JP2007179765A - Negative electrode and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode having a high capacity and capable of improving a load characteristic; and to provide a battery using it. <P>SOLUTION: This negative electrode 10 includes a negative electrode collector 11, and a negative electrode active material layer 12 formed on the negative electrode collector 11. The negative electrode active material layer 12 contains natural graphite, and a surfactant such as polyoxyethylene nonyl phenyl ether. Thereby, a filling property of natural graphite in the negative electrode 10 can be improved, and permeability of an electrolyte in the negative electrode 10 can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a negative electrode containing natural graphite and a battery using the same.

  In recent years, many portable electronic devices such as a camera-integrated VTR (videotape recorder), a mobile phone, or a laptop computer have appeared, and their size and weight have been reduced. Accordingly, high energy density is required for batteries as portable power sources for these electronic devices. In addition, from the viewpoint of resource saving, development of a high-performance secondary battery that can be repeatedly charged is required. As such a secondary battery, for example, a lithium ion secondary battery has been proposed, and research and development are underway.

  In the lithium ion secondary battery, graphite is used for the negative electrode. However, in order to realize a higher capacity, it is increasing as a market need to design a higher volume density or area density.

Usually, the negative electrode of a lithium ion secondary battery is prepared by applying a paste containing artificial graphite and a binder to a current collector made of a metal foil, drying it, and rolling it as necessary. At that time, for example, if the volume density is increased to 1.7 g / cm ³ or more in order to increase the capacity, the permeability of the electrolytic solution is lowered and the load characteristics are lowered. In particular, when hydrophilic styrene butadiene rubber or carboxymethyl cellulose is used as a binder or thickener, the permeability of the electrolytic solution is further reduced.

On the other hand, natural graphite is known to have a high capacity, but is very soft because it is highly crystalline. Therefore, when designing the by increasing the volume density of the negative electrode for example ^{1.5g / cm 3 ~1.6g / cm 3} , will be filled with natural graphite becomes high, the pore portions of the internal electrodes is reduced, The permeability of the electrolytic solution will decrease.

Therefore, it has been proposed to spheroidize natural graphite (see, for example, Patent Document 1). According to this, the void | hole part inside an electrode can be ensured and the permeability of electrolyte solution can be improved.
JP-A-11-263612

  However, when the volume density is high, the permeability of the electrolytic solution is not sufficient, and further improvement is desired.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a negative electrode capable of improving load characteristics with a high capacity and a battery using the same.

  The negative electrode according to the present invention has a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, and the negative electrode active material layer contains natural graphite and a surfactant.

  The battery of the present invention is provided with an electrolyte together with a positive electrode and a negative electrode, and the negative electrode contains natural graphite and a surfactant.

  According to the negative electrode of the present invention, since the negative electrode active material layer includes natural graphite and a surfactant, it is possible to improve the fillability of the natural graphite and improve the permeability of the electrolytic solution. Can do. Therefore, according to the battery using this negative electrode, a high capacity and excellent load characteristics can be obtained.

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

  FIG. 1 is a cross-sectional view illustrating a configuration of a negative electrode 10 according to an embodiment of the present invention. The negative electrode 10 includes, for example, a negative electrode current collector 11 having a pair of opposed surfaces, and a negative electrode active material layer 12 provided on one surface of the negative electrode current collector 11. Although not shown, the negative electrode active material layers 12 may be provided on both surfaces of the negative electrode current collector 11.

  The negative electrode current collector 11 preferably has good electrochemical stability, electrical conductivity, and mechanical strength, and is made of a metal material such as copper (Cu), nickel (Ni), or stainless steel.

The negative electrode active material layer 12 includes natural graphite as a negative electrode active material. This is because the capacity can be increased. As natural graphite, the lattice spacing d ₀₀₂ in the C-axis direction measured by X-ray diffraction is preferably less than 0.336 nm. This is because the capacity can be further increased.

  Natural graphite is preferably spheroidized. This is because a hole portion in the negative electrode 12 can be secured. Spherical natural graphite need not be completely spherical, for example, natural graphite should be bent and swirled, including conical, cylindrical, or Including distorted shapes. For the spheroidization, for example, a natural graphite can be used in a Z-shaped vertical drop method in which a natural graphite is dropped along a path that is bent several times to the left and right to give an impact.

