JP2005340025A - Negative electrode material and battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery excellent in cycle characteristics even when discharging at a high capacity and a high load rate, and a negative electrode material used therefor.
A belt-like positive electrode 21 and a negative electrode 22 are wound with a separator 23 interposed therebetween. The negative electrode 21 is made of a carbon material having a first peak with a large particle diameter and a second peak with a small particle diameter in the cumulative volume particle size distribution curve, and the accumulated amount of passage of the second peak is 1% or more and 15% or less, and A negative electrode material in which the ratio of the particle size of the second peak to the particle size of the first peak is greater than 0 and 0.05 or less is included.
[Selection] Figure 1

Description

  The present invention relates to a negative electrode material containing carbon materials having different particle diameters, and a battery using the same.

  2. Description of the Related Art In recent years, electronic devices have been improved in performance, size, and portability due to advances in electronic technology, and a secondary battery having a high energy density is strongly demanded as a power supply source used in these electronic devices. Conventionally, secondary batteries such as nickel-cadmium batteries and lead batteries have been used for these electronic devices. However, these secondary batteries have a low discharge potential and a high energy density as required. Not enough from a battery perspective.

  As a secondary battery having a high energy density, a material capable of occluding and releasing lithium ions, such as lithium, a lithium alloy, or a carbon material, is used as a negative electrode active material. Research and development of non-aqueous electrolyte secondary batteries using lithium composite oxides such as materials have been actively carried out, and in particular, lithium ion secondary batteries using carbon materials as negative electrode materials have been put into practical use and are commercially available. .

Although this battery has a high battery voltage and excellent cycle characteristics, in order to further increase the capacity or improve the cycle characteristics, for example, a plurality of carbon materials having different particle diameters may be used as the negative electrode active material. (For example, refer to Patent Document 1)
JP-A-10-199526

  By the way, among the battery performance required as a secondary battery that can replace the conventional nickel-cadmium battery or lead battery, there is a cycle life characteristic at a high load. In particular, a secondary battery used as a power supply source for portable devices such as a camera-integrated VTR, a cellular phone, and a laptop personal computer is positioned as one of the important performances with a cycle life of about 2C discharge.

  In a conventional lithium ion secondary battery, for example, a long life of about 1200 cycles has been confirmed for discharge at a low load rate. However, when charging and discharging are repeated, the conductivity decreases due to the expansion and contraction of the negative electrode active material, and this decrease in conductivity strongly influences the decrease in capacity, particularly in a cycle due to discharge at a high load rate. For example, if charging / discharging is repeated with 2C discharge, only a life of about 1/10 or less can be obtained compared with repeating charging / discharging at a low load rate.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery having a high capacity and a high load rate, and having excellent cycle characteristics, and a negative electrode material used therefor. .

  The negative electrode material according to the present invention is made of a carbon material having a first peak with a large particle diameter and a second peak with a small particle diameter in a cumulative volume particle size distribution curve, and the accumulated amount of passage of the second peak is 1% or more and 15% or less. The ratio of the second peak particle diameter to the first peak particle diameter (second peak particle diameter / first peak particle diameter) is greater than 0 and less than or equal to 0.05.

  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the negative electrode is made of a carbon material having a first peak having a large particle diameter and a second peak having a small particle diameter in a cumulative volume particle size distribution curve. The ratio of the second peak particle diameter to the first peak particle diameter (second peak particle diameter / first peak particle diameter) is 1% or more and 15% or less. A negative electrode material that is greater than 0 and less than or equal to 0.05 is included.

  According to the negative electrode material of the present invention, the accumulated amount of the second peak having a small particle diameter in the cumulative volume particle size distribution curve is set to 1% or more and 15% or less, and the second peak with respect to the particle diameter of the first peak having a large particle diameter is reduced. Since the ratio of particle diameters is set to be larger than 0 and 0.05 or less, for example, in the battery of the present invention, the energy density can be increased, conductivity can be ensured, and deterioration in cycle characteristics can be suppressed. it can.

