JP4931239B2 - Power storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power storage device small in characteristic degradation by preventing free matter of small pieces of lithium metal from flowing out from the vicinity of a lithium metal plate in a cell, and high in safety. <P>SOLUTION: Both surfaces of the lithium metal plate is covered with two separators 4, and the two separators 4 are jointed to each other by a fused junction part 7 formed in the circumference of the lithium metal plate 8 to seal the lithium metal plate. The power storage element 1 is composed by stacking the sealed lithium metal plate, and a basic cell formed by facing, through the separators 4, a positive electrode 2 formed of a polarizing electrode to negative electrodes 3 each formed of an electrode with lithium ions previously doped therein by being brought into contact with lithium. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an electricity storage device using a hybrid capacitor as an alternative or secondary power supply source for a secondary battery.

  Electric double layer capacitors can be charged quickly and can be discharged with a large current, and the characteristics will not deteriorate even after repeated charging and discharging 10,000 times or more. It has features not found in secondary batteries such as batteries. For this reason, in recent years, there is an increasing expectation for an electric double layer capacitor as an alternative to the secondary battery or as an auxiliary power supply source.

  In an electric double layer capacitor, a pair of polarizable electrodes each having a polarizable electrode layer mainly composed of activated carbon are disposed to face each other via a separator to constitute a capacitor element, and the polarizable electrode layer is impregnated with an electrolytic solution. Yes. Then, an electric double layer is formed at the interface between each polarizable electrode layer and the electrolytic solution. When a voltage is applied to the electric double layer capacitor, electric charges are accumulated in the capacitance of the electric double layer.

  Recently, an electricity storage device using a hybrid capacitor using a polarizable electrode used for an electric double layer capacitor as a positive electrode and a carbon material capable of inserting and extracting lithium ions as a negative electrode has been proposed. In the electricity storage element that is a component of this electricity storage device, it becomes possible to increase the voltage of the electricity storage element (potential difference between the positive electrode and the negative electrode) by using a carbon material with a low lithium ion storage / desorption potential for the negative electrode, A power storage element with high withstand voltage and high energy density can be provided. In addition, by using a polarizable electrode used in an electric double layer capacitor for the positive electrode, charges are accumulated in the electric double layer formed at the interface between the polarizable electrode layer and the electrolytic solution. Unlike a lithium ion secondary battery, the positive electrode active material itself does not involve a chemical reaction that occludes and desorbs lithium ions, so that an electricity storage device having an excellent charge / discharge cycle can be provided.

  For example, in Patent Document 1, a polarizable electrode made of activated carbon is used as a positive electrode, and lithium is used as a carbon material that can be occluded / released in a negative electrode active material in a state where lithium is ionized as a negative electrode active material. A hybrid electric double layer capacitor using a carbonaceous material occluded by the method has been proposed. FIG. 3 is an explanatory diagram of a power storage element of a conventional hybrid capacitor. As shown in FIG. 3, in the storage element 101, a polarizable electrode is used for the positive electrode 102, an electrode capable of reversibly carrying lithium is used for the negative electrode 103, and a separator 104 is disposed between the positive electrode 102 and the negative electrode 103. A basic cell is configured, and a lithium metal plate 108 and a separator 104 are laminated on the basic cell. These members are each impregnated with an electrolyte solution 106 of a non-aqueous solution containing a lithium salt.

  In Patent Document 2 and Patent Document 3, when assembling the electricity storage device 101 as shown in FIG. 3, a lithium metal is supported on the lithium metal plate 108 and an electrolyte is injected to A power storage device 101 has been proposed in which the negative electrode 103 is brought into electrochemical contact and lithium ions are supported on the negative electrode active material via an electrolytic solution.

Japanese Patent Laid-Open No. 8-1007048 WO00 / 07255 WO2003 / 003395 publication

  The power storage device 101 has a configuration in which a predetermined amount of lithium ions is doped into the carbon material of the negative electrode 103 using a lithium metal plate 108 in which a lithium metal foil is bonded to a copper foil or a copper expanded metal. In the dope process, lithium metal emits electrons and is ionized to dissolve in the electrolytic solution, while the carbon material of the negative electrode undergoes a reaction that takes in lithium ions and electrons in the electrolytic solution to form a carbon intercalation compound. Since the reaction proceeds as long as the lithium metal is supported on the lithium metal plate, the doping amount of the negative electrode carbon material can be controlled by defining the weight of the lithium metal foil.