  When image analysis of natural graphite is performed, if the perimeter of natural graphite is 1 and the perimeter is L when replaced with a circle of the same area as the image of natural graphite, the circularity (L / l) is The number of particles of 0.85 or less is preferably 7% or more and 20% or less by number ratio. If there are many particles with a circularity (L / l) of 0.85 or less, the natural graphite with a high degree of spheroidization will decrease and the proportion of pores will decrease. Because it will do.

  Moreover, it is preferable that the average value of circularity (L / l) is 0.90 or more and 0.94 or less. When the average value of the circularity (L / l) is low, the ratio of the void portion is reduced, and conversely, when it is high, the edge portion of the natural graphite is crushed and it is difficult to occlude and release lithium (Li). Because it becomes.

The specific surface area of natural graphite is preferably ² m ² / g or more and 5.5 m ² / g or less. This is because if the specific surface area is small, the reaction area becomes small and the load characteristics deteriorate, and even if it is large, the reactivity with the electrolytic solution increases and the battery characteristics deteriorate. The specific surface area can be measured by, for example, the BET method.

  The negative electrode active material layer 12 also contains a surfactant. This is because the permeability of the electrolytic solution can be improved. Surfactants include nonionic, cationic, anionic, and zwitterionic types. For example, in the case of nonionic type, polyoxyethylene nonylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether , Fatty acid diethanolamide, alkyl trimethyl ammonium salt, dialkyl dimethyl ammonium chloride, alkyl pyridinium chloride, fatty acid salt, alpha sulfo fatty acid ester salt, alkyl benzene sulfonate, alkyl sulfate, alkyl sulfate triethanolamine, alkyl diphenyl ether disulfonate , Dialkyl succinate sulfonic acid sodium salt or monoalkyl succinate sulfonic acid disodium salt. Le carboxy betaine and the like. These surfactants may be added only to the negative electrode active material layer 12 or may be present so as to cover natural graphite.

  Examples of the method for coating the natural graphite with the surfactant include a method in which natural graphite and a solution containing the surfactant are kneaded with a planetary mixer and then dried. Also, spray coating method in which a solution containing a surfactant is sprayed on natural graphite convection in an air current, or an immersion method in which natural graphite is immersed in a dilute solution of surfactant, filtered and dried Also mentioned.

  The ratio of the surfactant to the natural graphite (surfactant / natural graphite) is preferably 10 mass ppm or more and 2 mass% or less. When the ratio of the surfactant is small, the effect of improving the permeability of the electrolytic solution is not sufficient, and when the ratio is large, the peel strength of the negative electrode active material layer 12 is lowered and the battery characteristics are lowered. is there.

  In addition to natural graphite, the negative electrode active material layer 12 may be used by mixing one or more of other negative electrode active materials capable of inserting and extracting lithium.

  The negative electrode active material layer 12 may further contain a binder. Examples of the binder include styrene butadiene rubber and polyvinylidene fluoride. In particular, when a hydrophilic binder is used, the surface of natural graphite becomes hydrophilic and the permeability of the electrolytic solution decreases, but the surface of natural graphite can be reduced by using the above-mentioned surfactant. Can be made hydrophobic, and the electrolyte can easily penetrate into the negative electrode.

  When the negative electrode 10 is suspended and its end is immersed in a solvent in which ethylene carbonate and dimethyl carbonate are mixed at an equal mass ratio, the permeation rate of the solvent is 2 mm / 10 min or more and 10 mm / 10 min or less. Is preferably 3 mm / 10 min or more and 7 mm / 10 min or less. This is because when the penetration rate is slow, the load characteristics are lowered, and when the penetration rate is fast, the electrode itself becomes brittle, the peel strength is lowered, and the battery characteristics are lowered.

  The negative electrode 10 can be manufactured as follows, for example.

