JP2010021043A - Separator, manufacturing method of separator and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator capable of maintaining characteristics for a long time even if charge and discharge are repeated by increasing liquid retention property of the separator, and capable of achieving high capacity of the high-rate discharge capacity, and a manufacturing method of the separator, and a battery. <P>SOLUTION: The separator 24 separates a positive electrode 21 and a negative electrode 22 and makes pass lithium ions while preventing short circuit of current due to contact of both the electrodes. Concretely, as the separator 24, for example, an insulating thin film having a large ion permeability and a prescribed mechanical strength is used. To be concrete, as the separator 24, one is used in which a porous film made of a polyolefin system material such as polypropylene or polyethylene is fibrillated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a separator, a separator manufacturing method, and a battery.

  2. Description of the Related Art In recent years, portable electronic devices such as notebook personal computers, camera-integrated VTRs (Videotape Recorders; video tape recorders), and mobile phones have appeared one after another, and their size and weight have been reduced. Along with this, secondary batteries have been spotlighted as portable power sources that are portable, and active research is being conducted to obtain higher energy density. Under such circumstances, lithium ion secondary batteries using non-aqueous electrolytes have been proposed as secondary batteries having higher energy density than aqueous electrolyte secondary batteries such as lead secondary batteries or nickel cadmium secondary batteries. Practical use has begun.

  Conventionally, in a lithium ion secondary battery, a liquid electrolyte (electrolytic solution) in which a lithium salt is dissolved in a nonaqueous solvent has been used as a substance that controls ion conduction. Therefore, in order to prevent liquid leakage, it is necessary to use a metal container as an exterior member and strictly ensure the airtightness inside the battery. However, when a metal container is used for the exterior member, it is extremely difficult to produce a thin and large area sheet type battery, a thin and small area card type battery or a flexible and flexible battery. there were.

  Therefore, a secondary battery using a gel electrolyte in which an electrolytic solution containing a lithium salt is held in a polymer material instead of the electrolytic solution has been proposed. (For example, refer to Patent Document 1) In this battery, since there is no problem of liquid leakage, a laminate film can be used for the exterior member, and the size, weight, and thickness can be reduced, and the degree of freedom in shape can be achieved. Can be realized.

JP 2001-266946 A

  However, in a secondary battery using a gel electrolyte, the liquid retention of the separator is lowered. In order to increase the capacity of the battery, a large amount of lithium ions that contribute to the reaction is required. Therefore, it is desirable that the separator has high liquid retention.

  Accordingly, an object of the present invention is to improve the liquid retention of the separator, maintain the characteristics for a long period of time even after repeated charge and discharge, and realize a high capacity discharge capacity separator and separator manufacturing method. And to provide a battery.

In order to solve the above-described problem, the first invention
A separator in which at least a part of the porous membrane is fibrillated.

The second invention comprises a positive electrode and a negative electrode, and a separator,
The separator is a battery in which at least a part of the porous membrane is fibrillated.
The separator is a battery whose surface is fibrillated.

3rd invention is a manufacturing method of the separator which has the process of raising at least one part of a porous membrane.

  In the first to third aspects of the invention, since at least a part of the porous membrane is fibrillated, the liquid retention of the separator can be improved, and long-term characteristics can be maintained even after repeated charge and discharge, and High capacity discharge capacity can be realized.

  According to the present invention, it is possible to improve the liquid retention of the separator, maintain the characteristics for a long period of time even when charging and discharging are repeated, and realize a high capacity discharge capacity at a high rate.

  Embodiments of the present invention will be described below with reference to the drawings. 1 shows an exploded view of a secondary battery according to an embodiment of the present invention, and FIG. 2 shows a cross-sectional structure taken along line II-II of the spirally wound electrode body 20 shown in FIG. It is. Here, a case of a secondary battery using lithium (Li) as an electrode reactive species will be described.

  This secondary battery has a configuration in which a flat wound electrode body 20 as a power generation element is sandwiched between exterior members 30a and 30b via adhesive layers 40a and 40b. The exterior members 30a and 30b are, for example, a metal laminate film obtained by laminating an insulating resin layer, a metal foil made of aluminum, and a heat fusion resin layer in this order, that is, an aluminum laminate film. The insulating resin layer is made of, for example, nylon, polyester, polyethylene terephthalate, or the like. The heat sealing resin layer is made of, for example, unstretched polypropylene (CPP) or polyethylene (PE).