  However, the consumption of lithium in the doping process is not uniform due to variations in the thickness of the lithium metal plate and the difference in contact resistance. Depending on the lithium metal loading state and surface state (for example, the presence of an oxidized portion) Due to the difference in speed, some of the lithium metal supported on the lithium metal plate may become small pieces and be released. When such a free substance flows out from the vicinity of the lithium metal plate in the cell and comes into contact with the aluminum of the positive electrode current collector, a local battery is formed between the lithium and the aluminum, resulting in corrosion of the aluminum, increasing resistance and reliability. Causes a drop. Furthermore, since the liberated lithium metal pieces have electrical conductivity, there is a possibility that a short circuit may be caused in some cases, resulting in a problem that the safety of the cell is lowered.

  The present invention has been made in view of such a problem, and prevents a lithium metal small piece from flowing out from the vicinity of the lithium metal plate in the cell, has a small characteristic deterioration, and has a high safety. The purpose is to provide.

The present invention comprises a basic cell in which a positive electrode made of a polarizable electrode and a negative electrode made of an electrode preliminarily doped with lithium ions are brought into contact with lithium metal via a separator, and the basic cell and the lithium metal plate It was laminated, in the energy storage device using a solution of a non-aqueous, containing a lithium salt as an electrolytic solution, the lithium metal plate is rectangular, 2 both surfaces of the lithium metal plate carrying the lithium metal other with sandwiched by sheets of separator, the other two separators are joined by fusion bonding portion formed on the outer periphery of the four sides of the lithium metal plate, wherein the lithium metal plate by the other two separators is sealed It is an electricity storage device characterized by being stopped.

  The electricity storage element in the electricity storage device of the present invention is generated from the lithium metal plate by covering both surfaces of the lithium metal plate with a separator and fusing the periphery of the lithium metal plate to form a fusion bonding portion in the separator. It is possible to prevent the lithium metal small pieces from flowing out from the vicinity of the lithium metal plate in the cell.

  Furthermore, by suppressing the outflow of the lithium metal free substance by the fusion bonded portion, corrosion of the positive electrode current collector aluminum due to contact with the conductive lithium metal free object can be prevented, and as a result, the electricity storage device It is possible to prevent deterioration of characteristics and deterioration of reliability. Moreover, the short circuit by metallic lithium can be suppressed by preventing the outflow of the lithium metal free substance.

  Therefore, in the step of doping lithium ions into the negative electrode, even if lithium metal floats are generated due to the difference in the consumption rate of lithium metal, the lithium metal plate is completely sealed by the fusion bonded portion of the separator. Thus, the outflow of free lithium metal can be eliminated.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram of a power storage element according to an embodiment of the present invention. As shown in FIG. 1, the storage element 1 uses a polarizable electrode as the positive electrode 2 and an electrode capable of reversibly carrying lithium in the negative electrode 3, and a separator 4 is disposed between the positive electrode 2 and the negative electrode 3. A lithium metal plate 8 (not shown) is covered with another separator 4 and laminated. These members are each impregnated with an electrolyte solution 6 of a non-aqueous solution containing a lithium salt. The separator 4 covering the lithium metal plate 8 is formed into a bag shape by a fusion bonded portion 7 in which the periphery of the lithium metal plate 8 is fused and bonded.

  FIG. 2 is a top view of a lithium metal plate covered with a separator. In FIG. 2, a lithium metal plate 8 made of a current collector having an extended external connection electrode portion is disposed on the back surface of the frontmost separator 4, and another separator 4 is disposed on the back surface thereof. The outer peripheral portions of the two separators 4 that are the outer peripheral portions of the lithium metal plate 8 are joined by the fusion joint portion 7. The lithium metal plate 8 is sealed with the separator 4 by sandwiching the lithium metal plate 8 between the two separators 4 and providing the weld joint 7 on the outer periphery.

  In the present embodiment, the storage element 1 having such a configuration is assembled, and when the lithium metal is supported on the lithium metal plate 8 and an electrolytic solution is added, the negative electrode 3 and the lithium metal plate 8 are interposed via the electrolytic solution. Are in electrochemical contact, the lithium metal of the lithium metal plate 8 is dissolved, and lithium metal ions are doped into the negative electrode active material of the negative electrode 3. The main body of the lithium metal is carried at a location sealed by the separator 4 of the lithium metal plate 8.

