JP5114847B2 - Non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Description

  The present invention relates to a nonaqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics and a method for producing the same.

  In recent years, in order to reduce the size and weight of electronic devices such as mobile communication devices, notebook personal computers, palmtop personal computers, integrated video cameras, portable playback devices, and cordless phones, they are small and have a large capacity. There is a need for a battery.

  Examples of batteries that are widely used as power sources for electronic devices include primary batteries such as alkaline manganese batteries, and secondary batteries such as nickel cadmium batteries and lead storage batteries. Among them, non-aqueous electrolyte secondary batteries that use lithium composite oxide for the positive electrode and carbonaceous materials that can be doped / undoped with lithium ions for the negative electrode are small and light, with high cell voltage and high energy density. It is attracting attention because it can be obtained.

  When the non-aqueous electrolyte secondary battery having such a configuration is repeatedly charged and discharged, the capacity gradually decreases and the operation time of the electronic device becomes shorter. Improvement is demanded.

  For this reason, a method of performing charge / discharge control in accordance with the impedance ratio of the positive electrode and the negative electrode has been studied as a method for improving the charge / discharge cycle characteristics. For example, in Patent Document 1 below, in an electrochemical cell using lithium metal as a reference electrode as a counter electrode, the impedances of the positive electrode and the negative electrode are measured, and the reference electrode is used as a standard according to the impedance ratio between the positive electrode and the negative electrode. Describes a method for controlling the charging potential of the positive electrode and the negative electrode.

Japanese Patent Laid-Open No. 2002-50407

  However, as described in Patent Document 1 described above, the impedance of the positive electrode and the negative electrode measured with reference to the reference electrode and the actual impedance of the positive electrode and the negative electrode are not necessarily due to differences in battery configuration and assembly processes. It is possible that they do not match.

  Moreover, although the impedance of the positive electrode and the negative electrode largely depends on the specific surface area of the active material of each electrode, conventionally, the specific surface area of the active material of the positive electrode and the negative electrode has been considered independently.

  Therefore, it is difficult to accurately measure the impedance by the conventional method, and the specific surface areas of the active material of the positive electrode and the negative electrode are considered independently, so that the charge / discharge cycle characteristics can be sufficiently improved. There was a problem that could not.

  Moreover, in patent document 1, since it is necessary to insert a reference electrode in a battery in order to improve charging / discharging cycling characteristics, there also existed a problem that it was difficult to apply to a small battery.

  Accordingly, an object of the present invention is to provide a nonaqueous electrolyte secondary battery that can be easily applied to a small battery and that has improved charge / discharge cycle characteristics, and a method for manufacturing the same.

In order to solve the above-described problems , the present invention provides a negative electrode active material layer having a negative electrode active material layer formed on both sides of the negative electrode current collector and a positive electrode active material layer on both sides of the positive electrode current collector. Adjusting the specific surface area ratio S2 / S1 with the specific surface area S2 of the positive electrode active material of the positive electrode to be formed within a range of 0.5 ≦ S2 / S1 ≦ 4, and assembling the nonaqueous electrolyte secondary battery; The impedance of the positive electrode and the negative electrode in a state where the charging rate of the nonaqueous electrolyte secondary battery is 100% is measured, and the impedance between the absolute value Z1 of the imaginary component in the impedance at a frequency of 100 Hz and the absolute value Z2 of the imaginary component in the impedance at a frequency of 5 Hz. It is determined whether or not the ratio Z2 / Z1 is within the range of 0.2 ≦ Z2 / Z1 ≦ 1, and when the impedance ratio Z2 / Z1 is within the range, it is determined as a non-defective product. , If the impedance ratio Z2 / Z1 is outside the range is a method for fabricating a nonaqueous electrolyte secondary battery characterized by comprising a step of determining as defective.

As described above, in the present invention, the specific surface area ratio S2 / S1 between the specific surface area S1 of the negative electrode active material and the specific surface area S2 of the positive electrode active material is in the range of 0.5 ≦ S2 / S1 ≦ 4, and the charging rate The impedance ratio Z2 / Z1 between the absolute value Z1 of the imaginary component of the impedance at a frequency of 100 Hz and the absolute value Z2 of the imaginary component of the impedance at a frequency of 5 Hz in a state of 100% is in the range of 0.2 ≦ Z2 / Z1 ≦ 1. Therefore, deterioration of the positive electrode and the negative electrode can be suppressed.

  The present invention makes it possible to obtain a non-aqueous electrolyte secondary battery with improved charge / discharge cycle characteristics because the specific surface area ratio of the positive and negative electrode active materials and the impedance ratio of the positive and negative electrodes are within the specified range. There is an effect that can be.

  In addition, since the present invention can improve charge / discharge cycle characteristics without using a reference electrode, there is an effect that it can be easily applied to a small battery.

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

  FIG. 1 shows a configuration of an example of a nonaqueous electrolyte secondary battery according to a first embodiment of the present invention. This non-aqueous electrolyte secondary battery is formed by housing the battery element 10 in an exterior material 1 made of a moisture-proof laminate film and sealing the periphery of the battery element 10 by welding. The battery element 10 is provided with a positive electrode lead 3 and a negative electrode lead 4, and these leads are sandwiched by the outer packaging material 1 and drawn out to the outside. Both surfaces of the positive electrode lead 3 and the negative electrode lead 4 are coated with a resin piece 5 and a resin piece 6 in order to improve the adhesion to the exterior material 1.

