JP5203632B2 - Non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte battery.

  Nonaqueous electrolyte batteries that include a nonaqueous electrolyte and are charged and discharged via lithium ions have characteristics such as high energy density and are widely used in small portable devices typified by mobile phones and the like. In recent years, non-aqueous electrolyte batteries for electric vehicles, hybrid vehicles, power storage, etc. due to the demand for rapid charging / discharging for the purpose of miniaturization and improvement of convenience of portable devices and the increasing interest in environmental issues. There are increasing demands for improving energy density, input / output characteristics, and cycle characteristics.

  In a nonaqueous electrolyte battery, methods for improving energy density, rapid charge / discharge characteristics, and input / output characteristics include increasing the specific surface area of the active material, increasing the foil thickness of the electrode, and increasing the density.

  On the other hand, as described in Patent Document 1, a negative electrode current collector made of aluminum or an aluminum alloy foil and a negative electrode active material having a fine particle size distribution such that the primary particle diameter is 1 μm or less are included. Nonaqueous electrolyte batteries have been proposed. According to this, since a powder having a fine particle size distribution can be used as the negative electrode active material, energy density and input / output characteristics can be improved.

  Taking advantage of the characteristics of the battery described in Patent Document 1, development of a battery having an electrode group structure that is larger and that can obtain a large output in consideration of application to non-aqueous electrolyte batteries for electric vehicles, hybrid vehicles, power storage, etc. Is desired. Patent Document 1 describes an example of a battery having a thickness of 3.8 mm, a width of 63 mm, and a height of 95 mm. In order to manufacture a battery larger than this, it is necessary to lower the electrical resistance of the current collector that conducts electricity from the external terminal of the battery to the electrode group, and the separator occupied volume accompanying the increase in the area of the electrode or the thinning of the electrode. Accompanied by an increase. As a result, the electrolyte solution injected into the periphery of the electrode group did not penetrate into the electrodes and separators, leaving an unimpregnated portion of the electrolyte solution inside the electrodes. As a result, the rapid charging performance of the battery became unstable and variations were observed.

  Patent Document 2 relates to a battery using an electrode body in which an electrode body layer in which a positive electrode and a negative electrode are opposed to each other via a separator is folded into ninety-nine folds. For each position corresponding to the folded part of the electrode body layer, the active material absence region without applying the positive electrode active material and the negative electrode active material with a certain width (about two layers of the electrode body layer, that is, about 560 μm). Are formed so that the active material non-existing region of the positive electrode and the active material non-existing region of the negative electrode coincide with each other, thereby producing an electrode body in which the electrode body layers are laminated with a uniform thickness.

On the other hand, Patent Document 3 discloses that a separator or a solid electrolyte layer is used by being bent zigzag so as to sew between a positive electrode sheet and a negative electrode sheet. The portion of the separator 3 that covers the uppermost and lowermost negative electrode sheets 2, 2 from above and below has substantially the same width as the width of the negative electrode sheet 2. Further, the separator 3, portion present between the positive electrode sheet 1 and the negative electrode sheet 2 is in the middle of the width W _s of the width W _p and the width W _n of the negative electrode sheet 2 of the positive electrode sheet 1. By adopting such a configuration, the width of the three layers of the positive electrode sheet, the negative electrode sheet, the separator, or the solid electrolyte layer is made the same as the width of the negative electrode sheet, thereby reducing the size of the battery.
JP-A-2005-123183 JP-A-9-7610 JP 2002-329530 A

  In view of such circumstances, an object of the present invention is to provide a nonaqueous electrolyte battery having stable rapid charge / discharge performance with little variation.

The nonaqueous electrolyte battery according to the present invention includes an electrode group having a structure in which a separator is folded back into a ninety-nine shape, and a positive electrode and a negative electrode are alternately inserted in a portion where the separator is doubled, and the separator is folded back. Non-aqueous water comprising: a positive electrode lead drawn out from the side of the positive electrode positioned perpendicular to the end portion; and a negative electrode lead drawn out from the side of the negative electrode positioned perpendicular to the folded end portion of the separator. An electrolyte battery,
The negative electrode includes a negative electrode current collector made of aluminum foil, and a negative electrode active material-containing layer comprising lithium titanium oxide particles having an average particle size of 1 μm or less, carbon powder, and polyvinylidene fluoride carried on the negative electrode current collector. Having a thickness of 40 μm or more and 95 μm or less,
The positive electrode has a positive electrode current collector made of aluminum foil, and a negative electrode active material-containing layer containing lithium cobalt oxide, graphite powder and polyvinylidene fluoride supported on the positive electrode current collector and having a thickness of 35 μm. Above, 90 μm or less,
The separator is made of a polyethylene porous film,
The separator folding width is X, the length of the positive electrode side that is perpendicular to the folding end of the separator is W ₁ , and the length of the negative electrode side that is perpendicular to the folding end of the separator. when the length and _{W 2,} X is in the range range of 68~70mm, _{W 1} in the range of 67~68mm, _{W 2} is 67～88Mm, the following formula (1)

1 mm ≦ {2X− (W ₁ + W ₂ )} ≦ 6 mm (1)
Satisfied,
The positive electrode length indicated by the distance between two sides of the positive electrode positioned perpendicular to the folded end of the separator is L ₁ , and between the two sides of the negative electrode positioned perpendicular to the folded end of the separator When the length of the negative electrode indicated by the distance is L ₂ and the length of the folded end portion of the separator is L ₃ , L ₁ is in the range of 84 to 87 mm, L ₂ is in the range of 83 to 87 mm, and L ₃ is in the range of 89～94Mm, the positive very long of _{L 1} and of the negative very long of _{L 2} than the longer one, the length _{L 3} of the folded end portion of the separator is 2mm or more, 10 mm or less long.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte battery which has the stable rapid charge / discharge performance with few dispersion | variations can be provided.