  First, for example, a natural graphite coated with a surfactant, a binder, and, if necessary, a thickener are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a dispersion medium and pasted. A negative electrode mixture slurry. Subsequently, after applying this negative electrode mixture slurry to the negative electrode current collector 11 and drying the solvent, the negative electrode active material layer 12 is formed by compression molding with a roll press or the like. In addition, when natural graphite coated with a surfactant is not used, a surfactant may be added to the negative electrode mixture slurry.

  This negative electrode 10 is used for a secondary battery as follows, for example.

  FIG. 2 shows a cross-sectional structure of the secondary battery. This secondary battery is called a so-called cylindrical type, and a winding in which a strip-like positive electrode 31 and a strip-like negative electrode 10 are laminated and wound via a separator 32 inside a substantially hollow cylindrical battery can 21. An electrode body 30 is provided. The battery can 21 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 21, an electrolytic solution that is a liquid electrolyte is injected and impregnated in the separator 32. In addition, a pair of insulating plates 22 and 23 are respectively disposed perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 30.

  At the open end of the battery can 21, a battery lid 24, a safety valve mechanism 25 and a thermal resistance element (PTC element) 26 provided inside the battery lid 24 are interposed via a gasket 27. It is attached by caulking, and the inside of the battery can 21 is sealed. The battery lid 24 is made of the same material as the battery can 21, for example. The safety valve mechanism 25 is electrically connected to the battery lid 24 via the heat sensitive resistance element 26, and the disk plate 25A 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 24 and the wound electrode body 30 is cut off. When the temperature rises, the heat-sensitive resistor element 26 limits the current by increasing the resistance value, and prevents abnormal heat generation due to a large current. The gasket 27 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 33 is inserted in the center of the wound electrode body 30. A positive electrode lead 34 made of aluminum (Al) or the like is connected to the positive electrode 31 of the spirally wound electrode body 30, and a negative electrode lead 35 made of nickel or the like is connected to the negative electrode 10. The positive electrode lead 34 is welded to the safety valve mechanism 25 to be electrically connected to the battery lid 24, and the negative electrode lead 35 is welded to and electrically connected to the battery can 21.

  FIG. 3 shows an enlarged part of the spirally wound electrode body 30 shown in FIG. The negative electrode 10 has the above-described configuration. Thereby, the permeability of the electrolytic solution can be improved. In FIG. 3, the negative electrode active material layer 12 is represented as being formed on both surfaces of the negative electrode current collector 11.

  The positive electrode 31 has, for example, a structure in which a positive electrode active material layer 31B is provided on both surfaces or one surface of a positive electrode current collector 31A having a pair of opposed surfaces. The positive electrode current collector 31A is made of, for example, a metal foil such as an aluminum foil. The positive electrode active material layer 31B includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium, which is an electrode reactant, as a positive electrode active material. A conductive agent such as graphite or carbon black and a binder such as polyvinylidene fluoride may be included.

As a positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing compound such as lithium oxide, lithium phosphorus oxide, lithium sulfide, or an intercalation compound containing lithium is suitable, and two or more kinds are mixed. May be used. In particular, in order to increase the energy density, a lithium composite oxide or a lithium phosphorus oxide represented by the general formula Li _x MIO ₂ or Li _y MIIPO ₄ is preferable. In the formula, MI and MII preferably contain one or more transition metals. For example, cobalt (Co), nickel, manganese (Mn), iron, aluminum, vanadium (V), titanium (Ti) And at least one of zirconium (Zr) is preferably contained. The values of x and y vary depending on the charge / discharge state of the battery, and are usually values in the range of 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10. Specific examples of the lithium composite oxide represented by Li _x MIO ₂ include LiCoO ₂ , LiNiO ₂ , LiNi _0.5 Co _0.5 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , or LiMn ₂ O having a spinel crystal structure. ₄ and so on. Specific examples of the lithium phosphorus oxide represented by Li _y MIIPO ₄ include LiFePO ₄ and LiFe _0.5 Mn _0.5 PO ₄ .

  The separator 32 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be.

  The separator 32 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains, for example, a solvent and an electrolyte salt dissolved in this solvent.