[Exterior material]
The exterior material 1 has, for example, a laminated structure in which an adhesive layer, a metal layer, and a surface protective layer are sequentially laminated. The adhesive layer is made of a polymer film. Examples of the material constituting the polymer film include polypropylene (PP), polyethylene (PE), unstretched polypropylene (CPP), linear low density polyethylene (LLDPE), and low density. A polyethylene (LDPE) is mentioned. The metal layer is made of a metal foil, and an example of a material constituting the metal foil is aluminum (Al). Moreover, it is also possible to use metals other than aluminum as a material which comprises metal foil. Examples of the material constituting the surface protective layer include nylon (Ny) and polyethylene terephthalate (PET). The surface on the adhesive layer side is a storage surface on the side where the battery element 10 is stored.

[Battery element]
Hereinafter, the configuration of the battery element 10 will be described. FIG. 2 shows an enlarged part of the battery element 10 shown in FIG. For example, as shown in FIG. 2, the battery element 10 includes a strip-shaped negative electrode 13 having a gel electrolyte layer 15 provided on both sides, a separator 14, and a strip-shaped positive electrode 12 having a gel electrolyte layer 15 provided on both sides. The battery element 10 is a wound type battery element 10 that is formed by laminating the separator 14 and wound in the longitudinal direction. In addition to the first embodiment described above, for example, the battery element 10 may be composed of only a non-aqueous electrolyte without using a gel electrolyte. Furthermore, an embodiment such as a square battery in which similar battery elements are housed in a metal case instead of a laminate film is also possible.

[Positive electrode]
The positive electrode 12 includes a strip-shaped positive electrode current collector 12A and a positive electrode active material layer 12B formed on both surfaces of the positive electrode current collector 12A. The positive electrode current collector 12A is a metal foil made of, for example, aluminum (Al).

The positive electrode active material layer 12B includes, for example, a positive electrode active material, a conductive agent, and a binder. As the positive electrode active material, known positive electrode active material materials that can be doped / undoped with lithium ions can be used, and are not particularly limited, but various oxides such as manganese dioxide, lithium manganese composite oxide, lithium-containing nickel Examples thereof include oxides, lithium-containing cobalt oxides, lithium-containing nickel cobalt oxides, lithium-containing iron oxides, vanadium oxides containing lithium, and chalcogen compounds such as titanium disulfide and molybdenum disulfide. Among them, when a lithium-containing cobalt oxide (for example, LiCoO ₂ ), a lithium-containing nickel cobalt oxide (for example, LiNi _0.8 Co _0.2 O ₂ ), or a lithium manganese composite oxide (for example, LiMn ₂ O ₄ , LiMnO ₂ ) is used. This is preferable because a high voltage can be obtained. As the positive electrode active material, one kind of oxide may be used alone, or two or more kinds of oxides may be mixed and used.

  Note that, as the positive electrode active material, a plurality of the above-described positive electrode active materials can be mixed and used.

  The conductive agent is not particularly limited as long as an appropriate amount can be mixed with the positive electrode active material to impart conductivity, and for example, a carbon material such as carbon black or graphite is used. As the binder, a known binder that is usually used in a positive electrode mixture of this type of battery can be used, and preferably polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, etc. A fluorine resin is used.

  One end of the positive electrode 12 in the longitudinal direction is provided with a positive electrode lead 3 connected by spot welding or ultrasonic welding, for example. The positive electrode lead 3 is preferably a metal foil or a net-like one, but there is no problem even if it is not a metal as long as it is electrochemically and chemically stable and can conduct electricity. As a material of the positive electrode lead 3, for example, a metal such as aluminum can be used.

[Negative electrode]
The negative electrode 13 includes a strip-shaped negative electrode current collector 13A and a negative electrode active material layer 13B formed on both surfaces of the negative electrode current collector 13A. As the negative electrode current collector 13A, the negative electrode current collector 13A is made of, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 13B includes, for example, a negative electrode active material, a conductive agent if necessary, and a binder. As the negative electrode active material, a carbon material, crystalline, or amorphous metal oxide that can be doped / undoped with lithium is used. Specifically, examples of the carbon material that can be doped / dedoped with lithium include graphite, non-graphitizable carbon material, graphitizable carbon material, and highly crystalline carbon material with a developed crystal structure. More specifically, pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke), graphites, glassy carbons, organic polymer compound fired bodies (phenolic resin, furan resin, etc.) at an appropriate temperature. Baked and carbonized), carbon fibers, activated carbon, carbon materials such as carbon black, polymers such as polyacetylene, and the like can be used.

As another negative electrode active material, a metal capable of forming an alloy with lithium, or an alloy compound of such a metal can be given. Specifically, the alloy compound referred to here is M _p M ′ _q Li _r (where M ′ is 1 other than Li element and M element), where M is a metal element capable of forming an alloy with lithium. And p is a numerical value greater than 0, and q and r are numerical values greater than or equal to 0). Furthermore, in the present invention, elements such as B, Si, As and the like, which are semiconductor elements, are also included in the metal element, specifically, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga). , Indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn) , Hafnium (Hf), zirconium (Zr), yttrium (Y) and their alloy compounds, for example, Li-Al, Li-Al-M (wherein M is a group 2A, 3B, 4B) It consists of one or more transition metal elements.), AlSb, CuMgSb and the like.

