JP2011210995A - Storage device - Google Patents

Abstract

An electric storage device capable of shortening a pre-doping time is provided.
A lithium ion capacitor 10 as an electricity storage device includes an electrode stacking unit in which positive electrodes 11 and negative electrodes 12 are alternately stacked via separators 13, and lithium including metal lithium that pre-doped lithium ions on the negative electrode 12. It consists of poles. Through holes 11c and 12c are formed in the positive electrode current collector 11b and the negative electrode current collector 12b. The average hole diameter (a) of the through holes 11c and 12c is 1 to 1000 μm, and the electrode thickness L is defined by the sum of the thickness of the separator 13 and the value of half the thickness of the positive electrode 11 and the negative electrode 12. The ratio b / a with the average value (b) is in the range of 0.08 to 530. As described above, since the diameter of the through hole is set within a predetermined range and the hole diameter and the thickness of the electrode satisfy the predetermined relationship, it is possible to shorten the movement distance of the lithium ion.
[Selection] Figure 2

Description

  The present invention relates to a storage device technology, and is particularly effective when applied to a device including a lithium ion supply source that supplies lithium ions pre-doped to an electrode.

  In recent years, environmental problems with respect to vehicle exhaust gas and the like have been highlighted. Therefore, environmentally friendly electric vehicles and the like are being developed. In the development of electric vehicles, the development of power storage devices as power sources is particularly active. Therefore, various types of power storage devices have been proposed in place of the conventional lead storage battery.

  Examples of the electricity storage device include a lithium ion secondary battery and an electric double layer capacitor. In particular, a hybrid capacitor including a lithium ion capacitor in which a negative electrode is previously doped with lithium ions (pre-doped) is currently attracting attention. Pre-doped hybrid capacitors are partly installed in actual vehicles, and implementation tests are being conducted for their practical use.

  In this pre-doped hybrid capacitor, a porous current collector in which a through-hole penetrating the front and back surfaces of the current collector is formed so that lithium ions in the electrolytic solution can pass through the current collector. The aperture ratio of the porous current collector is usually about 40 to 60% from the viewpoint of appropriately and easily passing lithium ions (see, for example, Patent Documents 1 and 2).

  Various proposals have been made to form through-holes in a current collector other than pre-doped type electricity storage devices. For example, in Patent Document 3, for the purpose of improving the uniformity of cell characteristics and quality, the thickness of the current collector is 0.005 to 0.05 mm, and the current collector has a diameter of 0.01 to 1 mm. A sealed battery having a through hole has been proposed. In Patent Document 4, for the purpose of facilitating the extraction of the plasticizer, the diameter and pitch of the through holes are set in a predetermined relationship, and preferably the thickness of the current collector and the thickness of the active material layer are set in a predetermined relationship. Secondary batteries and the like have been proposed. In addition, various proposals have been made to set the sizes of the through holes and the thickness of the electrodes within a predetermined range (see Patent Documents 5 to 7).

JP 2007-141897 A JP 2009-199963 A JP-A-9-161805 JP 2000-311693 A Japanese Patent No. 4352972 JP 2008-269890 A JP 2005-294168 A

  However, in the pre-doped power storage device, the movement distance of the lithium ion in the horizontal (diameter) direction increases as the hole diameter of the through hole increases. Further, as the thickness of the electrode is increased, the moving distance of lithium ions in the vertical (thickness) direction increases. Therefore, in any case, the movement distance of lithium ions becomes long, and it takes time for diffusion and the pre-doping time becomes long. If the pre-doping time becomes long, the unstable state is left for a long time, which easily causes various problems such as gas generation, non-uniform pre-doping (potential variation), and micro-short due to lithium deposition. In addition, since it takes a long time to impregnate the electrolytic solution, problems such as variations in SEI (Solid Electrolyte Interface) formation and non-uniform electrolytic solution impregnation are likely to occur. Therefore, in order to shorten the pre-doping time, the hole diameter and the electrode thickness should be set so as to satisfy a predetermined relationship such that the movement distance of lithium ions is shortened while keeping the hole diameter of the through hole within a predetermined range. It was desired.

  Here, the proposal of patent document 3 only considers the thickness of the collector of an electrode, and is not the thickness of the whole electrode. Therefore, even if it is applied to a pre-doping type electricity storage device, it does not serve as an index for shortening the pre-doping time depending on the moving distance between the electrodes. In addition, since all of the proposals in Patent Documents 4 to 7 consider the size of the through hole and the thickness of the electrode separately, the movement distance between the electrodes determined by both the size of the through hole and the thickness of the electrode. It is not an indicator for judging long or short.

  The objective of this invention is providing the electrical storage device which can shorten pre dope time.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  That is, an electricity storage device of the present invention includes a separator, a positive electrode and a negative electrode that are stacked or wound through the separator and have a through-hole formed in a current collector, and lithium that is pre-doped in the positive electrode or the negative electrode And a lithium ion supply source for supplying ions, wherein the average value (a) of the longest diameter or longest diagonal distance of the through-hole is 1-1000 μm, the thickness of the separator, the positive electrode, and the negative electrode The value of the ratio b / a to the average value (b) of the electrode thickness defined by the sum of ½ of the thickness of the electrode is in the range of 0.08 to 530.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  That is, the average value (a) of the longest diameter or the longest diagonal distance of the through holes of the current collector is set to 1 to 1000 μm, and is defined by the sum of the thickness of the separator and half the thickness of the positive electrode and the negative electrode. Since the value of the ratio b / a with respect to the average value (b) of the electrode thickness is in the range of 0.08 to 530, the moving distance of lithium ions can be shortened. Thereby, the pre-dope time can be shortened.