  In particular, when the negative electrode material contains fibrous carbon having an average length of 2 μm to 10 μm and an average width of 0.05 μm to 0.5 μm, a high effect can be obtained.

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

  The negative electrode material according to an embodiment of the present invention functions as a negative electrode active material, and includes, for example, two or more types of carbon materials having different sizes, and measuring a cumulative volume particle size distribution, Two distribution peaks are obtained. The energy density can be increased only with a large particle size, but the contact between carbon materials decreases due to expansion / contraction caused by charging / discharging, and the conductivity decreases, while the particle size is small. This is because the bulk density increases and a sufficient capacity cannot be obtained. Therefore, in this negative electrode material, by mixing the first carbon material having a large particle diameter and the second carbon material having a small particle diameter, the energy density is increased by the first carbon material, and the second carbon material Conductivity is ensured by the material.

  Examples of the first carbon material include pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, activated carbon, and non-graphitizable carbon. Examples of coke include pitch coke, needle coke, and petroleum coke. The organic polymer compound sintered body refers to a carbonized material obtained by firing a polymer material such as phenols or furans at an appropriate temperature.

  Examples of the second carbon material include fibrous carbon and carbon black, and among them, fibrous carbon is preferable.

  The first carbon material is observed as the first peak located on the larger particle diameter in the cumulative volume particle size distribution curve, and the second carbon material is observed as the first peak located on the smaller particle diameter. Is done.

  The accumulated amount of passage of the second peak is preferably, for example, 1% or more and 15% or less, and the ratio (R2 / R1) of the particle diameter (R2) of the second peak to the particle diameter (R1) of the first peak is For example, it is preferably greater than 0 and less than or equal to 0.05. This is because the energy density can be increased and the deterioration of the cycle characteristics, particularly the cycle characteristics during discharge at a high load rate can be suppressed.

  The accumulated amount of the second peak passing through means a volume obtained by integrating the range from the position where the particle diameter is 0 μm to the particle diameter (R2) of the second peak in the particle size distribution diagram. Can be easily calculated from the number of particles (n) and the diameter (d) of one particle measured by laser light scattering.

  The particle diameter (R1) of the first peak is preferably in the range of 4 μm to 150 μm, for example, and the particle diameter (R2) of the second peak is in the range of 0.1 μm to 3 μm, for example. It is preferable. This is because a high effect can be obtained within this range.

  When fibrous carbon is used as the second carbon material, the average length is preferably, for example, 2 μm or more and 10 μm or less. If it is too short, the effect of securing conductivity is low, and if it is too long, fibrous carbon aggregates, and the effect of securing conductivity as the whole negative electrode material may be reduced.

  Moreover, it is preferable that the average width | variety of fibrous carbon is 0.05 micrometer or more and 0.50 micrometer or less, for example. If it is too small, the tensile strength may be reduced, and the negative electrode material may be cut by expansion. This is because the effect may be reduced.

  In this specification, the length of the fibrous carbon refers to the size in the major axis direction when observed with, for example, an SEM (Scanning electron microscope), and the width refers to the size in the minor axis direction. Say.

  In addition, these negative electrode materials should just obtain two peaks in the cumulative volume particle size distribution measurement, and the first carbon material and the second carbon material are not limited to being composed of one kind of carbon material, respectively. You may be comprised from the seed | species or more.

  Such a negative electrode material is used for a secondary battery as follows, for example.

  FIG. 1 shows a cross-sectional structure of a secondary battery using the negative electrode material according to the present embodiment. This secondary battery is a so-called cylindrical type, and is a wound electrode in which a strip-like positive electrode 21 and a strip-like negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. It has a body 20. 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 winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode 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 electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum or the like is connected to the positive electrode 21 of the spirally wound electrode 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 an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, 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, one or more positive electrode materials capable of inserting and extracting lithium, which is an electrode reactant, as a positive electrode active material, and carbon black or It is configured to contain a conductive agent such as graphite and a binder such as polyvinylidene fluoride.