Among the elements described above, it is preferable to use a group 3B typical element as an element capable of forming an alloy with lithium. Among them, it is preferable to use an element such as Si or Sn or an alloy thereof, and Si or Si alloy is particularly preferable. Specifically, the Si alloy or the Sn alloy is a compound represented by M _x Si, M _x Sn (wherein M is one or more metal elements excluding Si or Sn), specifically, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi _{2 and the} like.

Furthermore, a 4B group compound excluding carbon containing one or more nonmetallic elements can also be used as the negative electrode material of the present invention. Two or more types of 4B group elements may be contained in the negative electrode material. Moreover, metal elements other than the 4B group containing lithium may be contained. For example, SiC, Si ₃ N ₄ , Si ₂ N ₂ O, Ge ₂ N ₂ O, SiO _x (0 <x ≦ 2), SNO _x (0 <x ≦ 2), LiSiO, LiSNO, and the like.

  The conductive agent is not particularly limited as long as an appropriate amount can be mixed with the positive electrode active material to impart conductivity, and for example, a carbon material such as carbon black or graphite is used. As the binder, for example, polyvinylidene fluoride, styrene butadiene rubber or the like is used.

  Further, similarly to the positive electrode 12, the negative electrode lead 4 connected by, for example, spot welding or ultrasonic welding is also provided at one end in the longitudinal direction of the negative electrode 13. The negative electrode lead 4 is electrochemically and chemically stable, and there is no problem even if it is not a metal as long as it can conduct electricity. As a material of the negative electrode lead 4, for example, copper (Cu), nickel (Ni) or the like can be used.

[Electrolytes]
The gel electrolyte layer 15 includes an electrolytic solution and a polymer compound that serves as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 15 is preferable because it can obtain high ionic conductivity and prevent battery leakage.

  As the electrolytic solution, a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent can be used. As the non-aqueous solvent, for example, it is preferable to contain at least one of ethylene carbonate and propylene carbonate. This is because the cycle characteristics can be improved. In particular, it is preferable to mix and contain ethylene carbonate and propylene carbonate because cycle characteristics can be further improved. The nonaqueous solvent preferably contains at least one of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, or methyl propyl carbonate. This is because the cycle characteristics can be further improved.

  The non-aqueous solvent preferably further contains at least one of 2,4-difluoroanisole and vinylene carbonate. This is because 2,4-difluoroanisole can improve discharge capacity, and vinylene carbonate can further improve cycle characteristics. In particular, it is more preferable that they are mixed and contained because both the discharge capacity and the cycle characteristics can be improved.

  Non-aqueous solvents further include butylene carbonate, γ-butyrolactone, γ-valerolactone, those in which part or all of the hydrogen groups of these compounds are substituted with fluorine groups, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide or trimethyl phosphate may be included. Yes.

  Depending on the electrode to be combined, the reversibility of the electrode reaction may be improved by using a material in which part or all of the hydrogen atoms of the substance contained in the non-aqueous solvent group are substituted with fluorine atoms. Therefore, these substances can be used as appropriate.

Examples of the lithium salt that is an electrolyte salt include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) _2. , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBF ₂ (ox), LiBOB, or LiBr are suitable, and one or more of these are used in combination. be able to. Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

  Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, from the viewpoint of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable.

[Separator]
The separator 14 is composed of, for example, a porous film made of a polyolefin-based material such as polypropylene (PP) or polyethylene (PE), or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated. Among these, polyethylene and polypropylene porous films are the most effective.

  In general, the thickness of the separator 14 is preferably 5 to 50 μm, more preferably 7 to 30 μm. When the separator 14 is too thick, the filling amount of the active material is reduced to reduce the battery capacity, and the ionic conductivity is reduced to deteriorate the current characteristics. On the other hand, if the film is too thin, the mechanical strength of the film decreases.

[Preparation of non-aqueous electrolyte secondary battery]
Next, a method for manufacturing a nonaqueous electrolyte secondary battery according to the first embodiment of the present invention will be described. First, the positive electrode 12 is produced. The above-mentioned positive electrode active material, binder, and conductive agent are uniformly mixed to form a positive electrode mixture, and this positive electrode mixture is dispersed in a solvent and, if necessary, in a slurry state by a ball mill, a sand mill, a twin-screw kneader, etc. To. The solvent is not particularly limited as long as it is inert with respect to the electrode material and can dissolve the binder, and any of inorganic solvents and organic solvents can be used. For example, N-methyl- 2-pyrrolidone (NMP) or the like is used. Note that the positive electrode active material, the conductive agent, the binder, and the solvent only need to be uniformly dispersed, and the mixing ratio is not limited. Next, this slurry is uniformly applied to both surfaces of the positive electrode current collector 12A by a doctor blade method or the like. At that time, the specific surface area of the positive electrode active material, for example, when adjusted to be within a range of about 0.1m ² /g~0.8m ² / g preferred. Furthermore, after drying at a high temperature to drive off the solvent, the positive electrode active material layer 12B is formed, for example, by compression molding with a roll press. Thereby, the positive electrode 12 is produced.