It is the figure which showed typically the outline of the electrode structure at the time of applying the electrical storage device of this invention to a lithium ion capacitor. It is explanatory drawing explaining a lithium ion diffusion distance. It is a graph showing the relationship between the hole diameter of a through-hole, and lithium ion diffusion distance. (A) is a graph showing the relationship between the hole diameter of the through hole and the pre-doping time, and (b) is a graph showing the relationship between the ratio of the hole diameter of the through hole and the electrode thickness and the pre-doping time. It is a graph which shows the measurement result of pre dope time. (A) is Example 8-11, (b) is a graph which shows the tensile strength test result of Examples 4-7, 12 and 13. (A) is a graph which shows the endurance test result of Example 8 and 9, (b) is Example 10 and 11. (A) is a graph which shows the endurance test result of Example 4, 5 and 12, (b) is Example 6, 7 and 13. It is a graph which shows a resistance test result.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof is omitted as much as possible.

  FIG. 1 schematically shows an outline of an electrode configuration when the electricity storage device of the present invention is applied to a lithium ion capacitor, FIG. 2 is an explanatory diagram for explaining a lithium ion diffusion distance, and FIG. 3 is a hole diameter of a through hole. It is a graph showing the relationship between lithium ion diffusion distance. 4A is a graph showing the relationship between the hole diameter of the through hole and the pre-doping time, and FIG. 4B is a graph showing the relationship between the ratio of the hole diameter of the through hole and the electrode thickness and the pre-doping time. 3 and 4, the horizontal axis is logarithmic display.

  As shown in FIG. 1, the lithium ion capacitor 10 includes an electrode stacking unit 14 in which a plurality of positive electrodes 11 and negative electrodes 12 are alternately stacked via separators 13, and a lithium electrode 15. The positive electrodes 11 and the negative electrodes 12 are alternately stacked via separators 13. A negative electrode 12 is disposed outside the electrode laminate unit 14. Opposite to the negative electrode 11, a lithium electrode 15 as a lithium ion supply source is provided via a separator 13. Thus, the lithium ion capacitor 10 has a three-pole laminated unit structure including the positive electrode 11, the negative electrode 12, and the lithium electrode 15. Although not shown, this laminated unit is immersed in an electrolytic solution.

  In the positive electrode 11, the positive electrode active material layer 11a is provided on both surfaces of the positive electrode current collector 11b. Also in the negative electrode 12, the negative electrode active material layer 12a is provided on both surfaces of the negative electrode current collector 12b. In the lithium electrode 15, metal lithium 15a is provided on the lithium electrode current collector 15b. The positive electrode current collector 11b and the negative electrode current collector 12b are formed in a porous shape by holes penetrating the front and back. That is, a large number of through holes 11c and 12c are formed in the positive electrode current collector 11b and the negative electrode current collector 12b. Further, the positive electrode 11 is provided with a positive electrode terminal 16 which is drawn from the positive electrode current collector 11b. In the negative electrode 12, a negative electrode terminal 17 is provided by being drawn from the negative electrode current collector 12 b.

  The thus configured lithium ion capacitor 10 is put into a package (exterior material) made of a laminate film or the like, for example, as a product. Prior to making the product, lithium ions are pre-doped. That is, pre-doping is performed in a state where the exterior material is sealed in the assembly process of the lithium ion capacitor. This pre-doping is performed between the negative electrode 12 and the lithium electrode 15, and the negative electrode 12 is shipped as a product in a state where lithium ions are pre-doped. The potential of the positive electrode after the positive electrode and the negative electrode are short-circuited by lithium ion pre-doping is preferably 2 V or less, for example.

  The average hole diameter (a) of the numerous through holes 11c, 12c formed in the positive electrode current collector 11b and the negative electrode current collector 12b is 1-1000 μm, and preferably 10-1000 μm. Further, as the electrode thickness shown in FIG. 2, the average value of the total value L of the value of 1/2 of the thickness of the positive electrode 11, the thickness of the separator 13 and the value of 1/2 of the thickness of the negative electrode 12 is In the case of b, the ratio b / a to the hole diameter is 0.08 to 530. Based on the values of a and b / a, the average value (b) of the electrode thickness L is calculated as a preferable range of 80 to 530 μm. That is, assuming that the thickness of the separator 13 is 30 μm, the thickness of the positive electrode 11 and the negative electrode 12 is preferably 50 to 500 μm. The average value (b) of the electrode thickness L is more preferably in the range of 130 to 230 μm. Therefore, the value of b / a is preferably 0.13 to 23. Moreover, as for the thickness of the positive electrode 11 and the negative electrode 12, 100-200 micrometers is more preferable. In FIG. 2, a broken line is not drawn for convenience, but a negative electrode (not shown) is disposed above the positive electrode 11 and a positive electrode or lithium electrode (not illustrated) is disposed below the negative electrode 12 via a separator. Needless to say.