  Examples of the solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene sulfite, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran. Non-water such as 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, acetate ester, butyrate ester, or propionate ester A solvent is mentioned. As the solvent, one kind may be used alone, or a plurality of kinds may be mixed and used. ,

  The solvent preferably contains 4-fluoro-1,3-dioxolan-2-one. The edge portion of the natural graphite described above has high reactivity and decomposes the electrolytic solution. However, by including 4-fluoro-1,3-dioxolan-2-one, a stable film can be formed on the negative electrode 10. This is because battery characteristics such as charge / discharge efficiency can be improved.

  The content of 4-fluoro-1,3-dioxolan-2-one in the electrolytic solution is preferably in the range of 0.1% by mass to 30% by mass. This is because if the content is small, the effect of improving the charge / discharge efficiency is not sufficient, and if the content is large, the internal resistance increases.

Examples of the electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiCl, or LiBr. Any one of the electrolyte salts may be used alone, or a plurality of them may be mixed and used.

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

  First, for example, the negative electrode 10 is produced as described above. Also, for example, a positive electrode active material, and optionally a conductive agent and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is dispersed in a dispersion medium to produce a positive electrode mixture slurry. Next, this positive electrode mixture slurry is applied to the positive electrode current collector 31A, dried, and compression molded to form the positive electrode active material layer 31B, thereby producing the positive electrode 31.

  Subsequently, the positive electrode lead 34 is attached to the positive electrode current collector 31A by welding or the like, and the negative electrode lead 35 is attached to the negative electrode current collector 11 by welding or the like. After that, the positive electrode 31 and the negative electrode 10 are laminated and wound via the separator 32, and the tip of the positive electrode lead 34 is welded to the safety valve mechanism 25 and the tip of the negative electrode lead 35 is welded to the battery can 21. The wound positive electrode 31 and negative electrode 10 are sandwiched between a pair of insulating plates 22 and 23 and housed inside the battery can 21. Next, for example, an electrolytic solution is injected into the battery can 21 and impregnated in the separator 32. After that, the battery lid 24, the safety valve mechanism 25, and the heat sensitive resistance element 26 are fixed to the opening end of the battery can 21 by caulking through a gasket 27. Thereby, the secondary battery shown in FIGS. 2 and 3 is formed.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 31 </ b> B and inserted in the negative electrode active material layer 12 through the electrolytic solution impregnated in the separator 32. Next, when discharging is performed, lithium ions are released from the negative electrode active material layer 12 and inserted in the positive electrode active material layer 31B through the electrolytic solution impregnated in the separator 32. In this secondary battery, since natural graphite and a surfactant are contained, for example, even when the volume density is increased, the permeability of the electrolytic solution is improved while maintaining a high capacity.

  Thus, according to the secondary battery according to the present embodiment, since the negative electrode active material layer 12 includes natural graphite and a surfactant, it is possible to improve the fillability of natural graphite, The permeability of the electrolytic solution can be improved. Therefore, a high capacity and excellent load characteristics can be obtained.

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

(Examples 1-1 to 1-5)
First, flaky natural graphite was spheroidized by a Z-shaped vertical drop method. At that time, the dropping speed and the like were appropriately adjusted. Subsequently, the degree of spheroidization of the spheroidized natural graphite (hereinafter referred to as spheroidized natural graphite) was measured using a flow particle image analyzer (FPIA3000 manufactured by SYSMEX). Specifically, 50 ml of purified water and poly (oxyethylene) = octylphenyl ether as a dispersion medium are added to spheroidized natural graphite, and 300 W, subjected to ultrasonic waves for 3 seconds, is measured by instrument suction. Went. As a result, the number of particles having a circularity (L / l) of 0.85 or less was 8.7%, and the average value of the circularity (L / l) was 0.936.

  Subsequently, the produced spheroidized natural graphite and a solution in which polyoxyethylene nonylphenyl ether was dissolved as a surfactant were kneaded by a planetary mixer, and then dried at 120 ° C. for 10 hours or more to obtain spheroidized natural graphite. The surface of was coated with polyoxyethylene nonylphenyl ether. At that time, the solid content concentration during kneading was set to 53 mass%. The ratio of polyoxyethylene nonylphenyl ether to spheroidized natural graphite was 2 mass%, 1 mass%, 4500 massppm, 200 massppm or 10 massppm.

