JP2012174412A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having enhanced safety and battery performance.SOLUTION: The nonaqueous electrolyte secondary battery 1 comprises: a positive electrode 3; a negative electrode 4; a separator 5 and a nonaqueous electrolyte. The separator 5 comprises one or more first nonwoven fabric layers 9 containing fibers having an average diameter R1 and one or more second nonwoven fabric layers 10 containing fibers having an average diameter R2. One or more first nonwoven fabric layers 9 and one or more second nonwoven fabric layers 10 are alternately stacked so that a direction of the fibers in the first nonwoven fabric layer 9 and a direction of the fibers in the second nonwoven fabric layer 10 have an angle. The R1 and the R2 have a different value.

Description

  Embodiments described herein relate generally to a non-aqueous electrolyte secondary battery.

  In recent years, lithium-ion batteries having high energy density have been widely used as power sources for small portable electronic devices such as mobile phones and notebook personal computers. An electrode of a lithium ion battery generally has a configuration in which a positive electrode and a negative electrode are stacked via a separator. In order to further increase the capacity of the lithium ion battery, it is desirable that the separator is thinner. However, if the separator is made too thin, the strength is reduced and an internal short circuit may occur. Further, for example, a separator manufactured by stretching a sheet made of a polyolefin resin at a high magnification may remarkably shrink under a high temperature environment such as an abnormal temperature rise due to an internal short circuit, and may not function as a partition between electrodes.

Japanese Patent Application Laid-Open No. 09-012756 Japanese Patent Laid-Open No. 05-310989

  The problem to be solved by the present invention is to provide a non-aqueous electrolyte secondary battery with improved safety and battery performance.

  The nonaqueous electrolyte secondary battery of the embodiment includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The separator includes one or more first nonwoven layers including fibers having an average diameter R1 and one or more second nonwoven layers including fibers having an average diameter R2. The one or more first nonwoven fabric layers and the one or more second nonwoven fabric layers are alternately arranged, and the direction of the fibers of the first nonwoven fabric layer and the direction of the fibers of the second nonwoven fabric layer are at an angle. Laminated to have. R1 is different from R2.

The partial notch perspective view of the nonaqueous electrolyte secondary battery of 1st Embodiment. The schematic diagram which shows the electrode group with which the battery of FIG. 1 is equipped. The schematic diagram which shows the side surface of the separator used for the battery of 1st Embodiment. The schematic diagram which shows the side surface of the separator used for the battery of 2nd Embodiment. The schematic diagram which shows the side surface of the separator used for the battery of 3rd Embodiment. The schematic diagram which shows the side surface of the separator used for the battery of 4th Embodiment. The graph which shows the change of the amount of heat dissipation. The graph which shows the change of cell temperature. The graph which shows discharge time. The graph which shows the relationship between the number of layers of a separator, and volume energy density.

  Hereinafter, a nonaqueous electrolyte secondary battery according to an embodiment will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 is a partially cutaway perspective view of a thin nonaqueous electrolyte secondary battery 1. FIG. 2 is a schematic diagram in which the wound electrode group 2 provided in the battery of FIG. 1 is developed.

  The nonaqueous electrolyte secondary battery 1 according to the present embodiment includes a wound electrode group 2. The wound electrode group 2 includes a positive electrode 3, a negative electrode 4, and a separator 5. The positive electrode 3 and the negative electrode 4 are stacked with a separator 5 interposed therebetween. The wound electrode group 2 is formed by winding the laminated body into a flat shape. A strip-like positive electrode tab 6 is electrically connected to the positive electrode 3. A strip-shaped negative electrode tab 7 is electrically connected to the negative electrode 4.

  The wound electrode group 2 is accommodated in the exterior member 8 with the end portions of the positive electrode tab 6 and the negative electrode tab 7 extended to the outside. Further, a non-aqueous electrolyte (not shown) is accommodated in the exterior member 8. As the exterior member 8, a laminate film exterior bag is used. The electrode group 2 and the non-aqueous electrolyte are sealed by heat-sealing the opening of the laminate film outer packaging bag with the positive electrode tab 6 and the negative electrode tab 7 extending. The exterior member is not limited to a laminate film, and for example, a metal can can be used.