  The average hole diameter (a) of the through holes 11c and 12c is obtained by, for example, using an optical electron microscope or a scanning electron microscope (SEM) to randomly measure the hole diameter of the through holes at five points and obtaining the average value thereof. Can be measured. For the hole diameter of the through hole, the long diameter value is adopted when the hole is elliptical, and the longest diagonal distance value is adopted when the hole is a polygon such as a rectangle, rhombus, or slit shape. To do. For the average value (b) of the electrode thickness L, for example, in each of the positive electrode 11 and the negative electrode 12, a total of five points at the four corners and the center of the electrode cut into a rectangle (for example, 20 mm × 40 mm) are measured with a dial gauge. Find the averaged value. It is obtained by adding the thickness of the separator 13 whose average thickness is known in advance to the value of ½ of the total value of the average thicknesses of the positive electrode 11 and the negative electrode 12 thus obtained. be able to.

The range of the hole diameter, the ratio between the hole diameter and the electrode thickness, etc. was determined in this way because the following knowledge was obtained. As shown in FIG. 2, the diffusion distance in the horizontal direction during lithium ion pre-doping is the sum M of the value of ½ of the hole diameter of the through holes 11 c and 12 c and the value of ½ of the distance between the holes. It is almost equivalent. The diffusion distance in the vertical direction is approximately equal to the total value (electrode thickness) L of the value of ½ of the thickness of the positive electrode 11, the thickness of the separator 13 and the value of ½ of the thickness of the negative electrode 12. Equivalent to. That is, the lithium ion diffusion distance N can be obtained by the three-square theorem L ² + M ² = N ² . Therefore, when the value of L is constant, as shown in FIG. 3, when the lithium ion diffusion distance is plotted with the predetermined hole diameter, the lithium ion diffusion distance increases as the hole diameter increases. I understand.

  If the diffusion rate of lithium ions is the same, the diffusion time increases as the diffusion distance increases. Therefore, the diffusion distance of lithium ions can be considered by replacing it with a pre-doping time (diffusion time). That is, as shown in FIG. 4A, the larger the through-hole diameter, the longer the pre-doping time (indicated as PD time in the figure). On the other hand, as can be seen from FIG. 4 (a), it has been empirically revealed that if the pore diameter is extremely small, the active material is buried in the pores, and the pre-doping time becomes longer. Further, as described above, the independent variable for determining the lithium ion diffusion distance includes the diffusion distance of lithium ions in the vertical direction. Therefore, as shown in FIG. 4B, by plotting the ratio L / D between the hole diameter D of the through hole and the electrode thickness L, the hole diameter D of the through hole, the electrode thickness L, the pre-doping time, You can see the correlation.

  Here, the pre-doping time is preferably about 100 hours or less from the viewpoint of increasing the stability of the potential and contributing to safety such as suppression of lithium precipitation and gas generation. Therefore, when the range of the hole diameter D in which the pre-doping time is within 100 hours is seen in FIG. Moreover, when the range of L / D (range of a dashed-two dotted line) in which pre-doping time is less than 100 hours is observed in FIG.4 (b), it turns out that it is 0.08-530.

  The ratio b / a between the average hole diameter (a) of the through holes and the average value (b) of the electrode thickness L is preferably 0.13 to 23 for the following reason. is there. Electric energy storage devices for electric vehicles are required to have a high energy density, and it is highly necessary to make the electrodes thicker than conventional consumer batteries. The thickness of an electrode of a general lithium ion secondary battery or the like is about 80 μm for high output and about 160 μm for high energy for both the positive electrode and the negative electrode. The output and the energy density are in a trade-off relationship. If the electrode is too thick, the output is reduced and metal lithium is deposited. Here, since the power storage device intended by the present inventor is assumed to be used for high energy (for electric vehicles), the electrode thickness L including the thickness of the separator is less than 130 μm. This is difficult to imagine from a practical point of view. Similarly, if output characteristics and safety are taken into account, it is difficult to assume that it exceeds 230 μm.

  On the other hand, in general, an active material having a particle diameter of 10 to 20 μm is often used for a lithium ion secondary battery or the like. If a current collector having a through-hole having a pore size smaller than the particle size of the active material is used, the active material may be buried in the hole, which may hinder lithium ion diffusion during pre-doping. . For this reason, it is preferable to form a through hole having a diameter larger than that of the active material used, that is, 10 μm or larger so as not to block the hole. Further, since the current collector needs to have a hole diameter that can withstand the tensile strength during coating, the upper limit of the hole diameter of the through hole needs to be 1000 μm.

  From the above, the value of the ratio b / a between the average hole diameter (a) of the through holes and the average value (b) of the electrode thickness L is preferably 0.13 to 23.

  Thus, in the lithium ion capacitor 10, the pre-doping time can be shortened because the hole diameter and inter-hole distance of the through-holes and the electrode thickness are within appropriate ranges in relation to the pre-doping time. That is, since the potential of each electrode is stabilized quickly, it is possible to uniformly perform pre-doping. Therefore, precipitation of lithium ions and gas generation can be suppressed, which contributes to improvement of safety. Also, if the pre-doping time is short, the electrolytic solution can be impregnated quickly, so that a stable SEI (Solid Electrolyte Interface) can be formed, and the electrolytic solution can be uniformly impregnated.