  The adhesive layers 40a and 40b are for bonding the spirally wound electrode body 20 and the exterior members 30a and 30b, and have insulating properties. The adhesive layers 40a and 40b are, for example, double-sided pressure-sensitive adhesive tapes.

  The wound electrode body 20 has a configuration in which a positive electrode 21 and a negative electrode 22 are sequentially stacked via a separator 24 and wound. Although details will be described later, the separator 24 is made of a porous film such as a fibrillated microporous polyolefin film.

  A positive electrode tab 26 made of aluminum or the like is connected to the positive electrode 21, and a negative electrode tab 27 made of nickel or the like is connected to the negative electrode 22. For the connection between the positive electrode 21 and the positive electrode tab 26, for example, a manufacturing method that does not use another member for connection, such as ultrasonic welding or laser welding, is desirable. The connection between the negative electrode 22 and the negative electrode tab 27 is the same. For example, a manufacturing method that does not use another member for connection, such as ultrasonic welding or laser welding, is desirable. Further, the connection method between the positive electrode 21 and the positive electrode tab 26 and the connection method between the negative electrode 22 and the negative electrode tab 27 may be different.

  For example, an adhesion film 28 is inserted between the positive electrode tab 26 and the negative electrode tab 27 and the exterior members 30a and 30b, and the positive electrode tab 26 and the negative electrode tab 27 are led out from the exterior members 30a and 30b. The adhesion film 28 is for ensuring insulation and improving adhesion between the positive electrode tab 26 and the negative electrode tab 27 and the exterior members 30a and 30b.

  The positive electrode 21 has a structure in which, for example, a positive electrode mixture layer 21b is provided on both surfaces of a positive electrode current collector 21a. In addition, you may make it have the area | region in which the positive mix layer 21b was provided only in the single side | surface of the positive electrode collector 21a. The positive electrode current collector 21a has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The thickness of the positive electrode mixture layer 21b is, for example, 80 μm to 250 μm. This thickness is the total thickness when the positive electrode mixture layer 21b is provided on both surfaces of the positive electrode current collector 21a.

The positive electrode mixture layer 21b includes, for example, a positive electrode active material, and is configured with a conductive agent such as carbon black or graphite and a binder such as polyvinylidene fluoride as necessary. Examples of the positive electrode active material include metal oxides such as V ₂ O ₅ or lithium composite oxide, metal sulfides such as TiS ₂ or MoS _2, and polymer materials such as polyacetylene or polypyrrole. Any one of these or a mixture of two or more may be used.

Among these, a metal oxide is preferable because it has low reactivity with lithium and is difficult to form a lithium alloy. In particular, a lithium composite oxide is preferable because a voltage can be increased and an energy density can be increased. . Examples of the lithium composite oxide include those represented by the chemical formula Li _x MO ₂ . In the formula, M is preferably at least one of one or more transition metal elements, particularly cobalt (Co), nickel (Ni), and manganese (Mn). The value of x varies depending on the charge / discharge state of the battery, and is generally 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium composite oxide include LiCO ₂ , LiNi _y Co _1-y O ₂ (where 0 <y <1), LiMn ₂ O _{4 and the} like.

  The negative electrode 22 has, for example, a structure in which a negative electrode mixture layer 22b is provided on both surfaces of a negative electrode current collector 22a. In addition, you may make it have the area | region in which the negative mix layer 22b was provided only in the single side | surface of the negative electrode collector 22a. The negative electrode current collector 22a is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil having good electrochemical stability, electrical conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electrical conductivity. The thickness of the negative electrode current collector 22a is preferably about 6 μm to 40 μm, for example. If the thickness is less than 6 μm, the mechanical strength decreases, and the negative electrode current collector 22a is easily torn in the manufacturing process, resulting in a decrease in production efficiency. This is because the volume ratio becomes larger than necessary and it is difficult to increase the energy density. The thickness of the negative electrode mixture layer 22b is, for example, 80 μm to 250 μm. This thickness is the total thickness when the negative electrode mixture layer 22b is provided on both surfaces of the negative electrode current collector 22a.