  Hereinafter, the separator, the positive electrode, the negative electrode, the nonaqueous electrolyte, and the exterior member will be described in detail.

1) Separator The separator is disposed between the positive electrode and the negative electrode, and prevents the positive electrode and the negative electrode from contacting each other. The separator is made of an insulating material. The separator has a shape in which the electrolyte can move between the positive electrode and the negative electrode.

  A separator 5 used in the nonaqueous electrolyte secondary battery 1 according to the present embodiment is shown in FIG. FIG. 3 is a side view of the separator 5 and is a schematic view of the separator 5 viewed from the thickness direction. The separator 5 includes one or more first nonwoven layers 9 including fibers having an average diameter R1, and one or more second nonwoven layers 10 including fibers having an average diameter R2. The one or more first nonwoven fabric layers 9 and the one or more second nonwoven fabric layers 10 are alternately arranged, and the direction of the fibers of the first nonwoven fabric layer 9 and the direction of the fibers of the second nonwoven fabric layer 10 are at an angle. The stacked structure is formed by stacking the layers so as to include the stacked structure. Furthermore, R1 is a value different from R2.

  For the first nonwoven fabric layer 9, a nonwoven fabric composed of fibers having an average diameter R1 is used. For the second nonwoven fabric layer 10, a nonwoven fabric composed of fibers having an average diameter R2 is used. The average diameter of the fibers constituting the nonwoven fabric can be measured by, for example, a scanning electron microscope (SEM).

  The first nonwoven fabric layer 9 is laminated so that the direction of the fibers has an angle with the direction of the fibers of the second nonwoven fabric layer 10. That is, in a laminated structure, each nonwoven fabric layer is arrange | positioned so that an adjacent nonwoven fabric layer and the direction of a fiber may not become parallel.

  In the example of FIG. 3, the first nonwoven fabric layer 9 is arranged in a direction in which the fiber diameter direction can be seen, while the second nonwoven fabric layer 10 is arranged in a direction in which the fiber length direction of the fiber can be seen. Therefore, the 1st nonwoven fabric layer 9 and the 2nd nonwoven fabric layer 10 are laminated | stacked so that those fiber directions may be substantially orthogonal.

  Here, the direction of the fibers contained in the nonwoven fabric layer is understood to mean the fiber length direction of the fibers contained in the nonwoven fabric layer. Although all the fibers may be arrange | positioned toward the same direction as the fiber contained in a nonwoven fabric layer, it is more preferable that it arrange | positions disorderly. When the fibers are arranged in a disorderly manner, the main direction of the first nonwoven fabric region serving as the base is defined as the direction of the fibers contained in the nonwoven fabric layer.

  As shown in FIG. 3, the first nonwoven fabric layer 9 and the second nonwoven fabric layer 10 are not limited to being laminated so that the directions of the fibers are substantially orthogonal, but the directions of the fibers are substantially parallel. As long as it is not, the angle may be arbitrary. The acute angle formed by the fiber direction of the first nonwoven fabric layer 9 and the fiber direction of the second nonwoven fabric layer 10 is preferably 10 ° or more, for example.

  Furthermore, the 1st nonwoven fabric layer 9 and the 2nd nonwoven fabric layer 10 are formed with the fiber from which thickness differs. That is, the average diameter R1 of the fibers contained in the first nonwoven fabric layer 9 and the average diameter R2 of the fibers contained in the second nonwoven fabric layer 10 are different values.

  Although the average diameter R1 of the fiber contained in the 1st nonwoven fabric layer 9 is not specifically limited, For example, it is preferable that it is the range of 5-10 micrometers. Although the average diameter R2 of the fiber contained in the 2nd nonwoven fabric layer 10 is not specifically limited, For example, it is preferable that it is the range of 1-5 micrometers.

  The length of the fiber contained in the 1st nonwoven fabric layer 9 and the 2nd nonwoven fabric layer 10 is not specifically limited, Arbitrary length may be sufficient.