  Further, from the viewpoint of tensile strength, when the positive electrode current collector 11b or the negative electrode current collector 12b is made of aluminum, the hole diameters of the through holes 11b and 12b are preferably 800 μm or less. When the positive electrode current collector 11b or the negative electrode current collector 12b is made of copper, the diameter of the through hole is not particularly limited as long as it is within the scope of the present invention. When the aperture ratio of the current collector is the same and only the hole diameter of the through hole is different, the tensile strength of the current collector is larger as the hole diameter is smaller. When a current collector having a high tensile strength is used, for example, in so-called vertical coating, the distance of the drying furnace can be increased, so that coating can be performed at a higher speed.

  When a perforated foil in which through holes are formed is used as a current collector, the strength is weaker than that of a plain foil in which through holes are not formed, and it is necessary to suppress the coating speed. In particular, when a vertical coating machine is used, the current collector may be cut by its own weight, so it is necessary to shorten the drying furnace, and high-speed coating is difficult. Moreover, the yield was liable to decrease due to the foil being cut during the process. However, by controlling the hole diameter of the through-hole formed in the current collector, the tensile strength can be improved, coating at a higher speed is possible, and the yield can be improved. .

  Further, from the viewpoint of improving the durability of the electricity storage device, the hole diameters of the through holes 11b and 12b are more preferably 500 μm or less, and particularly preferably 300 μm or less. When a current collector having a through-hole diameter of 500 μm or less is used, there is less slipping of the active material from the current collector, and the durability of the electrode is smaller than when a current collector with a larger hole diameter is used. high. The sliding down of the active material from the current collector causes a decrease in device capacity and an increase in resistance. Therefore, by preventing this, it can contribute to improving the durability of the device.

  When pre-doping is performed, a perforated foil is used for the current collector, but the active material in the vicinity of the through-hole that is not held by the current collector is brittle in strength and slips off due to vibration, etc. It was a cause of decrease and resistance increase. Also, the sliding down active material caused internal short circuit. However, by setting the diameter of the through-hole formed in the current collector to 500 μm or less, more preferably 300 μm or less, it becomes possible to control the stress when an external force is applied and suppress the sliding of the active material. can do. Thereby, it may be possible to suppress a decrease in device capacity and an increase in resistance. In particular, an electric storage device for an electric vehicle is highly effective because high durability is required.

  In addition, the hole diameters of the through holes 11b and 12b are preferably 500 μm or less and more preferably 300 μm or less from the viewpoint of directly reducing the resistance of the electricity storage device. When a perforated foil having through-holes formed in the current collector is used, the contact area with the active material tends to decrease and the resistance tends to increase. If the resistance is large, problems such as heat generation during charging, gas generation, variation in device capacity, and reduction in safety may occur. However, by setting the diameter of the through hole formed in the current collector to 500 μm or less, more preferably 300 μm or less, the resistance of the electricity storage device can be reduced even at the same aperture ratio. It is possible to suppress the heat generation and improve safety.

  Although the lithium ion capacitor 10 has a stacked cell configuration, the present invention can also be applied to a cylindrical cell configuration in which a positive electrode and a negative electrode are wound through a separator. Further, the present invention may be applied to, for example, a lithium ion secondary battery as long as it is appropriate to use a current collector with a hole, and to a device having another configuration. Also good. Further, the outermost electrode of the electrode unit may be used as a positive electrode, and the positive electrode may be pre-doped with lithium ions.

  Hereinafter, materials and components used for each element of the electricity storage device of the present invention will be described. Examples of the positive electrode current collector include aluminum and stainless steel. Examples of the negative electrode current collector include stainless steel, copper, nickel, and the like. As described above, the positive electrode current collector and the negative electrode current collector have a large number of through holes and are configured as conductive porous bodies. Moreover, the same thing can be used for a positive electrode collector and a negative electrode collector, and if it does not react with a lithium ion supply source, you may comprise by materials other than illustrated. The through-hole formed in the current collector is formed by, for example, a metal lath such as an expanded metal, a wire lath, a punching metal, an etching foil, an electrolytic etching foil, a three-dimensionally processed (3D) foil, or the like.

  The aperture ratio of the through holes in the current collector is usually 40 to 60% in both cases of the positive electrode current collector and the negative electrode current collector. Here, the aperture ratio can be defined as the area ratio of the aperture surface in the current collector. That is, strictly speaking, it is the ratio of the total area of the opening surface of the current collector to the area of the current collector metal portion. The current collector is manufactured by cutting the current collector material into pieces. The aperture ratio can be measured by verifying the manufactured current collector. For simplicity, the aperture ratio may be calculated by the ratio of the total area of the aperture surface per unit area set in the current collector material.

  The positive electrode active material layer and the negative electrode active material layer are composed of a composite material such as an active material, a binder, and, if necessary, a conductive additive. This mixture is formed into a slurry. The slurry is applied to both or one side of the current collector and dried to produce an electrode.

