inserting and extracting lithium as an electrode reactant as a cathode active material, A conductive material such as a carbon material and a binder such as polyvinylidene fluoride may be included as necessary. 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, etc., or 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 a cross-sectional configuration of the negative electrode 22 shown in FIG. 1 before winding. The negative electrode 22 is obtained, for example, by providing a negative electrode active material layer 22B on both surfaces of a strip-shaped negative electrode current collector 22A. 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 can contain and release lithium as an electrode reactant as a negative electrode active material, and contains a negative electrode material containing at least one of a metal element and a metalloid element as a constituent element is doing. This is because a high energy density can be obtained by using such a negative electrode material. 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. Moreover, this negative electrode material may be used individually by 1 type, and 2 or more types may be mixed and used for it.

  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).

  The negative electrode active material layer 22B may further include other negative electrode active materials, and may include other materials that do not contribute to charging, such as a conductive agent, a binder, or a viscosity modifier. Examples of other negative electrode active materials include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon, and graphitizable carbon. Examples of the conductive agent include graphite fiber, metal fiber, and metal powder. Examples of the binder include a fluorine-based polymer compound such as polyvinylidene fluoride, or a synthetic rubber such as styrene butadiene rubber or ethylene propylene diene rubber. Examples of the viscosity modifier include carboxymethylcellulose.

  FIG. 4 illustrates an example of a cross-sectional configuration along line IV-IV of the wound body 20 illustrated in FIG. In FIG. 4, the separator 23 is omitted. The center angle θ () formed by the end 21B1 on the winding center side of the outer cathode active material layer 21B and the end 21C1 on the winding center side of the inner cathode active material layer 21C with respect to the winding center of the wound body 20 Hereinafter, the “center angle θ” is 72 ° or more, and the positive electrode lead 25 extends from the inner end portion vicinity region 21E, that is, from the end portion 21C1 on the winding center side of the inner positive electrode active material layer 21C. A region where the central angle of the wound body 20 with respect to the winding center is within 30 ° in the winding direction R and within 30 ° in the direction opposite to the winding direction R is provided. Thereby, in this secondary battery, the distortion of the winding shape on the winding center side can be reduced to prevent breakage due to electrode deterioration.

  The positional relationship between the end portion 21B1 on the winding center side of the outer cathode active material layer 21B and the end portion 21C1 on the winding center side of the inner cathode active material layer 21C may be such that the center angle θ is 72 ° or more, The length of the single-sided region 21D (see FIG. 2) is not particularly limited. For example, the single-sided region 21D may be provided over one or more rounds as shown in FIG. 4, or the single-sided region 21D may be less than one round as shown in FIG.

  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., and any one of these or a mixture of two or more May be.

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

  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 by using a doctor blade or a bar coater, and the solvent is dried. Then, the positive electrode mixture slurry is compression-molded by a roll press or the like, and then the outer positive electrode active material layer 21B. And the inner side positive electrode active material layer 21C is formed, and 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.

  After the wound body 20 is manufactured, the wound body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The body 20 is accommodated in the battery can 11, and the electrolyte is injected into the battery can 11 and impregnated in the separator 23. 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 the gasket 17 therebetween. Thereby, the secondary battery shown in FIG. 1 is completed.

  In this secondary battery, when charged, lithium ions are released from the positive electrode 21 and inserted in the negative electrode 22 through the electrolytic solution impregnated in the separator 23. When discharging is performed, lithium ions are released from the negative electrode 22 and inserted in the positive electrode 21 through the electrolytic solution impregnated in the separator 23. Here, since the center angle θ is 72 ° or more and the positive electrode lead 25 is provided so as to avoid the inner end vicinity region 21E, the end 21B1 of the outer positive electrode active material layer 21B, the positive electrode lead 25, etc. This step does not overlap the step at the end portion 21C1 of the inner cathode active material layer 21C, and the winding distortion on the winding center side is reduced. Thereby, the fracture | rupture by deterioration of an electrode is prevented and cycling characteristics are improved.

  As described above, according to the present embodiment, the negative electrode 22 can occlude and release the electrode reactant, and the negative electrode active material containing at least one of a metal element and a metalloid element as a constituent element. Since it was made to include, a high capacity can be obtained. Further, since the central angle θ is set to 72 ° or more and the positive electrode lead 25 is provided so as to avoid the inner end portion vicinity region 21E, the distortion of the winding shape on the winding center side can be reduced. . Therefore, cycle characteristics can be improved while maintaining a high capacity.

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

(Examples 1-3)
The secondary battery described in the above 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. The outer positive electrode active material layer 21B and the inner positive electrode active material layer 21C were formed by compression molding with a roll press machine to produce the positive electrode 21. At that time, the central angle θ was set to 72 ° in Example 1, 170 ° in Example 2, and 90 ° in Example 3.

  Subsequently, the positive electrode lead 25 made of aluminum was attached in the vicinity of the end portion on the winding center side of the positive electrode current collector 21A. At this time, the positive electrode lead 25 was provided avoiding the inner end vicinity region 21E.

  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 the diffraction angle 2θ = 20 ° and 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. After that, a nickel negative electrode lead 26 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 laminate. The wound body 20 was produced by winding. The maximum diameter of the body of the wound body 20 was 13 mm.

After the wound body 20 is manufactured, the wound body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The body 20 was accommodated in a battery can 11 having an inner diameter of 13.4 mm. After that, an electrolytic solution was injected into the battery can 11. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt at a content of 1 mol / dm ³ in a solvent obtained by mixing 50% by volume of ethylene carbonate and 50% by volume of diethyl carbonate was used.