  In the separator as described above, the nonwoven fabric layers having different fiber diameters are laminated so that the fiber directions are not parallel to each other. Have Since such a separator has high lithium ion permeability, it can improve the charge / discharge rate, and since it has high strength, it can prevent short circuits and improve battery safety. Furthermore, since the strength of the separator is high, the thickness of the separator can be further reduced, which can contribute to an increase in battery capacity. Furthermore, since the separator is composed of a plurality of members and is structurally discontinuous, it has an advantage that the shrinkage rate is lower than that of a separator composed of a single member, and shrinkage at an abnormally high temperature is reduced. .

  Examples of the material of the separator include synthetic resin and cellulose. For example, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or a cellulose-based separator can be used. In particular, a separator formed from cellulose is difficult to shrink even under an abnormally high temperature due to overcharge or internal short circuit.

  The thickness of the separator is preferably 1 to 20 μm, and more preferably 1 to 10 μm. By setting the thickness within the above range, the lithium ion has sufficient strength and the lithium ion permeability can be improved.

  The nonwoven fabric contained in the separator 5 used in the present embodiment can be manufactured by a known method such as a dry method, a spunbond method, a water needle method, a spunlace method, a wet papermaking method, and a melt blow method. . In particular, a wet papermaking method that facilitates obtaining a uniform and thin nonwoven fabric is preferably used. The nonwoven fabric is preferably a porous film made of an organic polymer that swells in and retains the electrolyte solution, and has an average film thickness of 10 to 20 μm, a basis weight of 6 to 20 g / m 2, an air permeability of 10 seconds or less, and at 25 ° C. The Macmillan number is desirably 10 or less.

  The material constituting the non-woven fabric is not particularly limited, but is selected from a polyolefin material such as polyethylene and polypropylene, a polyester material such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulfide, aromatic polyamide, and a mixture thereof. can do.

  In addition, although the example which laminates | stacks two types of nonwoven fabric layers of a 1st nonwoven fabric layer and a 2nd nonwoven fabric layer alternately, and formed a laminated structure in the above was not limited to this, but 3 or more types were included. A laminated structure may be formed by alternately laminating nonwoven fabric layers. In this case, it is preferable that the three or more kinds of nonwoven fabrics are formed from fibers having different average diameters. Further, the three or more kinds of nonwoven fabric layers are arranged such that the directions of the fibers are not parallel to the directions of the fibers of the adjacent nonwoven fabric layers.

  Further, the total number of nonwoven fabric layers included in the separator is not limited to four layers, and five or more nonwoven fabric layers may be included.

  Further, the separator may be impregnated with a thermoplastic resin. The thermoplastic resin melts when the battery reaches an abnormally high temperature due to overcharge or internal short circuit. When the thermoplastic resin melts, the gaps in the separator are closed, and the permeation of lithium ions is restricted. Therefore, by including a thermoplastic resin in the separator, the current can be interrupted in an abnormally high temperature state.

  As the thermoplastic resin, polypropylene (PP) resin, polyethylene (PE) resin, fluororesin, silicon resin, acrylic resin, or the like can be used. PP resin and PE resin are preferably used. These thermoplastic resins may be used alone or as a mixture of a plurality of types.

2) Positive electrode The positive electrode includes a current collector and a positive electrode layer. The positive electrode layer is formed on one side or both sides of the current collector. The positive electrode layer includes a positive electrode active material, a conductive agent, and a binder.

Examples of the positive electrode active material include lithium manganese composite oxide (for example, LiMn ₂ O ₄ or LiMnO ₂ ), lithium nickel composite oxide (for example, LiNiO ₂ ), lithium cobalt composite oxide (LiCoO ₂ ), and lithium nickel cobalt composite oxide. (Eg, LiNi _1-x Co _x O ₂ , 0 <x ≦ 1), lithium manganese cobalt composite oxide (eg, LiMn _x Co _1-x O _2, 0 <x ≦ 1), lithium iron phosphate (LiFePO ₄ ), And lithium composite phosphate compounds (for example, LiMn _x Fe _1-x PO _4, 0 <x ≦ 1).

  Examples of the conductive agent include acetylene black, carbon black, and graphite.

  Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, ethylene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and carboxymethylcellulose (CMC). ) Is included.