Examples of the positive electrode material capable of inserting and extracting lithium include non-lithium-containing compounds such as TiS, MoS ₂ , NbSe ₂ , V ₂ O ₅ , V ₆ O ₁₃ , and MnO ₂ , or an interlayer containing lithium Examples thereof include a compound, a lithium composite oxide containing lithium and a transition metal, or a lithium phosphate compound. Among these, lithium composite oxide or lithium phosphate compound is preferable. This is because they can generate a high voltage and have a high density, so that the capacity can be increased.

As a lithium composite oxide, as a transition metal, cobalt (Co), nickel, manganese (Mn), iron, vanadium (V), titanium (Ti), chromium (Cr) and copper (Cu) What contains at least 1 type is preferable, and what contains at least 1 type in the group which consists of cobalt, nickel, manganese, iron, vanadium, and titanium is still more preferable. Among these, examples of the lithium composite oxide containing manganese include a spinel compound represented by the chemical formula Li _x Mn _{2 -y} M1 _y O ₄ . In the formula, M1 is iron, cobalt, nickel, copper, zinc (Zn), aluminum, tin (Sn), chromium, vanadium, titanium, magnesium (Mg), calcium (Ca), strontium (Sr), boron (B). Represents at least one selected from the group consisting of gallium (Ga), indium (In), silicon (Si) and germanium (Ge), and the values of x and y are 0.9 ≦ x and 0.01 ≦ y ≦, respectively. 0.5. Examples of the lithium composite oxide containing nickel include those represented by the chemical formula LiNi _1-z M2 _z O ₂ . In the formula, M2 represents at least one selected from the group consisting of iron, cobalt, manganese, copper, zinc, aluminum, tin, chromium, vanadium, titanium, magnesium, calcium, strontium, boron, gallium, indium, silicon, and germanium. , Z is 0.01 ≦ z ≦ 0.5. Specific examples of such a lithium composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Co _0.5 O _2, LiNi _0.5 Co _0.3 Mn _0.2 O _{2, and the} like.

Examples of the lithium phosphate compound include LiFePO ₄ or LiFe _0.5 Mn _0.5 PO ₄ .

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A having a pair of opposed surfaces. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the 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 negative electrode active material layer 22B is configured to include the negative electrode material according to the present embodiment as a negative electrode active material capable of inserting and extracting lithium, which is an electrode reactant, for example. The material layer 21B includes the same binder as that of the material layer 21B. As a result, high energy density can be obtained, and cycle characteristics, in particular, deterioration of cycle characteristics during discharge at a high load rate can be suppressed.

  The separator 23 is made of, for example, 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, and these two or more kinds of porous films are laminated. It may be made the structure.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. The electrolytic solution includes, for example, a solvent and a lithium salt that is an electrolyte salt dissolved in the solvent. The solvent dissociates the electrolyte salt. Examples of the solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, sulfolane, acetonitrile, diethyl carbonate, dimethyl carbonate, and dipropyl carbonate. Any one or two or more of these may be used as a mixture.

Examples of the lithium salt include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiCl, or LiBr, and any one of these. 1 type (s) or 2 or more types are used in mixture.

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

  First, for example, a positive electrode material capable of inserting and extracting lithium, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is mixed with N-methyl-2-pyrrolidone or the like. To make a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, 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, and the positive electrode 21 is manufactured.

  Further, for example, the negative electrode material according to the present embodiment and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a paste. Negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 22A and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured.