Next, the negative electrode 13 is produced. The above-described negative electrode active material, binder, and conductive agent are uniformly mixed to form a negative electrode mixture, which is dispersed in a solvent to form a slurry. At this time, a ball mill, a sand mill, a biaxial kneader or the like may be used as in the case of the positive electrode mixture. As the solvent, for example, N-methyl-2-pyrrolidone, methyl ethyl ketone, or the like is used. Note that the mixing ratio of the negative electrode active material, the conductive agent, the binder, and the solvent is not limited as in the case of the positive electrode active material. Next, this slurry is uniformly applied to both surfaces of the negative electrode current collector 13A by a doctor blade method or the like. At that time, the specific surface area of the negative electrode active material, for example, when adjusted to be within a range of about 0.2m ² /g~0.7m ² / g preferred. Furthermore, after drying at a high temperature to drive off the solvent, the negative electrode active material layer 13B is formed, for example, by compression molding with a roll press. Thereby, the negative electrode 13 is produced.

  The coating apparatus is not particularly limited, and slide coating, extrusion type die coating, reverse roll, gravure, knife coater, kiss coater, micro gravure, rod coater, blade coater and the like can be used. Also, the drying method is not particularly limited, but standing drying, blower dryer, hot air dryer, infrared heater, far infrared heater, and the like can be used.

  A gel electrolyte layer 15 is prepared by applying a precursor solution containing a solvent, an electrolyte salt, a polymer compound, and a mixed solvent to each of the positive electrode 12 and the negative electrode 13 manufactured as described above, and volatilizing the mixed solvent. Form. The positive electrode lead 3 is attached to the end of the positive electrode current collector 12A in advance by welding, and the negative electrode lead 4 is attached to the end of the negative electrode current collector 13A in advance by welding.

  Next, the positive electrode 12 and the negative electrode 13 on which the gel electrolyte layer 15 is formed are laminated via a separator 14 to form a laminated body, and then the laminated body is wound in the longitudinal direction thereof to form a wound battery element 10. Form.

  Next, the exterior material 1 made of a laminate film is deep-drawn to form a recess 2, the battery element 10 is inserted into the recess 2, an unprocessed portion of the exterior material 1 is folded back onto the recess 2, and the recess 2 The outer peripheral part of is thermally welded and sealed. As described above, the nonaqueous electrolyte secondary battery according to the embodiment of the present invention is manufactured.

[Measurement of impedance]
Next, the AC impedance of the positive electrode and the negative electrode of the nonaqueous electrolyte secondary battery manufactured as described above is measured. First, the AC impedance of the battery in a predetermined frequency range is measured. Measurement equipment such as a potentio / galvanostat or a frequency response analyzer is used to measure the AC impedance of the battery.

  When the AC impedance of the nonaqueous electrolyte secondary battery is measured in this way, the value of the AC impedance at each frequency is a value obtained by combining the impedances of the positive electrode 12 and the negative electrode 13 because there is no reference electrode serving as a reference. .

  However, since the positive electrode 12 and the negative electrode 13 usually have different electrode characteristics, the impedance response with respect to the frequency of only the positive electrode 12 or the negative electrode 13 is different. For example, the impedance due to the positive electrode 12 or the negative electrode 13 mainly appears at a predetermined frequency. .

  Therefore, the magnitude relationship between the impedances of the positive electrode 12 and the negative electrode 13 can be known by comparing the imaginary component depending on the frequency among the real component and the imaginary component of the impedance at a predetermined frequency. Since the impedance changes depending on the state of charge, the measurement is performed in a state where the charging rate is 100% with respect to the rated capacity.

  FIG. 3 is a graph showing an example of the relationship between the frequency of the nonaqueous electrolyte secondary battery according to the first embodiment of the present invention and the absolute value of the imaginary component of the impedance. As shown in FIG. 3, for example, there is a flat portion in the vicinity of the frequency of 100 Hz, and an impedance peak is seen in the vicinity of the frequency of 5 Hz. Therefore, the absolute value of the imaginary component of the impedance at these two frequencies is used as a reference. can do.

  In the case of this nonaqueous electrolyte secondary battery, the absolute value Z1 of the imaginary component of the impedance at a frequency of 100 Hz mainly indicates the impedance of the negative electrode 13, and the absolute value Z2 of the imaginary component of the impedance at a frequency of 5Hz is mainly the positive electrode 12. The impedance is shown, and by comparing Z1 and Z2, the magnitude relationship between the impedances of the positive electrode 12 and the negative electrode 13 of the battery can be known.

  Next, based on the negative electrode impedance Z1 and the positive electrode impedance Z2 measured as described above, an impedance ratio Z2 / Z1 is calculated. And the quality of this nonaqueous electrolyte secondary battery is discriminate | determined according to whether impedance ratio Z2 / Z1 exists in the predetermined range. For example, when the impedance ratio Z2 / Z1 is within a predetermined range, the product is rejected, and when the impedance ratio Z2 / Z1 is outside the predetermined range, the product is rejected as a defective product.

  The value of the impedance ratio Z2 / Z1 is preferably in the range of 0.2 ≦ Z2 / Z1 ≦ 1, for example.