As the positive electrode active material, when the electric storage device is a lithium ion capacitor, forms a lithium ion, lithium ion pairs, for example BF4 @ ^-, PF6 @ ^- such, reversibly doped can material using anions such as Is done. For example, activated carbon, a conductive polymer, a polyacene-based material and the like can be given. In the case of activated carbon, for example, if a material that has been activated by an alkali metal hydroxide salt such as potassium hydroxide is used, the specific surface area is greater than that of an activated material that has not been activated. preferable. These exemplified active materials may be used alone or in combination of two or more.

  When the power storage device is a lithium ion secondary battery, the positive electrode active material includes, for example, an oxide of one or more metal elements selected from Group V elements and Group I elements of the Periodic Table Is mentioned. Examples of such metal oxides include vanadium oxide (vanadium oxide) and niobium oxide.

  Examples of the negative electrode active material include graphite, a carbon-based material, a polyacene-based material, and a lithium-based material. Examples of the carbon-based material include non-graphitizable carbon materials. Examples of the polyacene-based material include a polyacene-based organic semiconductor (PAS) that is an insoluble and infusible substrate having a polyacene-based skeleton. Examples of the lithium-based material include lithium-based metal materials such as metal lithium, for example, a lithium alloy such as a lithium-aluminum alloy. In addition, an intermetallic compound material of a metal such as tin or silicon and metal lithium, or a lithium compound such as lithium nitride is also included. These negative electrode active materials are all materials that can be reversibly doped with lithium ions.

  In the electricity storage device of the present invention, lithium ions are pre-doped into the negative electrode or the positive electrode during initial charging. Examples of the lithium ion supply source used at this time include metallic lithium and a lithium-aluminum alloy. That is, any substance that contains lithium element and can supply lithium ions can be used. In the present specification, dope means occlusion, support, adsorption, insertion, and the like. That is, it means a state in which anions, lithium ions, and the like enter the positive electrode active material and the negative electrode active material. De-doping means release, desorption and the like. That is, it means a state in which anions, lithium ions, and the like are emitted from the positive electrode active material and the negative electrode active material.

  Examples of the binder include a rubber binder and a binder resin. Examples of the rubber binder include styrene butadiene rubber (SBR) and nitrile rubber (NBR) which are diene polymers. Examples of the binder resin include a fluorine resin, a thermoplastic resin, and an acrylic resin. Examples of the fluororesin include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF). Examples of the thermoplastic resin include polypropylene and polyethylene. Examples of the acrylic resin include acrylic acid-2-ethylhexyl, methacrylic acid / acrylonitrile / ethylene glycol dimethacrylate copolymer, and the like.

  Examples of the conductive assistant include carbon black such as acetylene black and ketjen black, and conductive carbon materials such as expanded graphite, carbon fiber, and carbon nanotube. Moreover, carboxymethylcellulose (CMC) can also be used as a thickener.

  These active materials, binders, conductive assistants, thickeners, and the like can be formed into a slurry using, for example, water or a solvent such as N-methyl-2-pyrrolidone. The positive electrode active material layer and the negative electrode active material layer formed of this slurry are provided with a predetermined thickness on the current collector surface in which the through holes are formed. In providing, for example, a coating process is performed using a coating apparatus such as a die coater or a comma coater. Depending on the heat resistance of the binder, the active material layer coated on the current collector with a predetermined thickness is usually dried in a vacuum at a temperature of 100 to 200 ° C. for about 12 hours to produce an electrode.

As the electrolytic solution for immersing the laminated unit of the electricity storage device, an aprotic organic solvent can be used when the electricity storage device is a lithium ion capacitor. The aprotic organic solvent forms an aprotic organic solvent electrolyte solution. Examples of the aprotic organic solvent include ethylene carbonate, dimethyl carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride, sulfolane and the like. These may be used individually by 1 type and may use the liquid mixture which mixed 2 or more types. The electrolyte dissolved in the electrolytic solution is not particularly limited as long as it is an electrolyte that can generate lithium ions. Examples thereof include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _{2 and the} like.

When the electricity storage device is a lithium ion secondary battery, examples of the electrolytic solution include non-aqueous solvents. Examples of non-aqueous solvents include chain carbonates, cyclic carbonates, cyclic esters, nitrile compounds, acid anhydrides, amide compounds, phosphate compounds, amine compounds, and the like. More specifically, for example, ethylene carbonate, diethyl carbonate (DEC), propylene carbonate, dimethoxyethane, γ-butyrolactone, n-methylpyrrolidinone, N, N′-dimethylacetamide, acetonitrile, or propylene carbonate and dimethoxyethane Examples thereof include a mixture and a mixture of sulfolane and tetrahydrofuran. Examples of the electrolyte include lithium salts such as CF ₃ SO ₃ Li, C ₄ F ₉ SO ₈ Li, (CF ₃ SO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, LiBF ₄ , LiPF ₆ , and LiClO _4. It is done.