  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 wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, an 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 through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte. On the other hand, when discharging is performed, for example, lithium ions are separated from the negative electrode 22 and inserted into the positive electrode 21 through the electrolyte. Here, the negative electrode 22 has a first peak and a second peak in the cumulative volume particle size distribution curve, the accumulated amount of passage of the second peak is 1% or more and 15% or less, and the particle diameter (R2) of the first peak Since the ratio of the second peak particle diameter (R1) to (the second peak particle diameter / the first peak particle diameter) is greater than 0 and less than or equal to 0.05, it includes two or more carbon materials. High energy density can be obtained. In addition, a decrease in conductivity is suppressed, and a decrease in cycle characteristics is suppressed even at a high load rate.

  As described above, according to the negative electrode material of the present embodiment, the accumulated amount of the second peak having a small particle size in the cumulative volume particle size distribution curve is 1% or more and 15% or less, and the particle size of the first peak having a large particle size is set. Since the ratio of the particle diameter (R2) of the second peak to (R1) is greater than 0 and less than or equal to 0.05, for example, the battery capacity can be increased, conductivity can be ensured, and high load Even if it is a discharge of a rate, the fall of cycling characteristics can be suppressed.

  In particular, when the negative electrode material contains fibrous carbon having an average length of 2 μm to 10 μm and an average width of 0.05 μm to 0.5 μm, a high effect can be obtained.

  Furthermore, specific embodiments of the present invention will be described in detail with reference to FIGS.

(Examples 1-1 to 1-4, 2-1 to 2-4)
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 material was obtained. Next, 91% by mass of this lithium-cobalt composite oxide, 6% by mass of graphite as a conductive agent, and 3% 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 the positive electrode current collector 21A made of a strip-shaped aluminum foil and dried. The positive electrode active material layer 21B was formed by compression molding with a press machine, and the positive electrode 21 was produced. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

In addition, after introducing a functional group containing oxygen into petroleum pitch within a range of 10% by mass or more and 20% by mass or less (so-called oxygen cross-linking), the first carbon material is fired at 1000 ° C. in an inert gas stream. As a result, a soft graphite carbon material having properties similar to glassy carbon was obtained. As a result of X-ray diffraction measurement of this material, the (002) plane spacing was 0.376 nm. The true specific gravity was 1.58 g / cm ³ . Furthermore, fibrous carbon as the second carbon material is generated directly from the gas phase by utilizing the catalytic effect of thermal decomposition of hydrocarbons and fine metal particles by CVD (Chemical Vapor deposition) method. I let you. In addition, the average length of the fibrous carbon measured by SEM was 6 μm, and the average width was 0.25 μm.

  Furthermore, the obtained soft graphite carbon material was used as a first carbon material, and fibrous carbon was mixed as a second carbon material at a predetermined ratio to obtain a negative electrode material. At that time, the average particle diameter of the soft graphite carbon was changed, and the ratio (R2 / R1) of the particle diameter (R2) of the second peak to the particle diameter (R1) of the first peak was changed to Examples 1-1 to 1- In Example 4, it was 0.02, and in Examples 2-1 to 2-4, it was 0.05. The mixing ratio of the soft graphite carbon material to the fibrous carbon is 1.0% for the passage of the second peak in Examples 1-1 to 1-4, 2-1 to 2-4, and 2%, respectively. 0.0%, 5.0%, and 10.0%. These were measured with a Microtrac particle size analyzer.

  A negative electrode mixture was prepared by mixing 90% by mass of the obtained negative electrode material and 10% by mass of polyvinylidene fluoride as a binder. Next, the negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, and then uniformly applied to both surfaces of the negative electrode current collector 22A made of a strip-shaped copper foil and dried. Then, the negative electrode active material layer 22B was formed by compression molding with a roll press machine, and the negative electrode 22 was produced. Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22A.

  After each of the positive electrode 21 and the negative electrode 22 was prepared, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm was prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 were stacked in this order to form a spiral structure The wound electrode body 20 was produced by winding a number of times.