  For example, the quality of the nonaqueous electrolyte secondary battery may be determined as follows. That is, a measuring device that measures AC impedance is connected to a computer such as a PC (Personal Computer), and the absolute value of the imaginary component of the AC impedance measured by the measuring device is output to the computer. Then, the computer determines whether the absolute value of the imaginary component of the AC impedance supplied from the measuring device is within a predetermined range, and if the absolute value of the imaginary component of the AC impedance is within the predetermined range, For example, a non-defective product is displayed on a display unit such as a monitor connected to the computer. On the other hand, when the absolute value of the imaginary component of the AC impedance is outside the predetermined range, for example, the display unit displays that the product is defective.

  Next, the charge / discharge cycle characteristics in the nonaqueous electrolyte secondary battery according to the first embodiment of the present invention will be described. The nonaqueous electrolyte secondary battery according to the first embodiment of the present invention has a charge / discharge cycle by adjusting the specific surface area ratio between the negative electrode active material and the positive electrode active material and the impedance ratio between the negative electrode 13 and the positive electrode 12. Characteristics can be improved.

  The specific surface areas of the positive electrode 12 and the negative electrode 13 need to be balanced to some extent. For example, when the specific surface area of one of the positive electrode 12 and the negative electrode 13 is very large compared to the other, the efficiency of lithium exchange between the positive and negative electrodes is deteriorated.

  The impedance of the positive electrode 12 and the negative electrode 13 depends on the specific surface area of the active material of the positive electrode 12 and the negative electrode 13. Usually, when the specific surface area of the active material is large, the impedance is small, and when the specific surface area is small, the impedance is large. Therefore, in order to improve the charge / discharge cycle characteristics, it is necessary to make the impedance ratio fall within a predetermined range.

  Therefore, in order to improve the charge / discharge cycle characteristics, the specific surface area ratio of the active material in the positive electrode 12 and the negative electrode 13 needs to be within a predetermined range, and the impedance ratio needs to be within a predetermined range. There is.

  In the case of this non-aqueous electrolyte secondary battery, specifically, for example, when the specific surface area ratio S2 / S1 is smaller than 0.5 and the impedance ratio Z2 / Z1 is larger than 1, the impedance of the positive electrode 12 is negative. Since the impedance is greater than 13, impedance of the positive electrode 12 is deteriorated and charge / discharge cycle characteristics are deteriorated.

  On the other hand, for example, when the specific surface area ratio S2 / S1 is larger than 4 and the impedance ratio Z2 / Z1 is smaller than 0.2, since the impedance of the negative electrode 13 is extremely larger than the impedance of the positive electrode 12, the negative electrode 13 Deterioration occurs, and the charge / discharge cycle characteristics deteriorate.

  Accordingly, in this case, the specific surface area of the active material of the positive electrode and the negative electrode is controlled so that the specific surface area ratio S2 / S1 is 0.5 ≦ S2 / S1 ≦ 4, and the impedance ratio Z2 / Z1 is 0.2 ≦ Z2. By controlling the impedance so that / Z1 ≦ 1, a non-aqueous electrolyte secondary battery having good charge / discharge cycle characteristics can be obtained. In addition, by determining whether the impedance ratio of the positive electrode 12 and the negative electrode 13 is within the above-described range, it is simply determined whether the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery are good. be able to.

  Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a cross-sectional view showing a configuration of an example of a nonaqueous electrolyte secondary battery according to the second embodiment of the present invention. This non-aqueous electrolyte secondary battery is a so-called cylindrical shape, and a strip-shaped positive electrode 32 and a strip-shaped negative electrode 33 are disposed opposite to each other with a separator 34 inside a substantially hollow cylindrical battery can 31. The wound battery element 50 is included. The battery can 31 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 31, an electrolytic solution which is a liquid electrolyte is injected and impregnated in the separator 34. In addition, a pair of insulating plates 35 and 36 are arranged perpendicular to the winding peripheral surface so as to sandwich the battery element 50.

  At the open end of the battery can 31, a battery lid 37, a safety valve mechanism 38 provided inside the battery lid 37 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 39 are interposed via a gasket 40. It is attached by caulking, and the inside of the battery can 31 is sealed. The battery lid 37 is made of, for example, the same material as the battery can 31. The safety valve mechanism 38 is electrically connected to the battery lid 37 via a heat sensitive resistance element 39, and the disk plate 41 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 37 and the battery element 50 is cut off. The heat-sensitive resistor element 39 limits the current by increasing the resistance value when the temperature rises, and prevents abnormal heat generation due to a large current. The gasket 40 is made of, for example, an insulating material, and the surface is coated with asphalt.

  The battery element 50 is wound around the center pin 42, for example. A positive electrode lead 43 made of aluminum (Al) or the like is connected to the positive electrode 32 of the battery element 50, and a negative electrode lead 44 made of nickel or the like is connected to the negative electrode 33. The positive electrode lead 43 is electrically connected to the battery lid 37 by being welded to the safety valve mechanism 38, and the negative electrode lead 44 is welded to and electrically connected to the battery can 31.

  Hereinafter, the configuration of the battery element 50 accommodated in the battery can 31 will be described. FIG. 5 shows an enlarged part of the battery element 50 shown in FIG. Note that the material used for the positive electrode 32 and the positive electrode 33 and the separator 34 are the same as those in the first embodiment described above, and thus the description thereof is omitted.