  As a separator, it has a large ion permeability (air permeability), a predetermined mechanical strength, durability against an electrolyte solution, a positive electrode active material, a negative electrode active material, etc. A material or the like is used. For example, paper (cellulose), rayon, glass fiber, polyethylene, polypropylene, polystyrene, polyester, polytetrafluoroethylene, polyvinylidene difluoride, polyimide, polyphenylene sulfide, polyamide, polyamideimide, polyethylene terephthalate, polybutylene terephthalate, polyether A cloth, a nonwoven fabric or a microporous body having a gap made of ether ketone or the like can be mentioned. The illustrated separator may be used alone or may be used by overlapping the same kind of separators depending on the purpose. A plurality of types of separators may be used in an overlapping manner. The thickness of the separator can be set as appropriate in consideration of the amount of electrolyte retained, the strength of the separator, etc., but the thickness of the separator is reduced in order to reduce the DC resistance of the electricity storage device and improve the energy density per volume. The thinner one is preferable. Specifically, about 15 to 40 μm is preferable.

  Hereinafter, the present invention will be further described by way of examples. In addition, this invention is not limited by these Examples. Further, in the following examples, the average value of the electrode thickness (the sum of the 1/2 value of the thickness of the positive electrode 11 and the 1/2 value of the thickness of the separator 13 and the negative electrode 12 shown in FIG. The average value of the value L) and the average hole diameter of the through holes of each current collector are measured as follows.

  [Measuring Method of Average Hole Diameter of Through Hole] Using a scanning electron microscope (SEM), the hole diameter of the through hole is randomly measured at five points, and the average value is obtained.

  [Measuring method of average value of electrode thickness] In each of the positive electrode and the negative electrode, a total of five points at the four corners and the center of the electrode cut into a rectangle (for example, 20 mm × 40 mm) are measured with a dial gauge, and an average value is obtained. . The thickness of the separator whose average thickness is known in advance is added to a value that is ½ of the total value of the average thicknesses of the positive electrode and the negative electrode thus obtained.

Example 1
[Preparation of Negative Electrode] Furfuryl alcohol, which is a raw material of furan resin charcoal, was kept at 60 ° C. for 24 hours to cure the resin to obtain a black resin. The obtained black resin was placed in a static electric furnace and heated to 1200 ° C. in 3 hours in a nitrogen atmosphere. Thereafter, the temperature was maintained for 2 hours. After cooling by cooling, the sample taken out was pulverized with a ball mill. By this pulverization, a sample of D50% (50% volume cumulative diameter) = 5.0 μm non-graphitizable carbon powder (hydrogen atom / carbon atom = 0.008) was obtained.

  Next, 100 parts by weight of the sample and a solution prepared by dissolving 10 parts by weight of polyvinylidene fluoride powder in 80 parts by weight of N-methyl-2-pyrrolidone were sufficiently mixed to obtain a negative electrode slurry. This negative electrode slurry is a copper expander having an average pore diameter of 100 μm (0.1 mm) and a thickness of 26 μm (opening ratio 50%) in which through holes are formed in the same pattern so that the distance between the holes is three times the hole diameter. The both sides of the negative electrode current collector made of metal were evenly coated with a die coater. Then, after drying and pressing, a negative electrode having an average thickness of 50 μm was obtained.

[Preparation of Positive Electrode] A composition comprising 85 parts by weight of commercially available activated carbon powder having a specific surface area of 2000 m ² / g, 5 parts by weight of acetylene black powder, 6 parts by weight of an acrylic resin binder, 4 parts by weight of carboxymethyl cellulose and 200 parts by weight of water. A positive electrode slurry was obtained by thoroughly mixing.

  Non-aqueous carbon on both sides of an aluminum expanded metal with a thickness of 38 μm (opening ratio 50%) in which through holes are formed in the same pattern so that the distance between the holes is 3 times the hole diameter. System conductive paint was coated by a spray method. Then, the positive electrode collector with the conductive layer formed was obtained by drying. The total thickness (the sum of the current collector thickness and the conductive layer thickness) was 50 μm.

  The positive electrode slurry was evenly coated on both surfaces of the positive electrode current collector with a roll coater. Then, after drying and pressing, a positive electrode having an average thickness of 110 μm (0.1 mm) was obtained.

[Preparation of electrode laminate unit] Cut 11 negative electrodes to 6.0 × 7.5 cm ² (excluding terminal welds) and 10 positive electrodes to 5.8 × 7.3 cm ² (excluding terminal welds) Cut. A commercially available cellulose / rayon mixed nonwoven fabric having an average thickness of 30 μm was used as the separator.

  That is, in Example 1, it corresponds to the average value of the total value L of the value of 1/2 of the thickness of the positive electrode 11 and the value of the separator 13 and the value of 1/2 of the thickness of the negative electrode 12 shown in FIG. The average value of the electrode thickness is 110 μm, and the ratio b / a of the average value of the average hole diameter (a) of the through holes and the average value of the electrode thickness (b) is 1.1.

  The terminal welded portions of the positive electrode current collector and the negative electrode current collector were arranged on the opposite sides through the separator, and the positive electrode and the negative electrode were alternately laminated. In the lamination, the outermost part of the electrode was made to be the negative electrode. In addition, separators were arranged at the uppermost part and the lowermost part, and four sides were taped. Further, the terminal welded portion (10 sheets) of the positive electrode current collector and the terminal welded portion (11 sheets) of the negative electrode current collector were respectively made of an aluminum positive electrode terminal and a copper negative electrode having a width of 50 mm, a length of 50 mm, and a thickness of 0.2 mm. Ultrasonic welded to the terminal. In this way, an electrode laminate unit was obtained.