  The negative electrode mixture layer 22b includes, for example, a negative electrode active material, and is configured with a binder such as polyvinylidene fluoride as necessary. The negative electrode active material preferably contains a negative electrode material capable of inserting and extracting lithium. In this specification, “occluding and releasing lithium” means that lithium ions are electrochemically inserted and released without losing their ionicity. This includes not only the case where lithium is present in a complete ionic state but also the case where it is present in a state that is not a complete ionic state. As a case corresponding to these, for example, occlusion by an electrochemical intercalation reaction of lithium ions with respect to graphite can be mentioned. In addition, occlusion of lithium into an alloy containing an intermetallic compound, or occlusion of lithium by forming an alloy can be given.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials, metal oxides, and polymer materials. Examples of the carbon material include pyrolytic carbons, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, spherical carbon, and activated carbon. Among these, cokes include pitch coke, needle coke, and petroleum coke. Organic polymer compound fired bodies are carbonized by firing polymer materials such as phenol resin and furan resin at an appropriate temperature. Carbon fibers include mesophase carbon fibers, and spherical carbon includes mesophase carbon microbeads. In addition, examples of the metal oxide include iron oxide, ruthenium oxide, and molybdenum oxide, and examples of the polymer material include polyacetylene and polypyrrole.

  Examples of the negative electrode material capable of absorbing and releasing lithium also include simple elements, alloys or compounds of metal elements or metalloid elements capable of forming an alloy with lithium. In addition to the alloy composed of two or more metal elements, the alloy includes an alloy composed of one or more metal elements and one or more metalloid elements. The structures include solid solutions, eutectics (eutectic mixtures), intermetallic compounds, or those in which two or more of them coexist.

Examples of such metal or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), Examples include gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr), and yttrium (Y). These alloys or compounds, for example, those represented by the chemical formula Ma _s Mb _t Li _u or a chemical formula Ma _p Mc _q Md _r,. In these chemical formulas, Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mb represents at least one of a metal element and a metalloid element other than lithium and Ma, Mc represents at least one of nonmetallic elements, and Md represents at least one of metallic elements and metalloid elements other than Ma. The values of s, t, u, p, q, and r are s> 0, t ≧ 0, u ≧ 0, p> 0, q> 0, and r ≧ 0, respectively.

  Among these, a simple substance, alloy or compound of a group 4B metal element or metalloid element is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.

Specific examples of such alloys or compounds include LiAl, AlSb, CuMgSb, 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, SiC, Si 3 N 4, Si 2 N 2 O, SiO V (0 < v ≦ 2), SnO _W (0 <w ≦ 2), SnSiO ₃ , LiSiO, or LiSnO.

  As a negative electrode material capable of inserting and extracting lithium, any one of these or a mixture of two or more thereof may be used.

  An electrolyte layer 23 made of a gel electrolyte is formed on the positive electrode mixture layer 21b and the negative electrode mixture layer 22b. The gel electrolyte is, for example, a polymer compound in which an electrolytic solution in which a lithium salt that is an electrolyte salt is dissolved in a solvent is held. Examples of the polymer compound include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polypropylene oxide, and polymethacrylonitrile, and any one or two or more of them are mixed depending on the usage form. May be used.

Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) _2, or LiN (C ₂ F ₅ SO ₂ ) ₂ , and any one of these or Two or more kinds may be mixed and used.

  The solvent dissolves and dissociates the electrolyte salt. As the solvent, for example, various non-aqueous solvents conventionally used can be used. Specifically, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, methyl propionate, dimethyl carbonate, Examples include diethyl carbonate, ethyl methyl carbonate, 2,4-difluoroanisole, 2,6-difluoroanisole, and 4-bromoveratrol, and any one of these or a mixture of two or more thereof may be used. .

  The separator 24 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator 24, for example, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used.

  Specifically, as the separator 24, a fibrillated porous film made of a polyolefin-based material such as polypropylene or polyethylene is used. Fibrilization means that the material constituting the separator is fluffed by rubbing with a paper file or the like. By fibrillation, the liquid retention of the electrolyte can be further improved. In order to obtain more excellent characteristics, it is preferable that both surfaces of the porous membrane are fibrillated, but only one surface may be fibrillated.

  The thickness of the separator 24 is preferably 1 μm or more and 20 μm or less as a thickness before fibrillation in consideration of mechanical strength and battery internal volume. The thickness when fibrillated is not limited to this, and the above-mentioned thickness is preferable as a material.

  The fibrillation method is not limited to the method of rubbing with a paper file, and various methods that can be fibrillated can be used.

The degree of fibrillation is more than 0.1% and preferably 30% or less, more preferably 5% or more and 30% or less, from the viewpoint that more excellent characteristics can be obtained. The degree of fibrillation indicates the ratio of the cross-sectional length that is fibrillated out of the total length of the cross section of the separator. That is, as shown in the schematic diagram of the separator 24 in FIG. 3, when the length of the entire cross section of the separator 24 is b, and the cross section length of the fibrillated portion is ba,
(formula)
The degree of fibrillation is obtained by “degree of fibrillation” = (“b−a” / b) × 100%.