  The mixing ratio of the active material, the conductive agent, and the binder is preferably, for example, 80 to 95% by weight of the active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

As an example, 91% by weight of lithium cobalt oxide (LiCoO ₂ ) powder as a positive electrode active material, 2.5% by weight of acetylene black and 3% by weight of graphite as a conductive agent, and 3.5% by weight of polyvinylidene fluoride (PVdF) as a binder % Is added to a normal methylpyrrolidone (NMP) solution and mixed to prepare a slurry. The slurry is applied to a current collector made of an aluminum foil having a thickness of 15 μm, dried, and then pressed to produce a positive electrode. be able to. At this time, the electrode density can be adjusted by adjusting the press pressure, for example, 3.0 g / cm ³ .

3) Negative electrode The negative electrode includes a current collector and a negative electrode layer. The negative electrode layer is formed on one side or both sides of the current collector. The negative electrode layer includes a negative electrode active material, a conductive agent, and a binder.

  As the negative electrode active material, a material capable of occluding and releasing lithium ions is used. Examples of the negative electrode active material include carbon materials, metal oxides, metal sulfides, metal nitrides, and metal alloys.

  Examples of the carbon material include coke, carbon fiber, pyrolytic gas phase carbide, graphite, and resin fired body.

Examples of the metal oxide include lithium titanate (Li _{4 + x} Ti ₅ O ₁₂ ).
Examples of metal sulfides include iron sulfide and lithium sulfide.
Examples of the metal nitride include lithium cobalt nitride.
Examples of metal alloys include aluminum and aluminum alloys, lithium and lithium alloys.
As the negative electrode active material, the above substances may be used alone, or two or more kinds may be mixed and used.

  A carbon material can be used for the conductive agent contained in the negative electrode layer. Examples of the carbon material include acetylene black and carbon black.

  Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), polypropylene (PP), polyethylene (PE), and carboxymethyl cellulose (CMC). ) Is included.

  The blending ratio of the active material, the conductive agent and the binder is preferably, for example, 70 to 95% by weight of the negative electrode active material, 0 to 25% by weight of the conductive agent, and 2 to 10% by weight of the binder.

As an example, 91% by weight of lithium titanate powder as a negative electrode active material, 3.5% by weight of acetylene black and 3% by weight of graphite as a conductive agent, 2.5% by weight of polyvinylidene fluoride (PVdF) as a binder, A slurry can be prepared by adding to and mixed with a pyrrolidone (NMP) solution. The slurry is applied to a current collector made of an aluminum foil having a thickness of 15 μm, dried, and then pressed to produce a negative electrode. At this time, the electrode density can be adjusted by adjusting the press pressure, for example, 1.3 g / cm ³ .

4) Non-aqueous electrolyte The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.
As the non-aqueous solvent, a non-aqueous solvent known to be used for lithium batteries can be used. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC); chain carbonates such as dimethyl carbonate, methyl ethyl carbonate or diethyl carbonate; γ-butyrolactone, acetonitrile, methyl propionate , Ethyl propionate; cyclic ethers such as tetrahydrofuran or 2-methyltetrahydrofuran; chain ethers such as dimethoxyethane or diethoxyethane.

As the electrolyte, an alkali salt can be used. Preferably lithium salt is used. Examples of lithium salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), and trifluoro Lithium metasulfonate (LiCF ₃ SO ₃ ) is included. In particular, lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) are preferably used. The concentration of the electrolyte in the non-aqueous solvent is preferably 0.5 to 2 mol / L, for example.

5) Exterior member As the exterior member, a laminate film or a metallic container can be used.

  A multilayer film made of a metal layer coated with a resin layer is used as the laminate film. As the resin forming the resin layer, polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET) can be used. The metal layer is preferably an aluminum foil or an aluminum alloy in order to reduce the weight of the battery.

  The exterior member made of a laminate film can be formed by forming the inner surface with a thermoplastic resin such as PP and PE, and performing sealing by, for example, a heat sealing method. The thickness of the laminate film is preferably 0.2 mm or less in order to improve the volume energy density.