  [Preparation of Lithium Electrode] A lithium electrode in which a metal lithium foil was pressure-bonded to a stainless steel net having a thickness of 80 μm was used. This lithium electrode was disposed so as to completely face the outermost negative electrode. That is, one lithium electrode was disposed outside the electrode laminate unit, and a lithium electrode for potential monitoring was disposed outside the lithium electrode, to obtain a three-electrode laminate unit. The terminal welded portion of the lithium electrode current collector was resistance welded to the negative electrode terminal welded portion.

  [Preparation of Cell and Impregnation with Electrolyte] A three-electrode laminate unit was placed inside a 3.5 mm laminate film deep-drawn in accordance with the shape of the electrode laminate unit. Also, the three sides of the lower side and side sides of the laminate film were heat-sealed.

Subsequently, a funnel was inserted into the remaining side where heat fusion was not performed, and 15 g of a propylene carbonate solution as an electrolytic solution was injected with a spoid. This propylene carbonate solution was prepared by dissolving LiPF ₆ to a concentration of 1 mol / L with respect to propylene carbonate. Thereafter, the remaining side was fused under reduced pressure to assemble a film type cell as an electricity storage device of the present invention. In addition, the metallic lithium arrange | positioned in a cell is equivalent to 550 mAh / g per negative electrode active material weight.

(Example 2)
A film-type cell was assembled in the same manner as in Example 1 except that the average hole diameter of the through holes in the current collector of the positive electrode and the negative electrode was 250 μm (0.25 mm). Here, in Example 2, the ratio b / a between the average hole diameter (a) of the through holes and the average value (b) of the electrode thickness is 0.44.

(Example 3)
A film type cell was assembled in the same manner as in Example 1 except that the average hole diameter of the through holes in the current collector for the positive electrode and the negative electrode was 500 μm (0.5 mm). Here, in Example 3, the ratio b / a between the average hole diameter (a) of the through holes and the average value (b) of the electrode thickness is 0.22.

(Comparative Example 1)
A film type cell was assembled in the same manner as in Example 1 except that the average pore diameter of the through holes in the positive and negative electrode current collectors was 0.1 μm. Here, in Comparative Example 1, the ratio b / a between the average hole diameter (a) of the through holes and the average value (b) of the electrode thickness is 1100.

(Comparative Example 2)
A film-type cell was assembled in the same manner as in Example 1 except that the average hole diameter of the through holes in the current collector of the positive electrode and the negative electrode was 2000 μm. Here, in Comparative Example 2, the ratio b / a between the average hole diameter (a) of the through holes and the average value (b) of the thickness of the electrodes is 0.055.

  [Measurement of pre-doping time] The film type cells obtained in Examples 1 to 3 were measured as the pre-doping time from the time the metal lithium was impregnated until the metallic lithium completely disappeared. The results are shown in FIG.

  From the results of FIG. 5, it was found that in all of Examples 1 to 3, the average hole diameter of the through holes and the thickness of the electrodes were within the preferred ranges of the present invention, so that the pre-doping time could be shortened to within 50 hours. Further, from Examples 1 to 3 and Comparative Example 2, it was confirmed that the pre-doping time (indicated as PD time in the figure) becomes longer as the through-hole diameter increases. Further, it was confirmed from Comparative Example 1 that the pre-doping time becomes longer when the diameter of the through hole is extremely small.

Example 4
A film type cell was assembled in the same manner as in Example 2, except that the thickness of the negative electrode current collector was 10 μm (the average thickness of the negative electrode was 40 μm, and Examples 5 and 12 were also the same). Note that the thickness of the electrode as a whole may be the same even if the current collector is different, because the conditions at the time of active material coating are arbitrarily changed (the followings) The same applies to the example).

(Example 5)
A film type cell was assembled in the same manner as in Example 3 except that the thickness of the negative electrode current collector was 10 μm.

(Example 6)
A film type cell was assembled in the same manner as in Example 2, except that the thickness of the negative electrode current collector was 20 μm (the average thickness of the negative electrode was 50 μm, and the same applies to Examples 7 and 13).

(Example 7)
A film type cell was assembled in the same manner as in Example 3 except that the thickness of the negative electrode current collector was 20 μm.

(Example 8)
In Example 1, a positive electrode current collector was formed with through holes having an average pore diameter of 300 μm (0.3 mm) and a thickness of 15 μm (the average thickness of the positive electrode was 110 μm, the same applies to Example 9). A film type cell was assembled in the same manner except that it was used.

Example 9
A film-type cell was assembled in the same manner as in Example 1 except that through-holes having an average pore diameter of 500 μm (0.5 mm) were formed in the positive electrode current collector and the thickness was 15 μm.

(Example 10)
In Example 1, through-holes having an average pore diameter of 300 μm (0.3 mm) were formed in the positive electrode current collector, and the thickness was 30 μm (the average thickness of the positive electrode was 120 μm, the same applies to Example 11). A film type cell was assembled in the same manner except that it was used.

(Example 11)
A film-type cell was assembled in the same manner as in Example 1 except that through-holes having an average pore diameter of 500 μm (0.5 mm) were formed in the positive electrode current collector and the thickness was 30 μm.