Using the produced polyoxyethylene nonylphenyl ether and spherical natural graphite (hereinafter referred to as coated spherical natural graphite), a negative electrode 10 was produced. First, 96.5% by mass of spherical natural graphite coated, 2% by mass of styrene butadiene rubber as a binder, and 1.5% by mass of carboxymethyl cellulose as a thickener were prepared to prepare a negative electrode mixture, After being dispersed in water as a dispersion medium to obtain a paste-like negative electrode mixture slurry, this negative electrode mixture slurry is applied to one side of a negative electrode current collector 11 made of a copper foil having a thickness of 15 μm, dried, compression molded, and subjected to negative electrode active. The material layer 12 was formed and the negative electrode 12 was produced. At that time, the area density of the surface provided with the negative electrode active material layer 12 is 16.0 g / cm ^{2 to} 17.0 g / cm ^2, and the volume density is 1.6 g / cm ^{3 to} 1.7 g / cm ² . was adjusted so that the cm ^3.

  The prepared negative electrode 10 was cut into a length of 25 mm and a width of 10 mm to prepare a test piece, and the end portion in the length direction of the test piece was immersed in a solvent in which propylene carbonate and dimethyl carbonate were mixed at an equal mass ratio. The height at which the solvent permeated and increased after 10 minutes was determined. The results are shown in Table 1.

  Moreover, the negative electrode 10 produced similarly was cut | disconnected to length 150mm and width 32mm, the test piece was produced, and after peeling the negative electrode collector 11 from this test piece about half, the peeling strength was measured. At that time, the portion where the negative electrode active material layer 12 was not peeled was fixed, and the negative electrode current collector 11 of the peeled portion was pulled to peel the negative electrode current collector 11. The peel strength was measured using Shimadzu Autograph AG-LSMS type series manufactured by Shimadzu Corporation. The results are shown in Table 1.

Subsequently, a coin-type secondary battery as shown in FIG. 4 was produced using the negative electrode 10 produced in the same manner. In this secondary battery, a negative electrode 10 and a test electrode 41 made of lithium metal are stacked via a separator 42 impregnated with an electrolyte, sandwiched between an outer can 43 and an outer cup 44, and via a gasket 45. It is a squeezed one. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ as an electrolyte salt to 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate were mixed in an equal volume was used. The negative electrode 10 and the test electrode 41 were punched into a disk shape having a diameter of 15.5 mm. Further, the coin-type test battery had a diameter of 20 mm and a thickness of 2.5 mm.

  About the produced test battery, the load characteristic was investigated as follows. First, constant current charging is performed until the battery voltage reaches 0 V at a constant current of 0.85 mA, then constant voltage charging is performed until the current reaches 0.005 mA at a constant voltage of 0 V, and then a constant current of 0.85 mA. Discharge was performed until the battery voltage reached 1.5 V with current. Subsequently, constant current charging was performed until the battery voltage reached 0 V at a constant current of 0.85 mA, then constant voltage charging was performed until the current reached 0.005 mA at a constant voltage of 0 V, and then a constant current of 20 mA. The battery was discharged until the battery voltage reached 1.5 V, and the discharge capacity at 20 mA was determined. For the load characteristics, the discharge capacity at 20 mA per 1 g of spheroidized natural graphite was determined. The results are shown in Table 1. In the test battery, the process in which lithium is occluded in natural graphite is called charging.

  As can be seen from Table 1, as the ratio of polyoxyethylene nonylphenyl ether to the spheroidized natural graphite increases, the permeation rate of the solvent increases and the load characteristics are improved. There was a tendency for the peel strength to decrease.

  That is, if the negative electrode 10 contains natural graphite and a surfactant, the load characteristics can be improved, and the ratio of the surfactant to the natural graphite is 10 mass ppm or more and 2 mass% or less. It was found that it was preferable.

(Examples 2-1 to 2-3)
The production conditions of the spheroidized natural graphite were adjusted, and the number ratio of particles having a circularity (L / l) of 0.85 or less and the average value of the circularity (L / l) were changed as shown in Table 2. Otherwise, spherical natural graphite and coin-type test batteries coated were prepared in the same manner as in Example 1-4. At that time, when the specific surface area of the produced spherical natural graphite was measured by the BET method, it was as shown in Table 2. In the BET method, the adsorbate was nitrogen and degassing was performed at 120 ° C. for 30 minutes.