[Positive electrode]
As shown in FIG. 5, the positive electrode 32 includes, for example, a positive electrode current collector 32A having a pair of opposed surfaces, and a positive electrode active material layer 32B provided on both surfaces of the positive electrode current collector 32A. In addition, you may make it have the area | region where the positive electrode active material layer 32B was provided only in the single side | surface of 32 A of positive electrode collectors. The positive electrode current collector 32A is made of, for example, a metal foil such as an aluminum (Al) foil, a nickel foil, or a stainless steel foil. Note that the material used for the positive electrode active material layer 32B is the same as that described in the first embodiment, and is omitted.

  One positive electrode lead 43 connected by spot welding or ultrasonic welding is welded to one end of the positive electrode 32. The positive electrode lead 43 is preferably a metal foil or a net-like one, but there is no problem even if it is not a metal as long as it is electrochemically and chemically stable and can conduct electricity. Examples of the material of the positive electrode lead 43 include Al. The positive electrode lead 43 is welded to the exposed portion of the positive electrode current collector provided at the end of the positive electrode 32.

[Negative electrode]
As shown in FIG. 5, the negative electrode 33 includes, for example, a negative electrode current collector 33A having a pair of opposed surfaces, and a negative electrode active material layer 33B provided on both surfaces of the negative electrode current collector 33A. In addition, you may make it have the area | region in which the negative electrode active material layer 33B was provided only in the single side | surface of 33 A of negative electrode collectors. The negative electrode current collector 33A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. Note that the material used for the negative electrode active material layer 33B is the same as that described in the first embodiment, and is omitted.

  One end of the negative electrode 33 has one negative electrode lead 44 connected by spot welding or ultrasonic welding. The negative electrode lead 44 is electrochemically and chemically stable and can be conductive so long as it is not a metal. Examples of the material of the negative electrode lead 44 include copper and nickel. Similarly to the positive electrode lead welded portion, the negative electrode lead 44 is welded to the exposed portion of the negative electrode current collector provided at the end of the negative electrode 33.

[Electrolytes]
The configuration of the electrolytic solution (that is, the liquid solvent, the electrolyte salt, and the additive) is the same as that in the first embodiment described above, and thus the details are omitted. As the electrolyte, a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent can be used. The nonaqueous electrolytic solution is prepared by appropriately combining a nonaqueous solvent and an electrolyte salt, and any organic solvent can be used as long as it is a material generally used for this type of battery.

[Production of non-aqueous electrolyte secondary battery]
Next, a method for manufacturing a cylindrical nonaqueous electrolyte secondary battery will be described. First, the positive electrode 32 and the negative electrode 33 are produced in the same manner as in the first embodiment. The produced positive electrode 32 and negative electrode 33 are laminated in the order of the positive electrode 32, the separator 34, the negative electrode 33, and the separator 34, and wound to obtain a battery element 50. At this time, the current collector exposed portions provided on the positive electrode 32 and the negative electrode 33 are laminated so as to be opposed to each other, and are stacked, and the battery element 50 has an outermost peripheral portion, an innermost peripheral portion, and an intermediate layer portion. The current collector facing surface is configured to have one or more rounds. When a solid or gel electrolyte is used, the electrolyte solution is uniformly applied to the surfaces of the positive electrode 32 and the negative electrode 33, dried in a room temperature or high temperature atmosphere, and the solvent is vaporized and removed to form an electrolyte layer. Thereafter, the battery element 50 is laminated with the separator 34 and wound.

  Next, the battery element 50 described above is accommodated in the battery can 31. At this time, the negative electrode lead outlet side of the winding surface of the battery element 50 is accommodated so as to be covered with the insulating plate 36 made of an insulating resin. Thereafter, one electrode rod is inserted from the center of the battery element winding, the other electrode rod is disposed outside the bottom surface of the battery can and resistance welding is performed, and the negative electrode lead 44 is welded to the battery can.

  After welding the negative electrode lead 44 and the battery can 31, the center pin 42 is inserted, and the insulating plate 35 is disposed also on the winding surface portion located at the open end of the battery can to inject the electrolyte. Further, the positive electrode lead 43 is connected to a battery lid 37 provided with a safety valve mechanism 38 and a PTC element 39 on the inner side, and the battery lid 7 is attached by caulking through an insulating sealing gasket 40, so that the inside of the battery can 31 is Is sealed.

  The positive electrode lead 43 needs to have a certain length in the manufacturing process. This is for sealing the open end of the battery can 31 after connecting the positive electrode lead 43 to the safety valve mechanism 38 provided in the battery lid 37 in advance. The shorter the positive electrode lead 43 is, the positive electrode lead 43 and the battery lid 37 are. Connection becomes difficult. For this reason, the positive electrode lead 43 is bent and accommodated in a substantially U shape inside the battery.

[Measurement of impedance]
Next, the impedance Z1 of the negative electrode and the impedance Z2 of the positive electrode of the nonaqueous electrolyte secondary battery manufactured as described above are measured. Then, based on the measured impedances Z1 and Z2, an impedance ratio Z2 / Z1 between the positive electrode and the negative electrode is calculated, and this non-water is determined depending on whether or not the value of the impedance ratio Z2 / Z1 is within a predetermined range. The quality of the electrolyte secondary battery is determined. The method for measuring the impedance and the impedance ratio is the same as that described in the first embodiment, and will not be described.