  As the metal container, for example, a container formed of aluminum or an aluminum alloy can be used. The aluminum alloy is preferably an alloy containing an element selected from magnesium, zinc and silicon. When the aluminum alloy contains a transition metal such as iron, copper, nickel and chromium, it is preferably 100 ppm or less.

  The shape of the container may be, for example, a square shape, a coin shape, or a button shape. The container preferably has a wall thickness of 0.5 mm or less.

  According to the present embodiment, a non-aqueous electrolyte secondary battery with high safety and improved battery performance can be provided by using a separator having high lithium ion permeability and high strength.

(Second Embodiment)
Next, the nonaqueous electrolyte secondary battery according to the second embodiment will be described. FIG. 4 is a side view of the separator 11 used in the battery of the second embodiment, and is a schematic view of the long side of the separator 11 as viewed from the thickness direction. The nonaqueous electrolyte secondary battery according to the second embodiment has the same configuration as that of the first embodiment except that a separator having a configuration as shown in FIG. 4 is used.

  The separator 11 includes one or more first nonwoven layers 9 including fibers having an average diameter R1, and one or more second nonwoven layers 10 including fibers having an average diameter R2. The one or more first nonwoven fabric layers 9 and the one or more second nonwoven fabric layers 10 are alternately arranged, and the direction of the fibers of the first nonwoven fabric layer 9 and the direction of the fibers of the second nonwoven fabric layer 10 are at an angle. The stacked structure is formed by stacking the layers so as to include the stacked structure.

  Here, the diameter and length of the fibers forming each nonwoven fabric layer, the fiber direction, the angle formed by the fiber direction of the adjacent nonwoven fabric layer, and the like are as described in the first embodiment.

  In addition to a laminated structure in which one or more first nonwoven fabric layers and one or more second nonwoven fabric layers are alternately laminated, the separator used in this embodiment further penetrates the laminated structure in the thickness direction. A support 12 is included. The support 12 can be used as a skeleton of the separator 11. By using the support 12, the strength of the separator 11 can be further improved.

  The support 12 has, for example, a columnar shape having the same thickness as the laminated structure in which the first nonwoven fabric layers and the second nonwoven fabric layers are alternately laminated, and having the same length as the length in the short side direction of the separator 11. It may be a shape. Such supports 12 can be arranged in the separator 11 at equal intervals in parallel with the short side direction.

  The support 12 is preferably a porous body that is permeable to lithium ions. For example, a nonwoven fabric formed from a resin such as polyolefin and polyethylene can be used.

  However, since the support 12 formed from these resins has lower lithium ion permeability than the laminated structure formed by the first and second nonwoven fabric layers, the width of the support 12, that is, the separator 11. When the length in the same direction as the long side direction is too large, the lithium ion permeability of the separator is lowered. Therefore, the width of the support 12 needs to be adjusted appropriately. For example, as shown in FIG. 4, it is preferable that the area occupied by the support 12 per cross-sectional area of the separator 11 is adjusted to be 50% or less. If the area of the support 12 is 50% or less, the strength of the separator 11 can be improved without impairing lithium ion permeability. In addition, the area which the support body 12 occupies is, for example, within a certain field of view of the cross-sectional area of the separator 11, the support body with respect to the total area of the laminated structure formed by the first and second nonwoven fabric layers and the support body. It can be a ratio of the area.

  As another example, the support has, for example, the same thickness as the laminated structure in which the first nonwoven fabric layer and the second nonwoven fabric layer are alternately laminated, and the length in the long side direction of the separator. It may be a columnar shape having the same length. Such supports can be arranged in the separator at equal intervals in parallel with the long side direction. The support may be arranged in a lattice shape or a mesh shape.

  In the separator 11 used in the present embodiment, for example, supports are arranged at equal intervals, and one nonwoven fabric layer and a second nonwoven fabric layer are alternately laminated between the supports in the same manner as in the first embodiment. Can be manufactured.

  According to the second embodiment, it is possible to provide a non-aqueous electrolyte secondary battery with high safety and improved battery performance by using a separator having high lithium ion permeability and high strength.