  In order to increase the size of the electrode group and charge and discharge with a large current, it is desirable to adopt a current collection method in which current is passed from the external terminals of the battery to the electrodes in the electrode group through multiple paths, and a current collector is provided. In addition, a lamination method in which a plurality of single electrodes are laminated to form an electrode group is preferable to the conventional winding method. In addition, various methods can be considered for the electrode stacking method for stacking the electrodes, but the separator opening is larger than the general stacking method in which the electrode plate is inserted into a bag-shaped separator and stacked individually. Large, advantageous in impregnating the electrode with a non-aqueous electrolyte, with a separator folded in a ninety-nine shape between the positive and negative electrodes provided with positive and negative electrode leads as a current collector. Further, it is more preferable to stack electrodes by a separator 99-fold method in which positive and negative electrodes are alternately stacked.

  An example of an electrode group using a separator folded back into a ninety-nine shape is shown in FIGS.

  As shown in FIG. 1, the electrode group 1 includes a negative electrode 2, a positive electrode 3, and a separator 4 disposed between the negative electrode 2 and the positive electrode 3. 2 and 3, the negative electrode 2 includes a strip-shaped negative electrode current collector 2a, a negative electrode lead 5 extending from the vicinity of the center of the short side of the negative electrode current collector 2a, and the negative electrode current collector 2a. And a negative electrode active material-containing layer 2b supported on both sides. 4 and 5, the positive electrode 3 includes a strip-shaped positive electrode current collector 3a, a positive electrode lead 6 extending from the vicinity of the center of the short side of the positive electrode current collector 3a, and a positive electrode current collector. And a positive electrode active material-containing layer 3b supported on both surfaces of 3a. The negative electrode current collector 2a in which the negative electrode lead 5 is integrated and the positive electrode current collector 3a in which the positive electrode lead 6 is integrated are obtained by punching an aluminum plate or an aluminum alloy plate, for example. .

  As shown in FIG. 6, the separator 4 has a belt shape and is folded back into a ninety nine shape. The positive electrode 3 and the negative electrode 2 are alternately inserted between the double separators. The negative electrode 2 is inserted between the double separators 4 so that the short side from which the negative electrode lead 5 extends is positioned perpendicular to the folded end 7 of the separator 4. The tip of the negative electrode lead 5 protrudes from the separator 4. On the other hand, the positive electrode 3 is inserted between the double separators 4 so that the short side from which the positive electrode lead 6 extends is positioned perpendicular to the folded end 7 of the separator 4. The tip of the positive electrode lead 6 also protrudes from the separator 4, but the direction in which the positive electrode lead 6 is drawn from the separator 4 is opposite to the direction in which the negative electrode lead 5 is drawn from the separator 4.

  In order to further develop the advantages of the 99-fold type electrode stacking method, the present inventors have conducted detailed studies on improving the impregnation property of the electrolytic solution. As a result, when the positive electrode 3, the negative electrode 2, and the separator 4 satisfy the following formula (1), the battery has excellent non-aqueous electrolyte impregnation properties, high charge / discharge capacity during rapid charge / discharge, and small variations. It was found that can be obtained.

1 mm ≦ {2X− (W ₁ + W ₂ )} ≦ 6 mm (1)
X is the folding width (mm) of the separator 4 and is the distance between the folding end and the next folding end. W ₁ is the length (mm) of the side of the positive electrode 3 positioned perpendicular to the folded end 7 of the separator 4, and is equal to the length of the short side of the positive electrode 3 in FIG. W ₂ is the length (mm) of the side of the negative electrode 2 positioned perpendicular to the folded end 7 of the separator 4, and is equal to the length of the short side of the negative electrode 2 in FIG.

By making {2X− (W ₁ + W ₂ )} 1 mm or more, the end faces of the positive electrode and the negative electrode are surrounded by a gap between the folded portions of the separator. The remaining air is discharged smoothly, and the impregnation with the electrolyte can proceed smoothly. Further, by setting {2X− (W ₁ + W ₂ )} to 6 mm or less, it is possible to suppress a decrease in energy density caused by providing a gap between the end faces of the positive electrode and the negative electrode and the folded portion of the separator. A more preferable range of {2X− (W ₁ + W ₂ )} is 2 mm or more and 4 mm or less.

In order to sufficiently obtain the effect of the above expression (1), X is 60 mm or more and 120 mm or less, W ₁ is 59.5 mm or more and 119.5 mm or less, and W ₂ is 59.5 mm or more and 119. It is desirable that it is 5 mm or less.

In addition, in applying the 99-fold type electrode group to a large battery, a safety test was conducted and confirmed. As a result, the positive electrode length L ₁ (shown in FIGS. 1 and 4) indicated by the side opposite to the side from which the positive electrode lead 6 is drawn and the negative side indicated by the side opposite to the side from which the negative electrode lead 5 is drawn. The length L ₃ (shown in FIG. 1) of the folded end portion of the separator 4 is increased by 2 mm or more and 10 mm or less compared to the longer one of the length L ₂ (shown in FIGS. 1 and 2). Accordingly, it is possible to prevent a short circuit between the positive and negative electrode leads that occurs due to the shrinkage of the separator even under an abnormally high temperature. Further, when the positive electrode length L ₁ and the negative electrode length L ₂ are equal, the length L ₃ of the folded end of the separator 4 is set to be longer than both the positive electrode length L ₁ and the negative electrode length L _2. By increasing the length by 2 mm or more and 10 mm or less, it is possible to prevent a short circuit between the positive and negative electrode leads caused by the shrinkage of the separator even under an abnormally high temperature. In any case, if the length L ₃ of the folded end of the separator is made longer than 10 mm, the volumetric efficiency of the battery may be reduced. A more preferable range is 3 mm or more and 7 mm or less. As long as the above relationship is satisfied, the distance from one side of the positive electrode to the folded end of the separator and the distance from the other side of the positive electrode to the folded end of the separator are the same or different, and the short circuit prevention effect Can be obtained. The same applies to the negative electrode.