  Hereinafter, the nonaqueous electrolyte secondary battery according to the first embodiment of the present invention will be specifically described by way of examples. However, the first embodiment is limited to only these examples. is not.

Example 1
First, the positive electrode 12 was produced as follows. 91% by weight of LiCoO ₂ powder having an average particle diameter of 10 μm and a specific surface area S2 of 0.4 m ² / g, 6% by weight of graphite as a conductive agent, and polyvinylidene fluoride 3 as a binder A positive electrode mixture was prepared by mixing with wt%. This positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry, which was uniformly applied to one side of a 20 μm-thick strip-shaped aluminum foil serving as the positive electrode current collector 12A, and then dried. And positive electrode active material layer 12B was produced by compression molding with a roll press machine.

Next, the negative electrode 13 was produced as follows. A negative electrode mixture was prepared by mixing 90% by weight of graphite powder pulverized and adjusted to have a specific surface area S1 of 0.2 m ² / g and 10% by weight of polyvinylidene fluoride as a binder. This negative electrode mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry, which was uniformly applied to one side of a strip-shaped copper foil having a thickness of 20 μm to be the negative electrode current collector 13A, and then dried. And the negative electrode active material layer 13B was produced by compression molding with a roll press machine.

Moreover, the gel electrolyte was produced as follows. A plasticizer was prepared by mixing 13.0% by weight of ethylene carbonate (EC), 13.0% by weight of propylene carbonate (PC), and 4% by weight of LiPF _{6 as} an electrolyte salt. On the other hand, 10% by weight of block copolymer polyvinylidene fluoride-co-hexafluoropropylene having a molecular weight of 600,000 and 60% by weight of diethyl carbonate were mixed and dissolved. Next, this was uniformly applied and impregnated on one surface of the negative electrode active material layer 13B. Then, by standing for 8 hours at room temperature, diethyl carbonate was vaporized and removed, and a gel electrolyte was produced.

  Finally, as described above, the positive electrode active material layer 12B and the negative electrode active material layer 13B coated with the gel electrolyte were pressure-bonded with the surfaces coated with the gel electrolyte facing each other, and the battery element 10 was produced. . This power generation element was vacuum-sealed in a moisture-proof aluminum laminate film exterior having a thickness of 180 μm to produce a flat gel electrolyte battery having dimensions of approximately 2.5 cm × 4.0 cm × 0.46 mm.

Example 2
The same procedure as in Example 1 was conducted except that graphite powder pulverized and adjusted so that the specific surface area S1 was 0.3 m ² / g was used as the negative electrode active material.

Example 3
The same procedure as in Example 1 was conducted except that graphite powder pulverized and adjusted so that the specific surface area S1 was 0.7 m ² / g was used as the negative electrode active material.

Example 4
LiCoO ₂ powder having an average particle diameter of 6 μm and a specific surface area S2 of 0.8 m ² / g is used as a positive electrode active material, and pulverized so that the specific surface area S1 is 0.3 m ² / g. Except for using the prepared graphite powder as the negative electrode active material, the same procedure as in Example 1 was performed.

Example 5
Except that LiCoO ₂ powder having an average particle diameter of 20 μm and a specific surface area S2 of 0.1 m ² / g was used as the positive electrode active material, the same procedure as in Example 1 was performed.

Example 6
The same as Example 1 except that LiNi _0.33 Co _0.33 Mn _0.33 O ₂ powder having an average particle diameter of 10 μm and a specific surface area S2 of 0.8 m ² / g was used as the positive electrode active material. did.

Example 7
50.0% by weight of LiCoO ₂ powder having an average particle diameter of 10 μm and a specific surface area of 0.4 m ² / g, an average particle diameter of 10 μm and a specific surface area of 0.8 m ² / g Except for using as a positive electrode active material a powder having a specific surface area S2 of 0.6 m ² / g mixed with 50.0 wt% of LiNi _0.33 Co _0.33 Mn _0.33 O ₂ powder of Example 1 All were the same.

Comparative Example 1
The same procedure as in Example 1 was conducted except that graphite powder pulverized and adjusted so that the specific surface area S1 was 1.0 m ² / g was used as the negative electrode active material.

Comparative Example 2
LiCoO ₂ powder having an average particle diameter of 6 μm and a specific surface area S2 of 0.8 m ² / g is used as the positive electrode active material, and pulverized so that the specific surface area S1 is 0.15 m ² / g. Except for using the prepared graphite powder as the negative electrode active material, the same procedure as in Example 1 was performed.

Comparative Example 3
LiCoO ₂ powder having an average particle diameter of 6 μm and a specific surface area S2 of 0.8 m ² / g is used as the positive electrode active material, and pulverized so that the specific surface area S1 is 0.18 m ² / g. A battery was fabricated in the same manner as in Example 1 except that the adjusted graphite powder was used as the negative electrode active material.