(Third embodiment)
Next, the nonaqueous electrolyte secondary battery according to the third embodiment will be described. FIG. 5 is a side view of the separator 13 used in the battery of the third embodiment, and is a schematic view of the separator 13 as viewed from the thickness direction. The nonaqueous electrolyte secondary battery according to the third embodiment has the same configuration as that of the first embodiment except that a separator having a configuration as shown in FIG. 5 is used.

  The separator 13 includes one or more first nonwoven fabric layers 9 including fibers having an average diameter R1 and one or more second nonwoven fabric layers 10 including fibers having an average diameter R2. The one or more first nonwoven fabric layers 9 and the one or more second nonwoven fabric layers 10 are alternately arranged, and the direction of the fibers of the first nonwoven fabric layer 9 and the direction of the fibers of the second nonwoven fabric layer 10 are at an angle. The stacked structure is formed by stacking the layers so as to include the stacked structure.

  In this embodiment, this laminated structure is characterized in that the opposing surfaces of the adjacent first nonwoven fabric layer and second nonwoven fabric layer are fused. Here, the surface of the nonwoven fabric layer being fused means that adjacent layers are mixed in the vicinity of the contact surface, and the boundary between the adjacent nonwoven fabric layers is not clearly separated. As shown in FIG. 5, the adjacent first nonwoven fabric layer 9 and second nonwoven fabric layer 10 are mixed in the second nonwoven fabric layer 10 with fibers forming the first nonwoven fabric layer 9 in the vicinity of the contact surface. On the contrary, the fibers forming the second nonwoven fabric layer 10 are in a state of being mixed in the first nonwoven fabric layer 9.

  According to this embodiment, the separator in which the surface of the adjacent first nonwoven fabric layer and the surface of the second nonwoven fabric layer are fused has the advantage that the overall thickness is reduced. When the thickness is reduced, the distance between the positive and negative electrodes is shortened, so that lithium ion permeability can be improved. Further, when the thickness is reduced, the energy density of the battery can be increased.

  In addition, the diameter of fiber which forms each nonwoven fabric layer, length, the direction of a fiber, etc. are as having described in 1st Embodiment.

  The nonwoven fabric contained in the separator 13 used in the present embodiment can be manufactured by a known method such as a dry method, a spunbond method, a water needle method, a spunlace method, a wet papermaking method, and a melt blow method. . In particular, a wet papermaking method that facilitates obtaining a uniform and thin nonwoven fabric is preferably used. The nonwoven fabric is preferably a porous film made of an organic polymer that swells in and retains the electrolyte solution, and has an average film thickness of 10 to 20 μm, a basis weight of 6 to 20 g / m 2, an air permeability of 10 seconds or less, and at 25 ° C. The Macmillan number is desirably 10 or less.

  The material constituting the non-woven fabric is not particularly limited, but is selected from a polyolefin material such as polyethylene and polypropylene, a polyester material such as polyethylene terephthalate and polybutylene terephthalate, polyphenylene sulfide, aromatic polyamide, and a mixture thereof. can do.

  According to the third embodiment, a non-aqueous electrolyte secondary battery with high safety and improved battery performance can be provided by using a separator having high lithium ion permeability and high strength.

(Fourth embodiment)
Next, the nonaqueous electrolyte secondary battery according to the fourth embodiment will be described. FIG. 6 is a side view of the separator 14 used in the battery of the fourth embodiment, and is a schematic view of the long side of the separator 14 as seen from the thickness direction. The nonaqueous electrolyte secondary battery according to the fourth embodiment has the same configuration as that of the first embodiment except that a separator having a configuration as shown in FIG. 6 is used.

  The separator 14 includes one or more first nonwoven layers 9 including fibers having an average diameter R1 and one or more second nonwoven layers 10 including fibers having an average diameter R2. The one or more first nonwoven fabric layers 9 and the one or more second nonwoven fabric layers 10 are alternately arranged, and the direction of the fibers of the first nonwoven fabric layer 9 and the direction of the fibers of the second nonwoven fabric layer 10 are at an angle. The stacked structure is formed by stacking the layers so as to include the stacked structure.