  The method of measuring the degree of fibrillation is to immerse the entire separator 24 in a cured resin, dry the section for 24 hours, and then create a section by bending splitting, and observe the section with a scanning electron microscope (SEM). Can be measured. The sectioning by bending is not the sectioning by cutting with a cutter or the like, but the sectioning by breaking the resin as the entire resin is bent.

  As the electrolyte layer 23, a liquid electrolyte may be used, and the separator 24 may be impregnated with the liquid electrolyte. The liquid electrolyte includes, for example, a solvent and a lithium salt that is an electrolyte salt.

  For example, the secondary battery can be manufactured as follows. First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and then dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a positive electrode mixture slurry. After preparing the positive electrode mixture slurry, for example, the positive electrode mixture slurry is applied to both surfaces or one surface of the positive electrode current collector 21a made of a metal foil such as an aluminum (Al) foil, a nickel (Ni) foil, or a stainless steel foil and dried. The positive electrode mixture layer 21b is formed by compression molding to produce the positive electrode 21. At this time, the positive electrode mixture slurry is not applied to one end portion of the positive electrode current collector 21a, and the end portion is exposed.

  Next, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and then dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. After preparing the negative electrode mixture slurry, for example, the negative electrode mixture slurry is applied to both or one side of the negative electrode current collector 22a made of a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil, dried, and compressed. The negative electrode mixture layer 22b is formed to form the negative electrode 22. At this time, the negative electrode mixture is not applied to one end of the negative electrode current collector 22a, and the end is exposed.

  After producing the negative electrode 22, for example, the positive electrode tab 26 is attached to the exposed portion of the positive electrode current collector 21a, and the negative electrode tab 27 is attached to the exposed portion of the negative electrode current collector 22a, respectively, by resistance welding or ultrasonic welding. The positive electrode tab 26 and the negative electrode tab 27 can each be formed of a metal or alloy having electrical conductivity. For example, the positive electrode tab 26 is preferably formed of aluminum, and the negative electrode tab 27 is preferably formed of nickel.

  Next, for example, an electrolyte layer 23 made of a gel electrolyte is formed on the positive electrode mixture layer 21b and the negative electrode mixture layer 22b. After forming the electrolyte layer 23, for example, as shown in FIG. 2, the separator 24, the positive electrode 21 having the electrolyte layer 23 formed thereon, the separator 24, and the negative electrode 22 having the electrolyte layer 23 are sequentially stacked and wound. The wound electrode body 20 is formed by, for example, bonding a protective tape 25 to the portion.

  After forming the wound electrode body 20, for example, exterior members 30a and 30b made of an aluminum laminate film as shown in FIG. 1 are prepared and wound through the adhesive layers 40a and 40b as shown in FIG. The electrode body 20 is sandwiched between the exterior members 30a and 30b. Thereafter, in a reduced-pressure atmosphere, the exterior members 30a and 30b are pressure-bonded to the wound electrode body 20 by the adhesive layers 40a and 40b, and the outer edges of the exterior members 30a and 30b are heat-fused using the heat-fusion resin layer 33. Enclose it tightly by wearing. At that time, for example, an adhesion film 28 is inserted between the positive electrode tab 26 and the negative electrode tab 27 and the exterior members 30a and 30b, and the positive electrode tab 26 and the negative electrode tab 27 are led out from the exterior members 30a and 30b. This completes the assembly of the secondary battery. The shape of the secondary battery is not limited to the shape shown in FIGS. 1 and 2 and may be other shapes. After assembling the secondary battery, for example, the secondary battery is completed through a pressurization and aging process.

  According to one embodiment of the present invention, a separator in which the surface of a porous film made of a polyolefin resin or the like is fibrillated is used, so that long-term characteristics can be maintained even after repeated charging and discharging, and a high rate The discharge capacity can be increased.

  Further, specific examples of the present invention will be described. However, the present invention is not limited to these examples.

<Sample A>
First, 95% by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode material, 2% by mass of graphite as a conductive agent, and 3% by mass of polyvinylidene fluoride as a binder were prepared to prepare a positive electrode mixture. . Subsequently, N-methyl-2-pyrrolidone as a solvent was added to the positive electrode mixture, and the mixture was stirred and mixed with a homogenizer to obtain a positive electrode mixture slurry.

