JP4501638B2 - Lithium ion 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 lithium ion 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 (see, for example, 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 2004-87324 A

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 deterioration of charge / discharge cycle characteristics due to expansion and contraction is large, and the actual situation is that the characteristics of high capacity have not been fully utilized.

  Moreover, when using these negative electrode active materials, a negative electrode expand | swells and shrinks greatly with charging / discharging. Therefore, in particular, when used as a wound body in which a positive electrode and a negative electrode are laminated and wound with an electrolyte in between, if the roundness of the wound body is low and the strain is large, the pressure applied to the electrode is not uniform depending on the location. . While the separator may be compressed in the high pressure area and a micro short circuit may occur, the gap between the electrodes becomes large in the low pressure area, causing lithium deposition, and deterioration of load characteristics and charge / discharge cycle characteristics. Will become remarkable. Furthermore, when inserting and using a wound body in a comparatively soft battery can, there exists a possibility that a battery can may be pushed and deform | transformed from an inner side by expansion | swelling of a negative electrode.

  Incidentally, conventionally, it has been proposed to increase the roundness of the wound body by setting the central angle formed by the positive electrode lead and the negative electrode lead to the winding center to be approximately 120 ° or 240 °. (For example, refer to Patent Document 7) However, it is desired to further increase the roundness.

The present invention has been made in view of such problems, and its purpose is to increase the roundness of the wound body by using an alloy material as a negative electrode active material, and to improve the roundness of the wound body between the positive electrode and the negative electrode. An object of the present invention is to provide a lithium ion secondary battery that can make the pressure between them uniform and improve the charge / discharge cycle characteristics.

A lithium ion secondary battery according to the present invention comprises a separator having a positive electrode having a positive electrode active material layer on a surface of a strip-shaped positive electrode current collector and a negative electrode having a negative electrode active material layer on a surface of the strip-shaped negative electrode current collector. The negative electrode includes a negative electrode active material capable of inserting and extracting lithium (Li) as an electrode reactant , and the negative electrode active material includes constituent elements. tin, cobalt (Co), and the carbon (C), not more than 29.7 mass% content of more than 9.9 mass% of carbon, and the ratio of cobalt to the total of tin and cobalt 30 It is a CoSnC-containing material that is not less than 70% by mass . This CoSnC-containing material has a low crystalline or amorphous phase containing tin, cobalt, and carbon, and at least a part of carbon as a constituent element is bonded to tin or cobalt, The half width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more. In the positive electrode active material layer, the central angle formed by the end on the winding outer periphery side and the end on the winding center side with respect to the winding center of the winding body extends from the end on the winding center side in the winding direction. It is within the range of 0 ° or more and −90 ° or less. Here, the “winding direction” is a direction from the winding center side to the winding outer peripheral side, and “−” represents a direction opposite to the winding direction.

According to the lithium ion secondary battery of the present invention, the negative electrode includes a negative electrode active material capable of inserting and extracting an electrode reactant, and the negative electrode active material includes tin, cobalt (Co) as constituent elements , and the carbon (C), is 29.7 wt% or less than 9.9 wt%, and the ratio of cobalt to the total of tin and cobalt is at least 30 mass% 70 mass% carbon content The CoSnC-containing material has a low crystalline or amorphous phase containing tin, cobalt, and carbon, and at least a part of carbon as a constituent element is tin or cobalt. In addition to being coupled, the half-value width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more, so that a high capacity can be obtained. Further, the central angle formed by the end portion on the winding outer periphery side and the end portion on the winding center side of the positive electrode active material layer with respect to the winding center is 0 ° or more in the winding direction from the end portion on the winding center side. Since it is within the range of −90 ° or less, the roundness of the wound body can be increased, and the pressure between the positive electrode and the negative electrode inside the wound body can be made uniform. Therefore, the occurrence of a short-circuit due to the compression of the separator can be eliminated, and the deterioration of load characteristics and charge / discharge cycle characteristics due to lithium deposition can be prevented. Therefore, cycle characteristics can be improved while maintaining a high capacity. Further, by increasing the roundness and making the pressure inside the wound body uniform, the chemical reaction can be caused uniformly and the reliability can be improved.

  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 obtained, for example, by providing a positive electrode active material layer 21B on both surfaces of a strip-shaped positive electrode current collector 21A. 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, 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 metalloid element as another constituent element , that is, cobalt or tin . 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 carbon 1s orbital (C1s) appears at 284.5 eV in an energy calibrated apparatus so that the peak of 4f orbit of gold atom (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. It is bound with a metal element , ie cobalt or tin .