  In addition to the laminated structure, the separator further includes a support 12 that penetrates the laminated structure in the thickness direction. This support 12 has the same thickness as a laminated structure in which the first nonwoven fabric layer 9 and the second nonwoven fabric layer 10 are laminated, and can be used as a skeleton of the separator 11. By using the support 12, the strength of the separator 11 can be further improved.

  Here, the diameter and length of the fibers forming each nonwoven fabric layer, the fiber direction, the angle formed by the fiber directions of the adjacent nonwoven fabric layers, the shape and arrangement of the support, and the like are as described in the second embodiment. .

  As shown in FIG. 6, in this embodiment, a further nonwoven fabric layer is further laminated outside the laminated structure. In the example of FIG. 6, a third nonwoven fabric layer 15 is laminated outside the first nonwoven fabric layer 9, and a fourth nonwoven fabric layer 16 is laminated outside the second nonwoven fabric layer 10.

  It is preferable that the 3rd nonwoven fabric layer 15 and the 4th nonwoven fabric layer 16 differ in the average diameter of the fiber contained from the average diameter of the fiber contained in an adjacent nonwoven fabric layer. Moreover, it is preferable that the 3rd nonwoven fabric layer 15 and the 4th nonwoven fabric layer 16 are each laminated | stacked so that the direction of the fiber may have an angle with the direction of the fiber of an adjacent nonwoven fabric layer.

  By laminating a further non-woven fabric layer on at least one outer side of the laminated structure as described above, the strength of the separator can be further improved. Even when there is a step between the first nonwoven fabric layer or the second nonwoven fabric layer and the support 12, the surface of the separator 14 can be smoothed.

  The separator 14 used in this embodiment can be manufactured by further laminating a nonwoven fabric layer on one surface or both surfaces of the separator produced by the method described in the second embodiment.

  According to the fourth embodiment, a non-aqueous electrolyte secondary battery with high safety and improved battery performance can be provided by using a separator having high lithium ion permeability and high strength.

  The non-aqueous electrolyte secondary battery according to each of the above embodiments may be provided as a vehicle battery mounted on a two-wheeled or four-wheeled vehicle, in addition to a small battery mounted on a portable electronic device or the like. it can. In addition, the nonaqueous electrolyte secondary battery according to each of the above embodiments is not limited to a thin shape, and may be in any form such as a cylindrical shape or a rectangular shape. Further, the electrode group provided in the nonaqueous electrolyte secondary battery is not limited to the wound electrode group, and may be a stacked electrode group.

(Example)
<Preparation of separator>
Polyethylene films having a thickness of 15 μm were arranged at intervals of about 20 μm to form a separator skeleton. A separator was prepared by sequentially laminating a first nonwoven fabric layer and a second nonwoven fabric layer between polyethylene films. As the fibers contained in the first nonwoven fabric layer, cellulose fibers having an average diameter of 5 μm were used. As the fibers contained in the second nonwoven fabric layer, cellulose fibers having an average diameter of 2 μm were used. The first non-woven fabric layer and the second non-woven fabric layer were laminated so that the directions of the fibers were substantially perpendicular. The first nonwoven fabric layer had a thickness of 5 μm per layer, and the second nonwoven fabric layer had a thickness of 2 μm per layer, and two layers were laminated.

<Preparation of positive electrode>
As a positive electrode active material, 91% by weight of lithium cobalt oxide (LiCoO ₂ ) powder, 2.5% by weight of acetylene black, 3% by weight of graphite, and 3.5% by weight of polyvinylidene fluoride (PVdF) were mixed with normal methylpyrrolidone (NMP). ) Added to the solution and mixed to prepare a paste-like positive electrode slurry. The slurry was passed through a 70 mesh screen to remove the large ones. Subsequently, it apply | coated uniformly on both surfaces of the strip-shaped aluminum foil of thickness 12 micrometers, and dried. Next, after press forming and cutting to a predetermined size, the conductive tab was welded.

<Production of negative electrode>
As a negative electrode active material, 91% by weight of lithium titanate powder, 3.5% by weight of acetylene black, 3% by weight of graphite, and 2.5% by weight of polyvinylidene fluoride (PVdF) were added to a normal methylpyrrolidone (NMP) solution. The mixture was mixed to prepare a paste-like negative electrode slurry. The slurry was passed through a 70 mesh screen to remove the large ones. Subsequently, it apply | coated uniformly on both surfaces of the strip-shaped aluminum foil of thickness 12 micrometers, and dried. Next, after press forming and cutting to a predetermined size, the conductive tab was welded.