In the non-aqueous electrolyte battery satisfying the above-described formula (1), it is desirable that the positive electrode thickness t ₁ is 35 μm or more and 90 μm or less, and the negative electrode thickness t ₂ is 40 μm or more and 95 μm or less. Although a thinner positive electrode and negative electrode are advantageous for impregnation with the non-aqueous electrolyte, variations in the thickness of the active material-containing layer of the positive electrode and the negative electrode are increased. By making the thickness of the positive electrode 35 μm or more and 90 μm or less and the thickness of the negative electrode 40 μm or more and 95 μm or less, there is no problem of variation in the thickness of the active material containing layer of the positive and negative electrodes. The impregnation property of the nonaqueous electrolytic solution can be further improved.

  In addition, the thickness of a positive electrode and a negative electrode is measured with a micrometer.

  A container in which the electrode group 1 of FIG. 1 is housed is shown in FIG. As shown in FIG. 7, the container 8 is formed by subjecting the laminate film to an electrode group housing portion 9 composed of a rectangular recess formed by, for example, deep drawing or pressing, and processing of the laminate film. And a rectangular lid 10 formed of a flat plate portion that is not formed. When the laminate film is folded back along the dotted line toward the container, the electrode group storage unit 9 can be covered with the lid 10. The inner surface of the lid body 10 is bonded to the three sides 11a to 11c at the periphery of the opening of the electrode group storage portion 9 by, for example, heat sealing. FIG. 8 shows a state in which the lid body 10 is joined to the three sides 11 a to 11 c at the periphery of the opening of the electrode group storage portion 9 and arranged with the lid body 10 facing down. As the laminate film, for example, a laminate film in which a metal layer is disposed between a thermoplastic resin layer and a resin layer can be used. Since the thermoplastic resin layer is positioned on the inner surfaces of the electrode group housing portion 9 and the lid body 10, the lid body 10 can be joined to the electrode group housing portion 9 by thermal fusion. The thermoplastic resin layer is made of, for example, polypropylene (PP) or polyethylene (PE). The metal layer is preferably an aluminum foil or an aluminum alloy foil. The resin layer is used to reinforce the metal layer and can be formed from a polymer such as nylon or polyethylene terephthalate (PET).

  The electrode group 1 is stored in the electrode group storage portion 9 of the container 8 while holding the nonaqueous electrolyte. The positive electrode lead 6 is welded to the positive electrode tab 12 in a bundled state. The negative electrode lead 5 is welded to the negative electrode tab 13 in a bundled state. The positive electrode tab 12 and the negative electrode tab 13 are made of a conductive material such as aluminum or an aluminum alloy, for example. As shown in FIG. 8, the positive electrode tab 12 is drawn to the outside from between the short side 11 a around the opening of the electrode group housing portion 9 and the lid 10. The negative electrode tab 13 is drawn out from between the short side 11 b on the opposite side of the periphery of the opening of the electrode group storage unit 9 and the lid 10. The long side 11c at the periphery of the opening of the electrode group storage unit 9 and the lid 10 are joined by heat fusion and then bent substantially vertically. In FIG. 8, the positive and negative electrode tabs are welded to the positive and negative electrode leads, and the positive and negative electrode tabs are pulled out from the container. However, the positive and negative electrode leads can be pulled out from the container as they are.

  In FIG. 1 described above, the direction in which the positive electrode lead is drawn out and the direction in which the negative electrode lead is drawn are opposite to each other, but the direction in which the positive electrode lead is drawn out and the direction in which the negative electrode lead is drawn out are the same direction, that is, the positive electrode lead from the same end face of the electrode group. In addition, the negative electrode lead may be pulled out.

  Hereinafter, the negative electrode, the positive electrode, the separator, and the nonaqueous electrolyte will be described.

1) Negative electrode The negative electrode includes a negative electrode current collector and a negative electrode active material-containing layer that is supported on one or both surfaces of the negative electrode current collector and includes a negative electrode active material, a conductive agent, and a binder.

  An aluminum foil or an aluminum alloy foil can be used for the negative electrode current collector. The average crystal grain size of the aluminum foil and the aluminum alloy foil is desirably 50 μm or less. When the range of the average crystal grain size is 50 μm or less, the strength of the aluminum foil or aluminum alloy foil can be dramatically increased. This increase in the strength of the negative electrode current collector improves physical and chemical stability and makes it difficult for the negative electrode current collector to break. In particular, it is possible to prevent deterioration due to dissolution of the negative electrode current collector, which is remarkable in an overdischarge long-term cycle under a high temperature environment of 40 ° C. or higher, and it is possible to suppress an increase in electrode resistance. Furthermore, by suppressing an increase in electrode resistance, Joule heat is reduced, and heat generation of the electrode can be suppressed. Further, the increase in the strength of the negative electrode current collector makes it possible to increase the density of the negative electrode without interrupting the negative electrode current collector, thereby improving the capacity density. In addition, increasing the density of the negative electrode increases the thermal conductivity and improves the heat dissipation of the electrode. Furthermore, the rise in battery temperature can be suppressed by the synergistic effect of suppressing the heat generation of the battery and improving the heat dissipation of the electrode. A more preferable average crystal grain size is 3 μm or less. This further increases the above-described effect. The smaller the average grain size, the higher the chemical and physical strength of the negative electrode current collector. The lower limit of is desirably 0.01 μm.