  In XPS measurement, for example, the C1s peak is used for correcting 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, and this 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 positive electrode active material layer 21B has a center angle θ (hereinafter simply referred to as “center angle θ”) formed by the end portion 21C on the winding outer periphery side and the end portion 21D on the winding center side with respect to the winding center of the wound body. .) In the winding direction R from the end portion 21D on the winding center side within a range of 0 ° to −90 °. Thereby, in this secondary battery, the roundness of the wound body 20 is increased, the pressure between the positive electrode 21 and the negative electrode 22 inside the wound body 20 is made uniform, and cycle characteristics and reliability are improved. Can be done.

  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.

  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 laminated with the separator 23 therebetween, and are wound many times in the winding direction shown in FIGS.

  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 central angle θ is in the range of 0 ° or more and −90 ° or less in the winding direction R from the end portion 21D on the winding center side, the roundness of the wound body 20 is high, and the winding is performed. The pressure between the positive electrode 21 and the negative electrode 22 inside the body 20 is uniform. Therefore, the occurrence of a short-circuit due to the compression of the separator 23 is eliminated, and deterioration of load characteristics and charge / discharge cycle characteristics due to lithium deposition is also prevented. This improves the cycle characteristics.

  As described above, in the present embodiment, 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. Therefore, a high capacity can be obtained. Further, since the central angle θ is set in the range of 0 ° or more and −90 ° or less in the winding direction R from the end portion 21D on the winding center side, the roundness of the wound body 20 is increased and the winding is performed. The pressure between the positive electrode 21 and the negative electrode 22 inside the body 20 can be made uniform. Therefore, cycle characteristics and reliability can be improved while maintaining a high capacity.

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

(Examples 1-4)
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. By firing for a time, a 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, the 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 25 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, and the negative electrode 22 was produced. 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 laminated body. The wound body 20 was produced by winding. The maximum diameter of the body of the wound body 20 was 13 mm. At this time, in the first embodiment, the central angle θ is 0 ° in the winding direction R from the end portion 21D on the winding center side, that is, the end portion 21C on the winding outer periphery side and the end portion 21D on the winding center side turn around. It overlapped in the direction. In Example 2, the central angle θ was −30 °, Example 3 was −60 °, and Example 4 was −90 °. In addition, “−” represents a direction opposite to the winding direction R.

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 Examples 1 to 4 with respect to Examples 1 to 4, except that the central angle was 60 ° in Comparative Example 1, 120 ° in Comparative Example 2, 180 ° in Comparative Example 3, and 240 ° in Comparative Example 4. Produced secondary batteries in the same manner as in Examples 1 to 4.

  Five secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 4 thus obtained were produced, and the cycle characteristics were examined. The obtained results are shown in Table 1.

  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 to be 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 Table 1, according to Examples 1 to 4 in which the center angle θ is in the range of 0 ° or more and −90 ° or less in the winding direction R from the end portion 21D on the winding center side, the center angle is 60 The capacity retention rate was improved as compared with Comparative Examples 1 to 4 in the range of ° to 240 °.

  That is, it has been found that the cycle characteristics can be improved by setting the central angle θ within the range of 0 ° or more and −90 ° or less in the winding direction R from the end portion 21D on the winding center side.

  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.

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: End portion on winding outer periphery side, 21D: End portion on winding center side, 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 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. Equipped with round bodies,
The negative electrode includes a negative electrode active material capable of occluding and releasing lithium (Li) as an electrode reactant , and the negative electrode active material includes tin, cobalt (Co), and carbon (C) as constituent elements. and in the content of carbon is 29.7 wt% 9.9 wt%, and in CoSnC containing material ratio of cobalt is less than 30 mass% to 70 mass% to the total of tin and cobalt Yes,
The CoSnC-containing material has a low crystalline or amorphous phase containing tin, cobalt, and carbon, and at least part of carbon as a constituent element is bonded to tin or cobalt, The half width of the diffraction peak obtained by X-ray diffraction is 1.0 ° or more,
The positive electrode active material layer has a central angle formed by an end on the winding outer periphery side and an end on the winding center side with respect to the winding center of the winding body from the end on the winding center side. Within the range of 0 ° to -90 ° in the rotation direction
Lithium ion secondary battery.

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