<Preparation of nonaqueous electrolyte secondary battery>
The positive electrode, separator, and negative electrode prepared above were stacked in this order, wound, and press-molded to prepare a wound electrode group.

LiPF ₆ was dissolved at a concentration of 1 mol / dm ³ in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 2 to prepare a nonaqueous electrolyte.

  Put the wound electrode group and the non-aqueous electrolyte in the laminated film outer bag, heat seal with the positive electrode tab and the negative electrode tab extended, and seal the wound electrode group and the non-aqueous electrolyte solution. A secondary battery was produced.

(Comparative Example 1)
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a separator having a single layer structure was used. The separator was formed from cellulose fibers having an average diameter of 10 μm and had a thickness of 15 μm.

(Comparative experiment)
After charging the batteries of Examples and Comparative Examples, the performance when discharging was tested. The charge / discharge conditions were all 1C.

  FIG. 7 shows the measurement result of the amount of heat dissipated. As shown in FIG. 7, it was shown that the battery of the example had a larger amount of heat dissipated and higher heat dissipation capability than the battery of the comparative example.

  FIG. 8 shows the measurement result of the cell temperature. As shown in FIG. 8, it was shown that the battery of the example had a slower start of cell temperature rise than the battery of the comparative example, and the temperature rise was suppressed.

  FIG. 9 shows the measurement results of the discharge time. As shown in FIG. 9, the battery of the example had a higher voltage and a longer discharge time than the battery of the comparative example.

(Relationship between number of separator layers and volume energy density)
The relationship between the number of separator layers and the volume energy density is shown in FIG. In the battery of the comparative example, the volume energy density significantly decreases as the number of separator layers increases. However, when the separator according to the present embodiment was used, the decrease in volume energy density was gradual. The separator according to this embodiment has been shown to be advantageous for improving the volume energy density.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Non-aqueous electrolyte secondary battery, 2 ... Winding electrode group, 3 ... Positive electrode, 4 ... Negative electrode, 5, 11, 13, 14 ... Separator, 6 ... Positive electrode tab, 7 ... Negative electrode tab, 8 ... Exterior member, 9 ... 1st nonwoven fabric layer, 10 ... 2nd nonwoven fabric layer, 12 ... Support body, 15 ... 3rd nonwoven fabric layer, 16 ... 4th nonwoven fabric layer.

Claims (6)

A positive electrode;
A negative electrode,
A separator comprising one or more first nonwoven layers comprising fibers having an average diameter R1, and one or more second nonwoven layers comprising fibers having an average diameter R2.
Including non-aqueous electrolyte,
The one or more first nonwoven fabric layers and the one or more second nonwoven fabric layers are alternately arranged, and the direction of the fibers of the first nonwoven fabric layer and the direction of the fibers of the second nonwoven fabric layer are at an angle. Laminated to have
The non-aqueous electrolyte secondary battery, wherein R1 has a value different from R2.   The separator further includes a support that penetrates in a thickness direction a laminated structure in which the one or more first nonwoven fabric layers and the one or more second nonwoven fabric layers are alternately laminated. Item 2. The nonaqueous electrolyte secondary battery according to Item 1.   3. The nonaqueous electrolyte secondary battery according to claim 2, wherein in the laminated structure, opposing surfaces of the adjacent first nonwoven fabric layer and the second nonwoven fabric layer are fused.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the support is a porous body.   The nonaqueous electrolyte secondary battery according to any one of claims 2 to 4, wherein a further nonwoven fabric layer is laminated outside the laminated structure. The further nonwoven layer is laminated such that the fiber direction has an angle with the fiber direction of the adjacent nonwoven layer;
6. The nonaqueous electrolyte secondary battery according to claim 5, wherein an average diameter of fibers contained in the further nonwoven fabric layer is a value different from an average diameter of fibers contained in an adjacent nonwoven fabric layer.

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