  About the produced test battery, it carried out similarly to Examples 1-1 to 1-6, and calculated | required load characteristics. The results are shown in Table 2.

  As can be seen from Table 2, the load characteristics are the number ratio of particles having a circularity (L / l) of 0.85 or less and the average value of the circularity (L / l) as the specific surface area decreases. As it became larger, it increased, and after showing a maximum value, a tendency to decrease was observed.

That is, if the number ratio of particles having a circularity (L / l) of 0.85 or less is 7% or more and 20% or less, or the average value of the circularity (L / l) is 0.90. It has been found that it is preferable if the specific surface area of the spheroidized natural graphite is 2 m ² / g or more and 5.5 m ² / g or less if it is 0.94 or less.

(Examples 3-1 to 3-6)
The cylindrical secondary battery shown in FIG. 2 was produced as follows.

First, 0.5 mol of lithium carbonate (Li ₂ CO ₃ ) and 1 mol of cobalt carbonate (CoCO ₃ ) are mixed, and this mixture is fired in air at 900 ° C. for 5 hours to obtain a lithium cobalt composite oxide (LiCoO ₂ ) powder. Was synthesized. When the obtained lithium cobalt composite oxide was subjected to X-ray diffraction measurement, it was in good agreement with the LiCoO ₂ peak registered in the JCPDS file. Next, this lithium cobalt composite oxide was pulverized to obtain a powder having a cumulative 50% particle size of 15 μm obtained by a laser diffraction method, and this was used as a positive electrode active material. 95% by mass of the obtained positive electrode active material powder and 5% by mass of lithium carbonate powder were mixed, 94% by mass of this mixture, 3% by mass of ketjen black as a conductive agent, and polyvinylidene fluoride 3 as a binder. The positive electrode mixture slurry was prepared by mixing with N-methyl-2-pyrrolidone as a dispersion medium. Next, this positive electrode mixture slurry was uniformly applied to both surfaces of a positive electrode current collector 31A made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and compression-molded to form a positive electrode active material layer 31B, thereby producing a positive electrode 31. . After that, the positive electrode lead 34 made of aluminum was attached to one end of the positive electrode current collector 31A.

Further, the negative electrode 10 was produced in the same manner as in Example 1-4. At that time, the negative electrode active material layer 12 was formed on both surfaces of the negative electrode current collector 11. The specific surface area of the coated spheroidized natural graphite was 3.80 m ² / g. Thereafter, a negative electrode lead 35 made of nickel was attached to one end of the negative electrode current collector 12.

  After each of the positive electrode 31 and the negative electrode 10 is prepared, a separator 32 made of a microporous polyethylene stretched film having a thickness of 25 μm is prepared, and the negative electrode 10, the separator 32, the positive electrode 31, and the separator 32 are sequentially laminated. A jelly roll type wound electrode body 30 having an outer diameter of 14 mm was produced.

After producing the wound electrode body 30, the wound electrode body 30 is sandwiched between the pair of insulating plates 22 and 23, the negative electrode lead 35 is welded to the battery can 21, and the positive electrode lead 34 is welded to the safety valve mechanism 25. The wound electrode body 30 was housed inside a nickel-plated iron battery can 21. After that, the electrolytic solution was injected into the battery can 21 by a reduced pressure method. In the electrolyte, a solvent in which ethylene carbonate and diethyl carbonate are mixed in an equal volume is mixed with propylene carbonate and ethylene furphyto, and if necessary, 4-fluoro-1,3-dioxolan-2-one, Furthermore, it was used with LiPF ₆ dissolved at a 1.45 mol / kg as an electrolyte salt. The contents of propylene carbonate and ethylene sulfite in the electrolytic solution were 4% by mass and 1% by mass, respectively. Further, the content of 4-fluoro-1,3-dioxolan-2-one in the electrolytic solution is 30% by mass in Example 3-1, 20% by mass in Example 3-2, and Example 3-3. In Example 3-4, the content was 5% by mass, in Example 3-4, 1% by mass, in Example 3-5, 0.1% by mass, and in Example 3-6, 0% by mass.