  As described above, since the lithium metal plate 8 is sealed by the fusion-bonding portion 7 of the separator, the lithium metal free matter is melted even when lithium metal free matter is generated during lithium doping to the negative electrode 3. Outflow from the space provided by the bonding joint 7 to the outside is prevented. That is, it is possible to prevent the liberated lithium metal generated from the lithium metal plate 8 from coming into contact with the current collectors of other electrodes existing outside the separator 4.

Here, the power storage element of this embodiment will be specifically described. The positive electrode 2 is obtained by integrating a current collector 5 made of aluminum foil or nickel foil and an active material mainly composed of a carbon material. The current collector 5 has an extended external connection electrode portion for connecting to an external electrode. The positive electrode 2 is manufactured by further adding a conductive agent and a binder. Carbon materials include plant materials such as wood, sawdust, coconut husk and pulp waste, coal, heavy petroleum oil, or coal-based and petroleum-based pitches obtained by pyrolyzing them, petroleum coke, carbon aerogel, tar Various raw materials such as fossil fuel-based materials such as pitch, synthetic polymer materials such as phenol resin, polyvinyl chloride resin, and polyvinylidene chloride are used. After carbonizing these materials, they are activated by gas activation method or chemical activation method. the specific surface area of 700~3000m ² / g, in particular carbon materials 1000 to 2000 ² / g are preferred.

  As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, and thermally expanded graphite carbon fiber are preferable, and it is more preferable to add about 5 to 30% by weight. In addition, as the binder, polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin copolymer cross-linked polymer, polyvinyl alcohol, polybutadiene rubber, styrene-butadiene rubber, and the like are used. In particular, polytetrafluoroethylene is preferable from the viewpoints of heat resistance, chemical resistance, and sheet strength.

The negative electrode 3 is obtained by integrating a current collector 5 made of copper foil or nickel foil and an active material. The current collector 5 has an extended external connection electrode portion for connecting to an external electrode. The negative electrode 3 is manufactured by further adding a conductive agent and a binder. As the active material, it is possible to use carbon-based materials such as graphite and amorphous carbon, Sn-based composite oxides such as SnO _{2 and the} like that can be doped and dedoped with lithium ions. As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, and thermally expanded graphite carbon fiber are preferable, and it is more preferable to add about 5 to 30% by weight. In addition, as the binder, polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin copolymer cross-linked polymer, polyvinyl alcohol, polybutadiene rubber, styrene-butadiene rubber, and the like are used. In particular, polyvinylidene fluoride is preferable from the viewpoints of heat resistance, chemical resistance, and sheet strength.

  The separator is preferably made of a material having a thin thickness of 10 to 50 μm and high electronic insulation and ion permeability, and is not particularly limited. For example, a nonwoven fabric such as polyethylene or polypropylene, or viscose rayon or natural cellulose. Papermaking or the like is preferably used.

  The lithium metal plate 8 has a structure in which lithium metal is laminated and integrated on a copper current collector 5. This lithium metal is dissolved when doping the negative electrode with lithium. The copper current collector 5 may be a plain foil or may be an embossed or expanded shape having a through hole. Moreover, the lithium metal plate 8 is covered with the separator 4, and the outer peripheral portion of the separator 4 which is the outer peripheral portion of the lithium metal plate 8 is formed by bonding at the fusion bonding portion 7 and is formed into a bag shape. Thus, the lithium metal plate 8 is accommodated in the bag-like separator 4 and the lithium metal plate 8 is sealed.

  The above-mentioned fusion bonding part 7 can be formed by fusion means such as heat fusion, ultrasonic fusion, and high frequency fusion of thermoplastic resin. In particular, in the case of a separator made of a thermoplastic microporous film such as polyethylene or polypropylene, it is possible to easily form a fusion bonded portion when the separators are fused. Even when a non-thermoplastic non-woven fabric separator such as cellulose is used, the thermoplastic resin flows between the fibers of the cellulose material by fusing the thermoplastic resin such as polyfloprene, polyethylene and ionomer between the separators. Then, the fusion bonded portion 7 can be formed by cooling.

  The preferred embodiments of the electricity storage device according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea disclosed in the present application, and these are naturally within the technical scope of the present invention. Understood.