After producing the wound electrode body 20, the wound electrode 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 wound electrode body 20 was housed inside a nickel-plated iron battery can 11. After that, an electrolytic solution was injected into the battery can 11 by a reduced pressure method. As the electrolytic solution, a solution in which LiPF ₆ was dissolved at 1.0 mol / kg in a solvent in which propylene carbonate and diethyl carbonate were mixed in an equal volume was used.

  After injecting the electrolyte into the battery can 11, the battery lid 14 is caulked to the battery can 11 through the gasket 17 having the surface coated with asphalt, so that Examples 1-1 to 1-4 and 2-1 A cylindrical secondary battery having a diameter of 20 mm and a height of 50 mm was obtained for ˜2-4.

  As Comparative Examples 1-1 to 1-3 with respect to Examples 1-1 to 1-4 and 2-1 to 2-4, (R1 / R2) is set to 0.02, and the passing peak integration of the second peak is 0, respectively. 0.05%, 30.0%, 50.0%, except that a negative electrode material mixed was used, and as Comparative Examples 2-1 to 2-3, (R1 / R2) was set to 0.05 In addition, a soft graphite carbon material as Comparative Example 3-1 was used except that a negative electrode material mixed so that the accumulated amount of the second peak passed was 0.05%, 30.0%, and 50.0%, respectively. In addition, as Comparative Examples 4-1 to 4-7, (R1 / R2) is set to 0.10, and the passing peak integration of the second peak is 0.05% and 1.0%, respectively. , 2.0%, 5.0%, 10.0%, 30.0%, 50.0% Can, others A secondary battery was fabricated in the same manner as in Example 1-1～1-4,2-1～2-4.

  Examples 1-1 to 1-4, 2-1 to 2-4, and Comparative Examples 1-1 to 1-3, 2-1 to 2-3, 3-1, 4-1 to 4-7 For the secondary battery, the initial capacity ratio and the cycle characteristics due to discharge at a high load rate were determined. The results are shown in Table 1 and FIGS.

  The initial capacity ratio was determined as a capacity ratio when the initial capacity of Comparative Example 3 was set to 100. The initial capacity was set to 4.2 V at 23 ° C. and charged for 8 hours at a constant current of 500 mA (0.25 C), and then the battery voltage was set to 2. at a constant current of 500 mA (0.25 C). The calculation was performed until 75V was reached.

  Further, the capacity retention rate as the cycle characteristics was obtained as a ratio of the discharge capacity at the 300th cycle to the discharge capacity obtained at the second charge / discharge. That is, (discharge capacity at the 300th cycle / second discharge capacity) × 100 (%) was calculated. Charging / discharging was performed until the battery voltage reached 2.75 V at a constant current of 4000 mA (2C) after charging at a constant current of 2000 mA for 3 hours at 23 ° C. with the battery voltage set to 4.2 V.

  As can be seen from Table 1, FIG. 3 and FIG. 4, the integrated amount of passage of the second peak is 1% or more and 15% or less, and the particle diameter (R2) of the second peak with respect to the particle diameter (R1) of the first peak. According to Examples 1-1 to 1-4, 2-1 to 2-4 in which the ratio (R2 / R1) is greater than 0 and equal to or less than 0.05, Comparative Examples 1-1 to 1-1 that do not satisfy these conditions The initial capacity and the capacity maintenance rate of the cycle were higher than those of −3, 2-1 to 2-3, 3-1, 4-1 to 4-7.

  That is, it is made of a carbon material having a first peak with a large particle diameter and a second peak with a small particle diameter in the cumulative volume particle size distribution curve, and the accumulated amount of passage of the second peak is 1% or more and 15% or less, and the first By using a negative electrode material in which the ratio (R2 / R1) of the second peak particle size (R2) to the peak particle size (R1) is greater than 0 and 0.05 or less, a high capacity can be obtained. At the same time, it has been found that the cycle characteristics can be improved even with high load rate discharge.