  After injecting the electrolytic solution, the battery can 21 is caulked through the gasket 27 to fix the safety valve mechanism 25, the heat sensitive resistance element 26, and the battery cover 24, and the cylindrical secondary battery shown in FIG. Produced.

  About the produced secondary battery, charging / discharging was performed, and initial stage charging / discharging efficiency and cycling characteristics were investigated. At that time, charging was performed at a constant current of 1 C until the battery voltage reached 4.2 V, and then at a constant voltage of 4.2 V until the total charging time reached 4 hours. Discharge was performed at a constant current of 0.5 C until the battery voltage reached 3.0V. This charge / discharge is repeated, and the initial charge / discharge efficiency is the ratio of the discharge capacity of the first cycle to the charge capacity of the first cycle, that is, (discharge capacity of the first cycle / charge capacity of the first cycle) × 100 (%) I asked for it. The cycle characteristics were obtained from the ratio of the discharge capacity at the 300th cycle to the discharge capacity at the first cycle, that is, (discharge capacity at the 300th cycle / discharge capacity at the first cycle) × 100 (%). The results are shown in Table 3. 1C and 0.5C are current values at which the theoretical capacity can be discharged in 1 hour and 2 hours, respectively.

  As shown in Table 3, according to Examples 3-1 to 3-5 using 4-fluoro-1,3-dioxolan-2-one, rather than Example 3-6 not using this, The initial charge / discharge efficiency and cycle characteristics were improved.

  That is, it was found that the battery characteristics can be further improved if 4-fluoro-1,3-dioxolan-2-one is included in the electrolytic solution.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, a cylindrical secondary battery has been specifically described. However, the present invention is not limited to a coin type, a square type, a button type, a thin type, as shown in FIG. The present invention can be similarly applied to a secondary battery having another shape using an exterior member such as a large-size or laminated film, or a secondary battery having another structure such as a laminated structure. Further, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

  Further, in the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium (Na) or potassium (K), or magnesium (Mg) or calcium (Ca). The present invention can also be applied to the case of using alkaline earth metals such as other light metals or other light metals such as aluminum. At that time, a positive electrode active material or a solvent that can occlude and release the electrode reactant is selected according to the electrode reactant.

  Furthermore, in the above-described embodiments and examples, the case where an electrolytic solution is used as the electrolyte has been described. However, a so-called gel electrolyte in which the electrolytic solution is held in a holding body such as a polymer compound, or has ionic conductivity. A solid electrolyte or a mixture thereof may be used. Examples of the polymer compound used for the gel electrolyte include fluorine-based polymer compounds such as polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene, and ether-based compounds such as polyethylene oxide or a crosslinked product containing polyethylene oxide. Examples thereof include a polymer compound, polyacrylonitrile, polymethacrylate or polyacrylate containing repeating units. In particular, a fluorine-based polymer compound is desirable from the viewpoint of redox stability. Any one of these polymer compounds may be used alone, or two or more thereof may be mixed and used.

  As the solid electrolyte, for example, a polymer 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. In this case, 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 or polyacrylate, or a mixture thereof, or in the molecule It can be used after being copolymerized. As the inorganic solid electrolyte, lithium nitride, lithium iodide, or the like can be used.

It is sectional drawing showing the structure of the negative electrode which concerns on one embodiment of this invention. It is sectional drawing showing the structure of the secondary battery using the negative electrode shown in FIG. It is sectional drawing which expands and represents a part of winding electrode body shown in FIG. It is sectional drawing of the test battery produced in the Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Negative electrode, 11 ... Negative electrode collector, 12 ... Negative electrode active material layer, 21 ... Battery can, 22, 23 ... Insulation board, 24 ... Battery cover, 25 ... Safety valve mechanism, 25A ... Disc board, 26 ... Heat resistance Element 27, 45 ... Gasket, 30 ... Winding electrode body, 31 ... Positive electrode, 31A ... Positive electrode current collector, 31B ... Positive electrode active material layer, 32, 42 ... Separator, 33 ... Center pin, 34 ... Positive electrode lead, 35 ... negative electrode lead, 41 ... test electrode, 43 ... outer can, 44 ... outer cup