  Aluminum foil or aluminum alloy foil having an average crystal grain size range of 50 μm or less is affected by factors such as material composition, processing conditions, heating conditions, and cooling conditions in a complicated manner. It is adjusted by organically combining various factors. In addition, you may use the high performance aluminum foil PACAL21 (brand name) made from Japanese foil as an aluminum foil of a negative electrode collector. Specifically, an aluminum foil with an average crystal grain size of 50 μm or less can be produced by annealing an aluminum foil with an average crystal grain size of 90 μm at 50 to 250 ° C. and then cooling to room temperature. On the other hand, an aluminum alloy foil having an average crystal grain size of 50 μm or less can be produced by annealing an aluminum alloy foil having an average crystal grain size of 90 μm at 50 to 250 ° C. and then cooling to room temperature. Alternatively, an aluminum alloy foil having an average crystal grain size of 50 μm or less can also be produced by annealing an alloy containing 0.8 to 2% by weight of Fe.

The average crystal grain size of aluminum and aluminum alloy is measured by the method described below. The structure of the current collector surface is observed with a metal microscope, the number n of crystal grains existing in a 1 mm × 1 mm visual field is measured, and the average crystal grain area S (μm ² ) is calculated from the following formula (A).

S = (1 × 10 ⁶ ) / n (A)
Here, the value represented by (1 × 10 ⁶ ) is a visual field area (μm ² ) of 1 mm × 1 mm, and n is the number of crystal grains. The average crystal grain size d (μm) was calculated from the following formula (B) using the obtained average crystal grain area S. Such calculation of the average crystal grain size d was performed for five locations (five fields of view), and the average value was defined as the average crystal grain size. Note that the assumed error is about 5%.

d = 2 (S / π) ^1/2 (B)
The thickness of the negative electrode current collector is preferably 20 μm or less in order to increase the capacity. A more preferable range is 12 μm or less. Further, the lower limit value of the thickness of the negative electrode current collector is desirably 3 μm.

  The purity of aluminum used for the negative electrode current collector is preferably 99.99% or more for improving corrosion resistance and increasing strength. The aluminum alloy is preferably an alloy containing one or more elements selected from the group consisting of iron, magnesium, zinc, manganese and silicon in addition to aluminum. For example, an Al-Fe alloy, an Al-Mn alloy, and an Al-Mg alloy can obtain higher strength than aluminum. On the other hand, the content of transition metals such as nickel and chromium in aluminum and aluminum alloys is preferably 100 ppm or less (including 0 ppm). For example, an Al—Cu-based alloy increases strength but deteriorates corrosion resistance, and is not suitable as a current collector. The aluminum content in the aluminum alloy is desirably 95% by weight or more and 99.5% by weight or less. If it is out of this range, sufficient strength may not be obtained even if the average crystal grain size is 50 μm or less. A more preferable aluminum content is 98% by weight or more and 99.5% by weight or less.

  The average particle size of the negative electrode active material is desirably 1 μm or less. Thereby, quick charge performance can further be improved. A more preferable average particle diameter is 0.3 μm or less. However, if the average particle size is small, the aggregation of primary particles tends to occur, or the nonaqueous electrolyte distribution may be biased toward the negative electrode, leading to depletion of the electrolyte at the positive electrode, so the lower limit is set to 0.001 μm. It is desirable to do. In general, during the electrode pressing step, the smaller the average particle size of the active material, the greater the load on the current collector. Since this negative electrode active material has an average particle size of 1 μm or less, the load applied to the negative electrode current collector is also large. However, since the aluminum foil or aluminum alloy foil having an average crystal grain size in the range of 50 μm or less as the negative electrode current collector has high strength, it can withstand a strong load caused by particles having an average grain size of 1 μm or less.

  A negative electrode active material having an average particle size of 1 μm or less is obtained by reacting and synthesizing active material raw materials to produce an active material precursor, followed by firing treatment and grinding treatment using a grinding machine such as a ball mill or a jet mill. It is done. In the baking treatment, a part of the active material precursor may be aggregated to grow into secondary particles having a large particle size. For this reason, it is permitted that the negative electrode active material contains secondary particles. Since a substance having a smaller particle diameter is easier to grind, the active material precursor is preferably a powder of 1 μm or less.

  As the negative electrode active material, a material that absorbs and releases lithium can be used, and examples thereof include carbonaceous materials, metal oxides, metal sulfides, metal nitrides, and alloys.

  Examples of the carbonaceous material include a graphite material or a carbonaceous material (for example, graphite, coke, carbon fiber, spherical carbon, pyrolytic gas phase carbonaceous material, resin fired body, and the like).

  The lithium occlusion potential of the negative electrode active material is preferably 0.4 V or more in terms of open circuit potential relative to the open circuit potential of lithium metal. Thereby, the progress of the alloying reaction between the aluminum component of the negative electrode current collector and lithium and the pulverization of the negative electrode current collector can be suppressed. Furthermore, the lithium occlusion potential is preferably in the range of 0.4 V or more and 3 V or less as an open circuit potential with respect to the open circuit potential of lithium metal. Thereby, a battery voltage can be improved. A more preferable potential range is 0.4 V or more and 2 V or less.