(Examples 5-1 to 5-9)
The secondary battery was changed in the same manner as in Examples 1-1 to 1-4 except that the length and width of the fibrous carbon were changed and the accumulated amount of the second peak was 2.0% or 10%. Was made. The mass mixing ratio of fibrous carbon and soft graphite carbon is fibrous carbon: soft graphite carbon = 4: 96, and the particle diameter (R1) of the first peak in the cumulative volume particle size distribution curve is 50 μm and the second peak. The particle diameter (R2) was 1 μm. For these secondary batteries, the initial capacity, the initial capacity ratio, and the cycle characteristics by discharging at a high load rate were determined in the same manner as in Examples 1-1 to 1-4. The results are shown in Table 2. The initial capacity ratio was determined as a capacity ratio when the initial capacity of Comparative Example 3-1 was set to 100.

  As can be seen from Table 2, according to Examples 5-1 to 5-5, the length of the fibrous carbon is 2 μm or more and 10 μm or less, and the width is 0.05 μm or more and 0.50 μm or less. The capacity retention rate was higher than in Examples 5-6 to 5-9 that did not satisfy the above.

  That is, it has been found that it is effective to include a carbon material having an average length of 2 μm to 10 μm and an average width of 0.05 μm to 0.50 μm.

  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, 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. 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.

  In the above-described embodiments and examples, a cylindrical secondary battery having a winding structure has been described. However, the present invention relates to an elliptical or polygonal secondary battery having a winding structure, or a positive electrode. The present invention can be similarly applied to a secondary battery having a structure in which the negative electrode is folded or stacked. In addition, the present invention can also be applied to a so-called coin type, button type, or square type secondary battery. Moreover, not only a secondary battery but a primary battery is applicable.

  Further, in the above embodiment and examples, the case where lithium is used as the electrode reactant has been described. However, other Group 1A elements such as sodium (Na) or potassium (K), magnesium or calcium (Ca), etc. The present invention can also be applied to the case of using the 2A group element, other light metals such as aluminum, lithium, or alloys thereof, and the same effects can be obtained. At that time, a negative electrode material, a positive electrode material, a non-aqueous 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 which expands and represents a part of winding electrode body in the secondary battery shown in FIG. It is a figure showing the relationship between the ratio of the particle diameter (R2) of the 2nd peak with respect to the particle diameter (R1) of the 1st peak, the passing peak integration of the 2nd peak, and the initial capacity ratio. It is a figure showing the relationship between the ratio of the particle size (R2) of the second peak to the particle size (R1) of the first peak, the accumulated amount of passage of the second peak, and the capacity retention rate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding electrode body, 21 ... Positive electrode, 21A DESCRIPTION OF SYMBOLS ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active material layer, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead.

Claims (6)

A cumulative volume particle size distribution curve comprising a carbon material having a first peak with a large particle size and a second peak with a small particle size;
The accumulated amount of passage of the second peak is 1% or more and 15% or less, and the ratio of the particle diameter of the second peak to the particle diameter of the first peak (particle diameter of the second peak / particle diameter of the first peak) is 0. A negative electrode material characterized by being larger than 0.05.   The negative electrode material according to claim 1, wherein the carbon material includes fibrous carbon and other carbon materials.   2. The negative electrode material according to claim 1, comprising fibrous carbon having an average length of 2 μm to 10 μm and an average width of 0.05 μm to 0.5 μm. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode is made of a carbon material having a first peak with a large particle diameter and a second peak with a small particle diameter in a cumulative volume particle size distribution curve, and the accumulated amount of passage of the second peak is 1% or more and 15% or less, and A negative electrode material having a ratio of the second peak particle diameter to the first peak particle diameter (second peak particle diameter / first peak particle diameter) greater than 0 and less than or equal to 0.05 is included. battery.   The battery according to claim 4, wherein the negative electrode includes fibrous carbon and other carbon materials as a carbon material. 5. The battery according to claim 4, wherein the negative electrode includes fibrous carbon having an average length of 2 μm to 10 μm and an average width of 0.05 μm to 0.5 μm.

Images