<Measurement of AC impedance>
The non-aqueous electrolyte secondary batteries produced as shown in the above-mentioned Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to constant current and constant voltage charging at 0.2 C, 10 H, 4.2 V, and rated capacity. The charging rate was 100%. Next, in a state where the AC impedance of the battery is controlled at a constant voltage with respect to the battery voltage, the AC impedance is measured using a potentio / galvanostat and a frequency response analyzer under the conditions of a frequency of 10,000 to 0.1 Hz and an amplitude of 5 mV. Went. Then, the absolute value of the imaginary component was obtained from the impedance values at frequencies of 100 Hz and 5 Hz, and the absolute value Z1 of the imaginary component of the impedance of frequency 100 Hz and the absolute value Z2 of the imaginary component of the impedance of frequency 5 Hz were obtained.

<Charge / discharge cycle characteristics>
Charge / discharge cycle in which the battery whose AC impedance was measured was discharged at 0.2C to a final voltage of 3.0V, charged at a constant current and constant voltage at 2.5C and 4.2V at 1C, and discharged to a final voltage of 3.0V at 1C. The test was conducted for 500 cycles. Then, the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle was calculated as the capacity maintenance rate, and the capacity maintenance rate at this time was 80%, which was used as a criterion for the pass / fail judgment.

  For the batteries of Examples 1 to 7 and Comparative Examples 1 to 3 manufactured as described above, the specific surface area ratio S2 / S1 between the positive electrode active material and the negative electrode active material, the value of the imaginary component of the AC impedance at a frequency of 100 Hz Table 1 shows the ratio Z2 / Z1 between the absolute value Z1 and the absolute value of the imaginary component value of the AC impedance at 5 Hz, and the calculation result of the capacity retention rate at 500 cycles.

  From these results, in Examples 1 to 7, the capacity retention ratio can be set to 80% or more by adjusting the specific surface area ratio S2 / S1 and the impedance ratio Z2 / Z1 so that both are within the specified range. .

  On the other hand, in Comparative Examples 1 and 2, when the specific surface area ratio S2 / S1 and the impedance ratio Z2 / Z1 are both out of the specified range, the capacity retention ratio becomes less than 80%. Further, as in Comparative Example 3, by adjusting the impedance ratio Z2 / Z1 so as to be within a specified range and setting the specific surface area ratio S2 / S1 to be out of the specified range, the capacity retention ratio is 80. %.

  From the above results, in order to make the capacity maintenance ratio 80% or more, the specific surface area ratio S2 / S1 is in the range of 0.5 ≦ S2 / S1 ≦ 4, and the impedance ratio Z2 / Z1 is 0.00. It turns out that it needs to be in the range of 2 ≦ Z2 / Z1 ≦ 1.

  Although the first and second embodiments of the present invention have been described above, the present invention is not limited to the first and second embodiments of the present invention described above, and the gist of the present invention is described. Various modifications and applications are possible without departing from the scope. For example, the numerical values given in the first and second embodiments described above are merely examples, and different numerical values may be used as necessary.

  In addition, the shape of the nonaqueous electrolyte secondary battery is not limited to the shape in the first and second embodiments described above, and can be applied to various shapes of batteries such as a coin type and a button type. is there.

It is a perspective view which shows the structure of an example of the nonaqueous electrolyte secondary battery by 1st Embodiment of this invention. It is the basic diagram which expanded a part of battery element of the nonaqueous electrolyte secondary battery by 1st Embodiment of this invention. It is a basic diagram which shows the relationship between the frequency of the nonaqueous electrolyte secondary battery by 1st Embodiment of this invention, and the absolute value of the imaginary component of an impedance. It is sectional drawing which shows the structure of an example of the nonaqueous electrolyte secondary battery by the 2nd Embodiment of this invention. It is the basic diagram which expanded a part of battery element of the nonaqueous electrolyte secondary battery by the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior material 2 Recess 3 Positive electrode lead 4 Negative electrode lead 5 Resin piece 6 Resin piece 10 Battery element 12 Positive electrode 12A Positive electrode current collector 12B Positive electrode active material layer 13 Negative electrode 13A Negative electrode current collector 13B Negative electrode active material layer 14 Separator 15 Gel electrolyte layer 31 battery can 32 positive electrode 32A positive electrode current collector 32B positive electrode active material layer 33 negative electrode 33A negative electrode current collector 33B negative electrode active material layer 50 battery element

Claims (1)

The specific surface area S1 of the negative electrode active material in which the negative electrode active material layer is formed on both sides of the negative electrode current collector and the specific surface area S2 of the positive electrode active material in which the positive electrode active material layer is formed on both sides of the positive electrode current collector Adjusting the specific surface area ratio S2 / S1 within the range of 0.5 ≦ S2 / S1 ≦ 4, and assembling the nonaqueous electrolyte secondary battery;
The impedance of the positive electrode and the negative electrode in a state where the charging rate of the assembled nonaqueous electrolyte secondary battery is 100% is measured, and the absolute value Z1 of the imaginary component in the impedance at a frequency of 100 Hz and the absolute value Z2 of the imaginary component in the impedance at a frequency of 5 Hz. It is determined whether or not the impedance ratio Z2 / Z1 is within the range of 0.2 ≦ Z2 / Z1 ≦ 1, and when the impedance ratio Z2 / Z1 is within the range, it is determined as a non-defective product, And a step of discriminating a defective product when the impedance ratio Z2 / Z1 is outside the above range. A method for producing a nonaqueous electrolyte secondary battery.

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