As a metal oxide capable of occluding lithium in the range of 0.4 V or more and 3 V or less, for example, a titanium oxide such as TiO ₂ , for example, Li _{4 + x} Ti ₅ O ₁₂ (x is −1 ≦ x ≦ 3) and lithium titanium oxides such as Li ₂ Ti ₃ O ₇ , tungsten oxides such as WO ₃ , amorphous tin oxides such as SnB _0.4 P _0.6 O _3.1 , tin silicon oxides such as SnSiO _3, etc. Examples thereof include silicon oxide such as SiO.

Examples of the metal sulfide capable of occluding lithium in the range of 0.4 V or more and 3 V or less include lithium sulfide such as TiS ₂ , molybdenum sulfide such as MoS ₂ , such as FeS, FeS ₂ , and Li _x FeS _2. And iron sulfide.

Examples of the metal nitride capable of occluding lithium in the range of 0.4 V or more and 3 V or less include lithium cobalt nitride such as Li _x Co _y N (0 <x <4, 0 <y <0.5). Thing etc. are mentioned.

  As the negative electrode active material, lithium titanate is preferable. Thereby, the quick charge performance can be further improved.

  A carbon material can be used as a conductive agent for increasing electron conductivity and suppressing contact resistance with the current collector. Examples thereof include acetylene black, carbon black, coke, carbon fiber, and graphite.

  Examples of the binder for binding the active material and the conductive agent include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, and styrene butadiene rubber.

  Regarding the mixing ratio of the negative electrode active material, the conductive agent, and the binder, the negative electrode active material is 80% by weight to 95% by weight, the conductive agent is 3% by weight to 18% by weight, and the binder is 2% by weight or more. It is preferable to make it into the range of 7 weight% or less.

The density of the negative electrode is desirably 1.5 g / cm ³ or more and 5 g / cm ³ or less. Thereby, a high battery capacity can be obtained. A more preferable range is 2 g / cm ³ or more and 4 g / cm ³ or less.

  For example, a negative electrode active material, a conductive agent, and a binder are suspended in an appropriate solvent, and the suspension is applied to a current collector and then dried to form a negative electrode active material-containing layer on the current collector. These are produced by pressing them.

2) Positive electrode The positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer that is supported on one or both surfaces of the positive electrode current collector and includes a positive electrode active material, a conductive agent, and a binder.

  Examples of the positive electrode current collector include an aluminum foil and an aluminum alloy foil. Each of the aluminum foil and the aluminum alloy foil preferably has an average crystal grain size of 50 μm or less. More preferably, it is 3 μm or less. As a result, the strength of the positive electrode current collector is increased, the positive electrode can be densified without breaking the positive electrode current collector, and the capacity density can be improved. As the average crystal grain size is smaller, the occurrence of pin poles and cracks can be reduced, and the chemical strength and physical strength of the positive electrode current collector can be increased. In order to secure an appropriate hardness by setting the microstructure of the current collector to be crystalline, the lower limit value of the average crystal grain size is desirably 0.01 μm.

  The thickness of the positive electrode current collector is preferably 20 μm or less in order to increase the capacity. A more preferable range is 15 μm or less. Moreover, it is desirable that the lower limit value of the thickness of the positive electrode current collector be 3 μm.

Examples of the positive electrode active material include oxides, sulfides, and polymers. As the oxide, for example, manganese dioxide (MnO ₂ ), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide such as Li _x Mn ₂ O ₄ or Li _x MnO ₂ , lithium such as Li _x NiO _2, etc. nickel composite oxide, for example, Li _x lithium-cobalt composite oxides such as CoO _2, for example, LiNi _1-y Co _y O ₂ lithium-nickel-cobalt composite oxide such as, for example, lithium manganese cobalt such as LiMn _y Co _1-y O ₂ composite oxides, for example olivine, such as _{Li x Mn 2-y Ni y} O 4 spinel-type lithium-manganese-nickel composite oxide such as, for example, _{Li x FePO 4, Li x Fe} 1-y Mn y PO 4, Li x CoPO 4 Lithium phosphorus oxide having a structure, for example, iron sulfate such as Fe ₂ (SO ₄ ) ₃ , for example, vanadium oxide such as V ₂ O ₅ And so on. In addition, it is preferable that x and y are the range of 0-1.

  Examples of the polymer include conductive polymer materials such as polyaniline and polypyrrole, and disulfide polymer materials. In addition, sulfur (S), carbon fluoride, and the like can be used. Preferred positive electrode active materials include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, spinel type lithium manganese nickel composite oxide, lithium manganese cobalt composite oxide, lithium phosphorus Examples include acid iron. According to these active materials, a high positive electrode voltage can be obtained.

  Examples of the conductive agent for increasing the electron conductivity and suppressing the contact resistance with the current collector include acetylene black, carbon black, and graphite.

  Examples of the binder for binding the active material and the conductive agent include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine-based rubber.

  Regarding the mixing ratio of the positive electrode active material, the conductive agent and the binder, the positive electrode active material is 80% by weight to 95% by weight, the conductive agent is 3% by weight to 18% by weight, and the binder is 2% by weight to 7%. It is preferable to make it into the range below weight%.

  In the positive electrode, for example, the positive electrode active material, the conductive agent and the binder are suspended in an appropriate solvent, and the suspension is applied to the positive electrode current collector and then dried to form a positive electrode active material-containing layer on the current collector. It is produced by forming and pressing them.

3) Nonaqueous electrolyte The nonaqueous electrolyte is prepared, for example, by dissolving an electrolyte in an organic solvent. Moreover, you may use the normal temperature molten salt (ionic melt) containing lithium ion as a non-aqueous electrolyte.

Examples of the electrolyte include LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Li (CF ₃ SO ₂ ). ₃ C, LiB [(OCO) ₂ ] _{2 and the} like. The type of electrolyte used can be one type or two or more types.