(Example 12)
A film type cell was assembled in the same manner as in Example 1 except that the thickness of the negative electrode current collector was changed to 10 μm.

(Example 13)
A film type cell was assembled in the same manner as in Example 1 except that the thickness of the negative electrode current collector was 20 μm.

  [Tensile Strength Test] The film type cells of Examples 4 to 13 were examined for tensile strength in the flow (MD) direction and the vertical (TD) direction according to JIS Z2241. The results are shown in the graph of FIG. 6A for Examples 8 to 11, and the graph of FIG. 6B for Examples 4 to 7, 12 and 13.

  From the results shown in FIG. 6A, the strength is sufficiently higher than the minimum tensile strength (MD direction: 2.7 N / 10 mm, TD direction: 2.7 N / 10 mm) that allows the current collector to be applied to the coating machine. I found it. Further, it was found that the smaller the average hole diameter of the through-holes, the higher the tensile strength, and the value shows a linear tendency on the graph. From this, in the graphs of FIGS. 6 (a) and 6 (b), the longest slope of the data obtained with the same current collector thickness is extended until the above-mentioned minimum tensile strength is reached. The value of the average hole diameter corresponding to the case is estimated to be the upper limit of the hole diameter of the through hole that can be manufactured by the coating machine. Specifically, 800 μm or less is suitable for a positive electrode current collector using aluminum, and 1200 μm or less for a negative electrode current collector using copper, that is, a range defined by the present invention (1-1000 μm). It was speculated that there should be.

  [Durability Test] The film type cells of Examples 4 to 13 were acceleratedly tested using an ultrasonic cleaner (Tokyo Ultrasonic Giken Co., Ltd., ultrasonic cleaner UC-0310). Specifically, the ultrasonic cleaner was continuously applied for 7.5 minutes, and after 2.5, 5 and 7.5 minutes, the positive electrodes of Examples 4 to 7, 12 and For No. 13, the remaining amount (%) of the negative electrode relative to the start of the test of the active material applied to the current collector was visually determined, and the value was used as an index of durability. The results are shown in the graph of FIG. 7 (a) or (b) for Examples 8 to 11, and the graph of FIG. 8 (a) or (b) for Examples 4 to 7, 12 and 13, respectively.

  From the results of FIGS. 7 and 8, it was found that the current collector having a smaller through-hole has a larger amount of active material and is excellent in durability. Further, if the remaining amount is 90% or more for the positive electrode and the remaining amount is 40% or more for the negative electrode, the average hole diameter of the through holes is 500 μm (0. 5 mm) or less was found to be preferable. Furthermore, it was found that the average hole diameter of the through holes is 300 μm (0.3 mm) or less, since the durability is drastically improved, which is more preferable.

  [Resistance Test] The direct current internal resistance (DC-IR) of the film type cells of Examples 4 to 7, 12 and 13 was measured. The results are shown in FIG.

  From the results of FIG. 9, it was found that the smaller the through-hole, the lower the internal resistance. Further, when the case where the internal resistance is 0.18Ω or less is regarded as a good range of the internal resistance value, it has been found that the average hole diameter of the through holes is preferably 500 μm (0.5 mm) or less. Furthermore, it was found that the average hole diameter of the through holes is 300 μm (0.3 mm) or less, since the resistance is drastically reduced, which is more preferable.

  The present invention can be effectively used in the field of power storage devices.

DESCRIPTION OF SYMBOLS 10 Lithium ion capacitor 11 Positive electrode 11a Positive electrode active material 11b Positive electrode collector 11c Through-hole 12 Negative electrode 12a Negative electrode active material 12b Negative electrode collector 12c Through-hole 13 Separator 14 Electrode laminated unit 15 Lithium electrode 15a Metal lithium 15b Lithium electrode current collector 16 Positive electrode terminal 17 Negative electrode terminal L Total value of the thickness of the positive electrode, the thickness of the separator and the value of 1/2 of the thickness of the negative electrode (electrode thickness)
M Total of the value of ½ of the hole diameter of the through hole and the value of ½ of the distance between holes

Claims (5)

A separator, a positive electrode and a negative electrode that are stacked or wound through the separator and have a through-hole formed in a current collector, and a lithium ion supply source that supplies lithium ions that are pre-doped in the positive electrode or the negative electrode An electricity storage device comprising:
The average value (a) of the longest diameter or the longest diagonal distance of the through-hole is 1-1000 μm, and is defined by the sum of the thickness of the separator and the half value of the positive electrode and the negative electrode The electrical storage device, wherein the ratio b / a with respect to the average thickness (b) is in the range of 0.08 to 530. The electricity storage device according to claim 1,
A power storage device having a value of b / a in a range of 0.13 to 23. The electricity storage device according to claim 1 or 2,
The average value (a) of the longest diameter or longest diagonal distance of the through-hole is 800 μm or less when the current collector is made of aluminum, and 1000 μm or less when the current collector is made of copper. An electricity storage device. In the electrical storage device of any one of Claims 1-3,
The average value (a) of the longest diameter or longest diagonal distance of the through-hole is 500 μm or less. In the electrical storage device of any one of Claims 1-4,
The electrical storage device, wherein an aperture ratio of the through hole is 40 to 60%.

Images