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

  As Comparative Example 1 with respect to Examples 1 to 3, as shown in FIG. 6, a secondary battery was fabricated in the same manner as Examples 1 to 3 except that the central angle θ was 0 °. did. Further, as Comparative Example 2, as shown in FIG. 7, the end of the positive electrode lead 125 is aligned with the end portion 121C1 on the winding center side of the inner positive electrode active material layer 121C, and the positive electrode lead 125 is in the inner end vicinity region 121E. A secondary battery was fabricated in the same manner as in Example 1 except that the second battery was provided so as to overlap with the first electrode. 6 and 7, the same constituent elements as those shown in FIGS. 1 to 5 are denoted by the same reference numerals in the 100s.

  Five secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 thus obtained were produced, and the breaking strength of the positive electrode 21 was examined. The obtained results are shown in Table 1.

  In measurement of the breaking strength, first, after assembling the wound body 20, the positive electrode 21 is taken out, and the outer positive electrode active material layer 21B is covered with the end 21B1 on the winding center side of the outer positive electrode active material layer 21B as a substantially center. A test piece having a width of 15 mm and a length of 100 mm was taken so that the broken portion and the portion where the positive electrode current collector 21A was exposed were halved. The length direction of the test piece was made to coincide with the winding direction of the positive electrode 21. The breaking strength was 2.0 N / mm or more.

  Further, the cycle characteristics of each of the five secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were examined. The obtained results are shown in Table 2.

  As the cycle characteristics, the discharge capacity maintenance ratio at the 200th cycle (discharge capacity at the 200th cycle / discharge capacity at the second cycle) × 100 (%) with respect to the discharge capacity at the second cycle was determined, and 80% or more was determined as good . At that time, charge / discharge is performed under constant current / constant voltage charging under the condition of upper limit voltage 4.2V and current 1C in an environment of 45 ° C. and then constant current discharge under conditions of current 1C and final voltage 2.5V. Went. 1C is a current value at which the battery capacity can be discharged in one hour.

  As can be seen from Tables 1 and 2, in Examples 1 to 3 in which the central angle θ is 72 ° or more, the breaking strength and cycle characteristics are higher than those in Comparative Example 1 in which the central angle θ is 0 °. Good results were obtained for both.

  Further, when Example 1 and Comparative Example 2 were compared, Comparative Example 2 in which the positive electrode lead 125 overlapped the inner end portion vicinity region 121E was significantly lower than Example 1 in both break strength and cycle characteristics.

  That is, if the center angle θ is set to 72 ° or more and the positive electrode lead 25 is provided so as to avoid the inner end vicinity region 21E, the breaking strength of the positive electrode 21 can be increased and the cycle characteristics can be improved. I understood.

  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, 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. However, another electrolyte may be used instead of the electrolytic solution. Other electrolytes include, for example, a gel electrolyte in which an electrolyte is held in a polymer compound, a solid electrolyte having ionic conductivity, a mixture of a solid electrolyte and an electrolyte, or a solid electrolyte and a gel electrolyte. And a mixture thereof.

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

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

  Moreover, in the said embodiment and Example, although the cylindrical secondary battery which has a winding structure was demonstrated, all can be applied if this invention is a secondary battery which has a winding structure.

  Furthermore, in the above-described embodiment 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 magnesium Alternatively, the present invention can be applied to the case where a Group 2 element in a long-period periodic table such as calcium (Ca), another light metal such as aluminum, lithium, or an alloy thereof is used, and similar effects are obtained. 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 one 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 sectional drawing showing the structure along the IV-IV line of the wound body shown in FIG. It is sectional drawing showing the modification of the wound body shown in FIG. It is sectional drawing showing the structure of the wound body which concerns on the comparative example 1 of this invention. It is sectional drawing showing the structure of the wound body which concerns on the comparative example 2 of this invention.

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 ... Outer positive electrode active material layer, 21C ... Inner positive electrode active material layer, 21D ... Single-sided region, 21E ... Inner edge vicinity region, 22 ... Negative electrode, 22A ... Negative electrode current collector, 22B ... Negative electrode active material layer, 23 ... Separator 24 ... center pin, 25 ... positive electrode lead, 26 ... negative electrode lead.

Claims (1)

A positive electrode having an outer positive electrode active material layer on the outer peripheral surface of the strip-shaped positive electrode current collector and an inner positive electrode active material layer on the inner peripheral surface, and a negative electrode having a negative electrode active material layer on the surface of the strip-shaped negative electrode current collector Laminated with a separator in between, and provided with a wound wound body,
The negative electrode includes tin, cobalt (Co), and carbon (C) as constituent elements as a negative electrode active material capable of occluding and releasing an electrode reactant , and the carbon content is 9.9 masses. % or more and 29.7 mass% or less, and viewed including the CoSnC containing material ratio of cobalt to the total is not more than 30 wt% to 70 wt% of tin and cobalt,
The central angle formed by the end portion on the winding center side of the outer positive electrode active material layer and the end portion on the winding center side of the inner positive electrode active material layer with respect to the winding center of the wound body is 72 ° or more. And
In addition, a positive electrode lead is connected in the vicinity of an end portion on the winding center side of the positive electrode current collector, and the positive electrode lead is wound on the winding body from an end portion on the winding center side of the inner positive electrode active material layer. rechargeable batteries characterized in that the center angle is provided to avoid the area within 30 ° to 30 ° within and winding direction opposite the winding direction with respect to times center.

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