  The electrolyte concentration in the organic solvent is desirably in the range of 0.5 to 2 mol / L.

  Examples of the organic solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC), dimethoxyethane ( Examples thereof include chain ethers such as DME) and dietoethane (DEE), cyclic ethers such as tetrahydrofuran (THF) and dioxolane (DOX), γ-butyrolactone (GBL), acetonitrile (AN) and sulfolane (SL). These organic solvents can be used alone or in the form of a mixture of two or more.

  The room temperature molten salt (ionic melt) is preferably composed of lithium ions, organic cations and organic anions. The room temperature molten salt is desirably in a liquid state at 100 ° C. or less, preferably at room temperature or less.

4) Separator As the separator, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or the like can be used.

5) Container It is desirable that the thickness of the laminate film constituting the laminate film container is 0.5 mm or less. Moreover, it is desirable that the lower limit value of the thickness of the laminate film be 0.01 mm.

  As the container, a metal container may be used instead of the laminate film container illustrated in FIG. 7 described above. The thickness of the metal container is desirably 0.5 mm or less. The lower limit of the metal container is desirably 0.05 mm.

  The metal container is preferably made of aluminum or an aluminum alloy. The average crystal grain size of each of aluminum and aluminum alloy is preferably 50 μm or less. By setting the average crystal grain size to 50 μm or less, the strength of a metal container made of aluminum or an aluminum alloy is increased, and sufficient mechanical strength can be ensured even if the thickness of the container is reduced. In addition, More preferably, it is 10 micrometers or less. Further, it is desirable that the lower limit value of the average crystal grain size is 0.01 μm. These features are suitable for batteries that require high temperature conditions, high energy density, etc., for example, in-vehicle secondary batteries. For the same reason as the negative electrode current collector, the purity of aluminum is preferably 99.99% or more. As the aluminum alloy, an alloy containing elements such as magnesium, zinc, and silicon is preferable. On the other hand, it is preferable that the content of transition metals such as iron, copper, nickel, and chromium in aluminum and aluminum alloy is 100 ppm or less. The metal container can be sealed with a laser.

  The shape of the container depends on the form of the nonaqueous electrolyte battery. Examples of the nonaqueous electrolyte battery include a flat battery, a square battery, a sheet battery, a large battery mounted on an electric vehicle, and the like.

[Example]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

Example 1
<Production of negative electrode>
As an active material, lithium titanate (Li ₄ Ti ₅ O ₁₂ ) powder having an average particle diameter of 1 μm and a Li occlusion potential of 1.55 V (vs. Li / Li ⁺ ), and carbon having an average particle diameter of 0.4 μm as a conductive agent. The powder and polyvinylidene fluoride (PVdF) as a binder were blended in a weight ratio of 90: 7: 3, and these were dispersed in an n-methylpyrrolidone (NMP) solvent to prepare a slurry. On the other hand, an aluminum foil (purity 99.99%) having a thickness of 10 μm and an average crystal grain size of 50 μm was prepared as a negative electrode current collector. The slurry was applied to both sides except for both ends of the obtained negative electrode current collector, dried, and then pressed to produce a negative electrode. By punching the obtained negative electrode, a strip-shaped negative electrode having a negative electrode lead on the short side was obtained. The obtained negative electrode had a thickness of 70 μm and an electrode density of 2.4 g / cm ³ .

  In addition, the laser diffraction type particle size distribution measuring apparatus (Shimadzu Corporation model number SALD-300) was used for the measurement of the particle diameter of a negative electrode active material. First, about 0.1 g of a sample was put in a beaker or the like, and then a surfactant and 1 to 2 mL of distilled water were added and stirred sufficiently, and poured into a stirred water tank. The light intensity distribution was measured 64 times at intervals of 2 seconds, the particle size distribution data was analyzed, and the particle size (D50) having a cumulative frequency distribution of 50% was defined as the average particle size.

<Preparation of positive electrode>
Lithium cobalt oxide (LiCoO ₂ ) as an active material, graphite powder as a conductive material, and polyvinylidene fluoride (PVdF) as a binder are blended so that the weight ratio is 87: 8: 5, and these are n -A slurry was prepared by dispersing in a methylpyrrolidone (NMP) solvent. A slurry was applied to both surfaces except for both ends of an aluminum foil (purity 99.99%) having an average crystal grain size of 10 μm with a thickness of 15 μm, dried, and then pressed to prepare a positive electrode. By punching the obtained positive electrode, a strip-shaped positive electrode having a positive electrode lead on the short side was obtained. The thickness of the positive electrode was 60 μm, and the electrode density was 3.5 g / cm ³ .

  As a forming material for the container (exterior member), an aluminum-containing laminate film having a thickness of 0.1 mm was prepared. The aluminum layer of this aluminum-containing laminate film had a film thickness of about 0.03 mm and an average crystal grain size of about 100 μm. Polyethylene was used as the resin for reinforcing the aluminum layer. By forming a rectangular recess in this laminate film, a container (exterior member) as shown in FIG. 7 was obtained.

  Next, as shown in FIG. 6, after placing the positive electrode on one side of a continuous separator made of a polyethylene porous film having a thickness of 25 μm, the positive electrode was covered by folding the separator, and was superimposed on the positive electrode. A negative electrode was placed on the separator. The separator was further folded to cover the negative electrode, and the positive electrode was placed on the separator superimposed on the negative electrode. In this way, the separator was folded back into a ninety-nine shape to obtain a stacked electrode group. At this time, the positive electrode lead and the negative electrode lead protruded from the side perpendicular to the folded end portion of the separator, and the protruding direction of the positive electrode lead and the protruding direction of the negative electrode lead were opposite to each other. Further, the positive electrode lead was welded to the positive electrode tab in a bundled state, and the negative electrode lead was welded to the negative electrode tab in a bundled state.