  Next, this positive electrode mixture slurry was uniformly applied to both surfaces of the positive electrode current collector 21a made of an aluminum foil and dried. After that, the positive electrode mixture layer 21b was formed by compression molding with a roller press, and cut into a predetermined size to produce a sheet-like positive electrode 21.

  Further, 90% by mass of artificial graphite as a negative electrode material and 10% by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Subsequently, N-methyl-2-pyrrolidone as a solvent was added to the negative electrode mixture, and the mixture was stirred and mixed with a homogenizer to obtain a negative electrode mixture slurry.

  Next, this negative electrode mixture slurry was uniformly applied to both surfaces of the negative electrode current collector 22a made of copper foil and dried. After that, the negative electrode mixture layer 22b was formed by compression molding with a roller press, and cut into a predetermined size to produce a sheet-like negative electrode 22.

Furthermore, LiPF ₆ was dissolved in a solvent in which ethylene carbonate and propylene carbonate were mixed to prepare an electrolytic solution. After that, this electrolytic solution, polyvinylidene fluoride as a polymer material, and dimethyl carbonate as a solvent for the polymer material were mixed and stirred to produce an electrolyte.

  After producing the positive electrode 21, the negative electrode 22 and the electrolyte, the positive electrode tab 26 is attached to the positive electrode current collector 21 a, the electrolyte is applied on the positive electrode mixture layer 21 b, dimethyl carbonate is volatilized, and the gel electrolyte layer 23 Formed. Moreover, while attaching the negative electrode tab 27 to the negative electrode collector 22a, the electrolyte was apply | coated on the negative mix layer 22b, dimethyl carbonate was volatilized, and the gel electrolyte layer 23 was formed. Subsequently, a separator 24 made of a microporous polyethylene film having a thickness of 16 μm was prepared, and the separator 24, the positive electrode 21, the separator 24, and the negative electrode 22 were laminated in this order, wound, and the protective tape 25 was adhered to form a flat shape. A wound electrode body 20 was obtained.

  After forming the wound electrode body 20, the exterior members 30a and 30b made of an aluminum laminate film are prepared, and the adhesion film 28 is disposed between the positive electrode tab 26 and the negative electrode tab 27 and the exterior members 30a and 30b, The revolving electrode body 20 was vacuum packaged, and a secondary battery was assembled. At this time, the adhesive layers 40 a and 40 b are interposed between the exterior members 30 a and 30 b and the wound electrode body 20.

<Sample B>
A battery of Sample B was produced in the same manner as Sample A, except that a separator having a fibrillation degree adjusted to 5% was used by rubbing both sides of a microporous polyethylene having a thickness of 16 μm with a paper file.

<Sample C>
A battery of Sample C was produced in the same manner as Sample A, except that a separator having a fibrillation degree adjusted to 10% was used by rubbing both sides of a microporous polyethylene having a thickness of 16 μm with a paper file.

<Sample D>
A battery of Sample D was prepared in the same manner as Sample A, except that a separator having a fibrillation degree adjusted to 30% was used by rubbing both sides of a microporous polyethylene having a thickness of 16 μm with a paper file.

<Sample E>
A battery of Sample E was prepared in the same manner as Sample A, except that a separator having a fibrillation degree adjusted to 50% was used by rubbing both sides of a microporous polyethylene having a thickness of 16 μm with a paper file.

<Sample α>
A battery of sample α was fabricated in the same manner as sample A, except that a separator made of a microporous polyethylene film having a thickness of 9 μm was used.

<Sample β>
A battery of sample β was produced in the same manner as sample α except that a separator having a fibrillation degree adjusted to 22% was used by rubbing both sides of a microporous polyethylene film having a thickness of 9 μm with a paper file. did.

<Sample γ>
A battery of sample γ is produced in the same manner as sample α except that a separator having a fibrillation degree adjusted to 40% is used by rubbing both sides of a microporous polyethylene film having a thickness of 9 μm with a paper file. did.

<Evaluation>
(Measurement of battery thickness)
The thickness of the battery was measured by sandwiching the cell between two plates placed in parallel and using a digimatic indicator so as not to vary depending on the measurement location.

(Measurement of battery capacity)
Obtain the discharge capacity as the battery capacity when charging with constant current and constant voltage at a constant voltage of 4.2V and 1C, and then discharging with constant current until the battery voltage reaches 3.0V with a constant current of 1C. It was.