Claims (19)

A negative electrode current collector, and a negative electrode active material layer provided on the negative electrode current collector,
The negative electrode active material layer includes natural graphite and a surfactant.   The surfactant is polyoxyethylene nonyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, fatty acid diethanolamide, alkyl trimethyl ammonium salt, dialkyl dimethyl ammonium chloride, alkyl pyridinium chloride, fatty acid salt, alpha Group consisting of sulfo fatty acid ester salt, alkylbenzene sulfonate, alkyl sulfate, alkyl sulfate triethanolamine, alkyl diphenyl ether disulfonate, sodium dialkyl succinate sulfonate, disodium monoalkyl succinate sulfonate and alkyl carboxybetaine The negative electrode according to claim 1, comprising at least one of the above.   The negative electrode according to claim 1, wherein the natural graphite is coated with the surfactant.   The negative electrode according to claim 1, wherein the natural graphite is spheroidized.   2. The negative electrode according to claim 1, wherein a ratio of the surfactant to the natural graphite (surfactant / natural graphite) is 10 mass ppm or more and 2 mass% or less.   2. The negative electrode according to claim 1, wherein a permeation rate of a solvent in which ethylene carbonate and dimethyl carbonate are mixed at an equal mass ratio is 2 mm / 10 min or more and 10 mm / 10 min or less.   When an image analysis of the natural graphite is performed, if the perimeter of the natural graphite is l and the perimeter is L when replaced with a circle having the same area as the natural graphite image, the circularity (L / 2. The negative electrode according to claim 1, wherein the number of the particles having l) of 0.85 or less is 7% or more and 20% or less.   When image analysis of the natural graphite is performed, if the perimeter of the natural graphite is l and the perimeter of the circle is L when replaced with a circle having the same area as the natural graphite image, the circularity ( 2. The negative electrode according to claim 1, wherein an average value of L / l) is 0.90 or more and 0.94 or less. ^2. The negative electrode according to claim 1, wherein the natural graphite has a specific surface area of 2 m ² / g or more and 5.5 m ² / g or less. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode includes natural graphite and a surfactant.   The surfactant is polyoxyethylene nonyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, fatty acid diethanolamide, alkyl trimethyl ammonium salt, dialkyl dimethyl ammonium chloride, alkyl pyridinium chloride, fatty acid salt, alpha Group consisting of sulfo fatty acid ester salt, alkylbenzene sulfonate, alkyl sulfate, alkyl sulfate triethanolamine, alkyl diphenyl ether disulfonate, sodium dialkyl succinate sulfonate, disodium monoalkyl succinate sulfonate and alkyl carboxybetaine The battery according to claim 10, comprising at least one of the above.   The battery according to claim 10, wherein the natural graphite is coated with the surfactant.   The battery according to claim 10, wherein the electrolyte includes 4-fluoro-1,3-dioxolan-2-one.   The battery according to claim 10, wherein the natural graphite is spheroidized.   11. The battery according to claim 10, wherein a ratio of the surfactant to the natural graphite (surfactant / natural graphite) is 10 mass ppm or more and 2 mass% or less.   11. The battery according to claim 10, wherein the negative electrode has a permeation rate of a solvent obtained by mixing ethylene carbonate and dimethyl carbonate at an equal mass ratio of 2 mm / 10 min or more and 10 mm / 10 min or less.   When an image analysis of the natural graphite is performed, if the perimeter of the natural graphite is l and the perimeter is L when replaced with a circle having the same area as the natural graphite image, the circularity (L / 11. The battery according to claim 10, wherein the particles having l) of 0.85 or less are in a number ratio of 7% or more and 20% or less.   When image analysis of the natural graphite is performed, if the perimeter of the natural graphite is l and the perimeter of the circle is L when replaced with a circle having the same area as the natural graphite image, the circularity ( The battery according to claim 10, wherein an average value of L / l) is 0.90 or more and 0.94 or less. 11. The battery according to claim 10, wherein the natural graphite has a specific surface area of 2 m ² / g or more and 5.5 m ² / g or less.

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