Wrap width of the separator 4 in the obtained electrode group X (mm), the length of the short side of the positive electrode 3 W ₁ (mm), the length of the short side of the negative electrode _{2 W 2 (mm), {} 2X- (W 1 + W ₂ )} is shown in Table 1 below. Further, the positive electrode length L ₁ indicated by the side where the positive electrode lead 6 was drawn out and the side facing each other was 87 mm. The negative electrode length L ₂ indicated by the side from which the negative electrode lead 5 was drawn out and the side opposite to the side was 87 mm. The length of the folded end portion of the separator 4 (the length of the long side of the separator 4) L ₃ was 92 mm. Since the positive electrode length L ₁ and the negative electrode length L ₂ are equal, the difference between the length L ₃ of the folded end portion of the separator 4 is 5 mm. For convenience, the difference between the positive electrode length L ₁ and the length L ₃ of the folded end of the separator 4 is shown in Table 1.

The electrode group was inserted into the recess of the container (exterior member). Lithium salt LiBF ₄ was dissolved in an organic solvent in which EC and GBL were mixed at a volume ratio (EC: GBL) of 1: 2 to prepare a nonaqueous electrolytic solution. The obtained non-aqueous electrolyte was poured into a container, and had the structure shown in FIGS. 1 to 8 described above, a flat type non-water having a thickness of 6 mm, a length of 120 mm (excluding the lead portion), and a width of 76 mm. An electrolyte battery was produced.

(Examples 2-8 and Comparative Examples 3-6)
A non-aqueous electrolyte battery is formed in the same manner as described in Example 1 except that X, W ₁ , W ₂ , {2X− (W ₁ + W ₂ )} are set to the values shown in Table 1 below. Produced.

(Comparative Example 1)
A negative electrode slurry prepared in the same manner as described in Example 1 was applied to a negative electrode current collector similar to that described in Example 1, dried, and then pressed to prepare a negative electrode. Further, a positive electrode slurry prepared in the same manner as described in Example 1 was applied to a positive electrode current collector similar to that described in Example 1, dried, and then pressed to produce a positive electrode. did.

  A separator made of a polyethylene porous film having a thickness of 25 μm was interposed between the produced positive electrode and negative electrode, and these were wound into a flat spiral shape to obtain an electrode group. The positive electrode lead was drawn out from one end face of the obtained electrode group, and the negative electrode lead was drawn out from the other end face. A nonaqueous electrolyte battery was produced in the same manner as described in Example 1 except that such an electrode group was used.

(Comparative Example 2)
A negative electrode produced in the same manner as described in Example 1 was stored in a bag-like separator made of a polyethylene porous film so that the negative electrode lead protruded from the opening of the separator. The negative electrode accommodated in this separator and the positive electrode produced in the same manner as described in Example 1 were alternately laminated. At that time, the negative electrode lead protruded from the positive electrode on one short side of the laminate, and the positive electrode lead protruded from the negative electrode on the other short side. In the obtained electrode group, the short side length W _{1 of} the positive electrode, the short side length W ₂ of the negative electrode, X (the width in the short side direction of the bag separator is regarded as X), {2X− (W ₁ + W ₂ )} is shown in Table 1 below.

  A nonaqueous electrolyte battery was produced in the same manner as described in Example 1 except that the obtained electrode group was used.

In the obtained battery, the battery was stored under a high pressure of 0.5 MPa for 12 hours so that the electrolyte solution was sufficiently impregnated in the battery electrode group. The impregnated area ratio was measured and the results are shown in Table 1 below. FIG. 9 shows the relationship between {2X− (W ₁ + W ₂ )} and 15 A discharge capacity.

<Measurement of 15A discharge capacity>
The obtained battery was charged at a constant voltage and a constant voltage for 3 hours under the conditions of a charging voltage of 2.8 V and a charging current of 3 A, and then subjected to a discharge test at a current of 15 A to obtain a discharge capacity until reaching a final voltage of 1.5 V It was.

<Evaluation of quick charge performance>
The battery was again discharged to 1.5 V with a current of 3 A, and then rapidly charged for 20 minutes under the conditions of a charging voltage of 2.8 V and a charging current of 30 A. Thereafter, the discharge capacity until reaching 1.5 V with a current of 15 A was measured, and the ratio with the previously implemented 15 A discharge capacity was determined.

<Measurement of electrolyte impregnation rate into separator>
After finishing the test so far, the battery was disassembled, the separator was taken out from the electrode group, and the impregnation rate of the electrolyte into the separator was investigated. The image of the separator was captured with an OMRON microscope, the unimpregnated portion was selected, and the area was calculated. The remaining area was regarded as the impregnation part, and this was divided by the total area of the separator to obtain the impregnation rate.

  As can be seen from Table 1, in the batteries of Examples 1 to 8 that satisfy the above-described formula (1), the 15A discharge capacity is higher than that of Comparative Examples 1 to 6. Moreover, as shown in FIG. 9, the discharge capacities of the batteries of Examples 1 to 8 are concentrated in the range of 3000 to 3100 mAh, and variation is small. In addition, it can be seen that the discharge capacity ratio does not decrease much even after discharge after rapid charge, and has excellent rapid charge performance.

On the other hand, in Comparative Example 1 using a wound electrode group, Comparative Example 2 using a bag-shaped separator, and Comparative Examples 3 and 4 where {2X− (W ₁ + W ₂ )} is 0 mm, the separator electrolyte solution The impregnation rate, 15A discharge capacity, and discharge capacity ratio after rapid charging are all low. Further, according to Comparative Examples 5 and 6 in which the value of {2X− (W ₁ + W ₂ )} exceeds 6 mm, the 15 A discharge capacity was lowered although the electrolyte solution impregnation rate of the separator was high.