(Measurement of energy density)
The energy density was determined by dividing the determined battery capacity by the battery volume.

  The measurement results are shown in Tables 1 and 2.

(Charge / discharge cycle characteristics)
In an environment of 23 ° C., constant current / constant voltage charging is performed with a charging voltage of 4.2V and 1C constant current, and then constant current discharging is performed until the battery voltage reaches 3.0V with a constant current of 1C. The discharge capacity at a certain number of cycles relative to the discharge capacity at the first cycle was determined as a discharge capacity retention ratio [(discharge capacity at a certain number of cycles / discharge capacity at the first cycle) × 100%].

  About the calculated | required result, the graph which plotted the discharge capacity maintenance factor with respect to the number of charging / discharging cycles was created and evaluated. FIG. 4 shows a graph plotting the discharge capacity retention ratio against the number of charge / discharge cycles.

(Discharge characteristics)
In an environment of 23 ° C., constant current and constant voltage charging is performed with a charging voltage of 4.2 V and a constant current of 1 C, and then 0.2 C (condition 1), 0.5 C (condition 2), and 1 C (condition 3) are constant. FIG. 5 shows the voltage transition when the constant current discharge is performed until the battery voltage reaches 3.0V by the current. In FIG. 5, the dotted line is the behavior of sample A, and the solid line is the behavior of sample D.

  As shown in Table 1, the battery capacity of Sample B to Sample E was larger than that of Sample A. Moreover, as shown in Table 2, the battery capacity of the samples β to γ was larger than that of the sample α. That is, it was found that the liquid retention can be improved and the capacity can be increased by fibrillation.

  As shown in Table 1, according to Sample B to Sample E, Sample E had a low energy density. As shown in Table 2, according to the samples α to γ, the energy density of the sample γ was small. That is, it was found that the degree of fibrillation is preferably 30% or less from the viewpoint of energy density.

  As shown in the graph of FIG. 4, the sample B to the sample E had better cycle characteristics than the sample A. That is, it was found that excellent cycle characteristics can be obtained by fibrillation.

  As shown in the graph of FIG. 5, it was found that the energy density is increased by fibrillation even when the discharge load is high.

  The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. In the above-described embodiments and examples, the non-aqueous electrolyte secondary battery having a winding structure has been described. However, the present invention is similarly applied to a battery having a structure in which a positive electrode and a negative electrode are folded or stacked. Can do. In addition, it can also be applied to so-called coin-type, button-type, and square-type batteries. Furthermore, it is not limited to a secondary battery, but can be applied to a primary battery. Further, for example, in the above-described embodiments and examples, the two exterior members 30a and 30b are bonded together to enclose the wound electrode body therein, but the outer edge portion is folded by folding one exterior member. May be sealed by another method such as sealing the wound electrode body.

1 is an exploded perspective view illustrating a secondary battery according to an embodiment of the present invention. It is sectional drawing along the II-II line of the winding electrode body shown in FIG. It is a schematic diagram of the separator used for the secondary battery by one embodiment of this invention. It is a graph which shows the measurement result of charging / discharging cycling characteristics. It is a graph which shows the measurement result of discharge characteristics.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Winding electrode body 21 ... Positive electrode 21a ... Positive electrode collector 21b ... Positive electrode mixture layer 22 ... Negative electrode 22a ... Negative electrode collector 22b ... Negative electrode mixture layer DESCRIPTION OF SYMBOLS 23 ... Electrolyte layer 24 ... Separator 25 ... Masking tape 26 ... Positive electrode tab 27 ... Negative electrode tab 28 ... Adhesion film 30a, 30b ... Exterior member 33 ... Thermal fusion Resin layer 40a, 40b ... Adhesive layer

Claims (9)

  A separator in which at least a part of a porous membrane is fibrillated. The separator according to claim 1, wherein the degree of fibrillation is in the range of more than 0.1% and 30% or less. The separator according to claim 1, wherein the degree of fibrillation is in the range of 5% to 30%. The separator according to claim 1, wherein both surfaces of the porous membrane are fibrillated. The separator according to claim 1, wherein the porous film is a porous film made of a polyolefin resin. A positive electrode and a negative electrode, and a separator;
The separator is a battery in which at least a part of a porous membrane is fibrillated. The battery according to claim 6, wherein the degree of fibrillation is in the range of more than 0.1% and 30% or less. The battery according to claim 6, which has a gel electrolyte as an electrolyte. A separator manufacturing method comprising a step of fluffing at least a part of a porous membrane.

Images