(Examples 9 to 13)
Except that the positive electrode length L ₁ , the negative electrode length L ₂ , and the length L ₃ of the folded end of the separator 4 are set as shown in Table 2 below, the same as described in Example 1 above. A nonaqueous electrolyte battery was produced. Regarding Examples 9 to 12, since the positive electrode length L ₁ and the negative electrode length L ₂ are equal, the difference between the positive electrode length L ₁ and the length L ₃ of the folded end portion of the separator 4 is shown in Table 1 for convenience. . In Example 13, since the positive electrode length L ₁ is longer than the negative electrode length L ₂ , the difference between the positive electrode length L ₁ and the length L ₃ of the folded end of the separator 4 is shown in Table 1. Show.

  The safety of the obtained battery was evaluated by the method described below, and the results are shown in Table 2 below. Table 2 also shows the results of Example 1 described above.

<Safety test>
For each of the 10 batteries of Example 1 and Examples 9 to 13, a high temperature overheating test was performed in which the temperature was increased from room temperature to 150 ° C. at a rate of 5 ° C./min, and then maintained at 150 ° C. for 10 minutes. did. Table 2 shows the presence / absence of battery rupture / ignition and the number of short circuits. All batteries were safe without rupture or ignition. However, in the battery of Example 9, a voltage drop was observed in 1 of 10 batteries. As a result of disassembling the battery, it was confirmed that the separator contracted at the lead portions of the positive and negative electrodes, and in particular, the negative electrode end was exposed from the separator at the positive electrode lead portion and the positive and negative electrodes were short-circuited. In other batteries than Example 9, the separator was similarly contracted, but the electrode end was not exposed from the separator.

As is apparent from Table 2, the battery of this example is safe without being ruptured or ignited even when placed at a high temperature. In particular short circuit in the batteries of Examples 1 and 10 to 13 the length L ₃ of the folded end portion of the separator with respect to the electrode length is not less than 3mm does not occur, it can be said to be more secure.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The top view which shows the electrode group used for the nonaqueous electrolyte battery which concerns on embodiment of this invention. The top view of the negative electrode used for the electrode group of FIG. Sectional drawing obtained when the negative electrode of FIG. 2 is cut | disconnected in the thickness direction. The top view of the positive electrode used for the electrode group of FIG. Sectional drawing obtained when the positive electrode of FIG. 4 is cut | disconnected in the thickness direction. The perspective view for demonstrating the preparation methods of the electrode group of FIG. The perspective view which shows the container in which the electrode group of FIG. 1 is accommodated. The perspective view which shows the nonaqueous electrolyte battery which concerns on embodiment of this invention. The characteristic view which shows the relationship between {2X- (W < ₁ > + W < ₂ >)} and 15A discharge capacity about Examples 1-8 and Comparative Examples 1-6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electrode group, 2 ... Negative electrode, 2a ... Negative electrode collector, 2b ... Negative electrode active material containing layer, 3 ... Positive electrode, 3a ... Positive electrode collector, 3b ... Positive electrode active material containing layer, 4 ... Separator, 5 ... Negative electrode Lead, 6 ... Positive electrode lead, 7 ... Folded end, 8 ... Container, 9 ... Electrode group housing part, 10 ... Lid, 12 ... Positive electrode tab, 13 ... Negative electrode tab.

Claims (1)

The separator is folded into a ninety-nine shape, and a positive electrode and a negative electrode are alternately inserted into a portion where the separator is doubled, and the separator is positioned perpendicular to the folded end of the separator. A non-aqueous electrolyte battery comprising a positive electrode lead drawn from the side of the positive electrode and a negative electrode lead drawn from the side of the negative electrode positioned perpendicular to the folded end of the separator,
The negative electrode includes a negative electrode current collector made of aluminum foil, and a negative electrode active material-containing layer comprising lithium titanium oxide particles having an average particle size of 1 μm or less, carbon powder, and polyvinylidene fluoride carried on the negative electrode current collector. Having a thickness of 40 μm or more and 95 μm or less,
The positive electrode has a positive electrode current collector made of aluminum foil, and a negative electrode active material-containing layer containing lithium cobalt oxide, graphite powder and polyvinylidene fluoride supported on the positive electrode current collector and having a thickness of 35 μm. Above, 90 μm or less,
The separator is made of a polyethylene porous film,
The separator folding width is X, the length of the positive electrode side that is perpendicular to the folding end of the separator is W ₁ , and the length of the negative electrode side that is perpendicular to the folding end of the separator. When the length is W ₂ , X is in the range of 68 to 70 mm, W ₁ is in the range of 67 to 68 mm, and W ₂ is in the range of 67 to 88 mm. The following formula (1) 1 mm ≦ {2X− (W ₁ + W ₂ )} ≦ 6 mm (1)
Satisfied,
The positive electrode length indicated by the distance between two sides of the positive electrode positioned perpendicular to the folded end of the separator is L ₁ , and between the two sides of the negative electrode positioned perpendicular to the folded end of the separator When the length of the negative electrode indicated by the distance is L ₂ and the length of the folded end portion of the separator is L ₃ , L ₁ is in the range of 84 to 87 mm, L ₂ is in the range of 83 to 87 mm, and L ₃ is in the range of 89～94Mm, the positive very long of _{L 1} and of the negative very long of _{L 2} than the longer one, the length _{L 3} of the folded end portion of the separator is 2mm or more, 10 mm or less A nonaqueous electrolyte battery characterized by its long length.

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