  Next, a specific example is given and the electrical storage element of this invention is demonstrated in more detail.

Example 1
Polyvinylidene fluoride (mixed powder: binder = 9: 1) in which KOH activated charcoal having a specific surface area of 2500 m ² / g and carbon black were mixed at a weight ratio of 8: 1 and dissolved in N-methylpyrrolidone as a binder. And kneaded to obtain a slurry. Next, the slurry was uniformly coated on both sides of the etched aluminum foil having a thickness of 30 μm. Then, the positive electrode sheet with a coating thickness of 80 μm was obtained by drying and rolling. For the positive electrode, two of the electrodes obtained above were cut out so that the portion where the active material was applied was 23 mm × 32 mm 2.

  Next, an amorphous carbon material and carbon black are mixed at a weight ratio of 90: 5, and polyvinylidene fluoride (mixed powder: binder = 95: 5) dissolved in N-methylpyrrolidone as a binder is added to this mixed powder and kneaded. A slurry was obtained. Next, the slurry was uniformly coated on both sides of a copper foil having a thickness of 15 μm. Then, the negative electrode sheet with a coating thickness of 20 μm was obtained by drying and rolling. As for the negative electrode, three of the electrodes obtained above were cut out so that the portion where the active material was applied was 24 mm × 33 mm.

  Next, a lithium metal foil having a thickness of 40 μm was cut out to 20 mm × 30 mm (doping ability: 49 mAh), and this lithium foil was pressure-bonded to a copper foil having a thickness of 15 μm and 20 mm × 30 mm to obtain a lithium metal plate. This lithium metal plate was sandwiched between two cellulose separators, and an ionomer, which is a thermoplastic resin, was placed around the lithium metal plate. A portion where the ionomer is disposed is heat-sealed from above the separator, so that a fusion bonding portion of a thermoplastic resin is provided on the outer peripheral portion of the lithium electrode.

  The positive electrode and the negative electrode produced as described above were alternately laminated so that the outermost electrode plate would be a negative electrode and a separator was placed outside the negative electrode (separator / negative electrode / separator The negative electrode, the positive electrode, and the separator were stacked in the order of / positive electrode unit / separator / negative electrode / separator / positive electrode unit / separator / negative electrode / separator). Note that the current collectors of the positive electrode, the negative electrode, and the lithium metal plate are cut out so as to have external electrode joints extending at the time of manufacture. Furthermore, a lithium metal plate covered with a separator is disposed on the outermost layer of the laminate, and the negative electrode current collector laminated with the current collector of the lithium metal plate protrudes outside the exterior film and the exterior film. The negative external electrodes were ultrasonically welded together. Similarly, the positive electrode external electrode joint and the positive electrode protruding outside the exterior film (not shown) were ultrasonically welded together.

  The electrode laminate thus obtained was housed in an exterior film, and an electrolytic solution was injected. As the electrolytic solution, an electrolytic solution in which LiPF6 was dissolved to a concentration of 1 mol / L in a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used. After injecting the electrolyte, the outer package was sealed in a vacuum atmosphere, thereby obtaining an electricity storage device.

(Example 2)
An electricity storage device was produced in the same manner as in Example 1 except that a polyethylene separator was used.

(Example 3)
A power storage device was produced in the same manner as in Example 1 except that a polyethylene separator was used and the separator was thermally fused without using a thermoplastic resin to provide a fusion bonded part.

(Comparative example)
In Example 1, an electric storage device was produced in the same manner as in Example 1 except that the electrode of the lithium metal plate was sandwiched between two cellulose separators and no fusion bonding part was provided.

  As described above, power storage devices manufactured by the methods of Examples 1 to 3 and the comparative example were obtained. The produced electricity storage device was measured for ESR (equivalent series resistance) in a thermostat set at 25 ° C. Here, ESR was obtained by using a sine wave oscillator with an alternating current of 1 kHz, passing an alternating current of 10 mA through the electric storage device, and measuring and calculating the voltage across the electric storage device. Next, constant current and constant voltage charging was performed for 1 hour at a maximum current of 10 mA and a maximum voltage of 4.0 V, the discharge current was 5 mA, and discharge was performed at a constant current until the voltage of the storage element showed 2 V, and the initial current capacity was confirmed. .

  After confirming the initial characteristics, the electricity storage device was moved to a high-temperature bath at 60 ° C., and a voltage application test for 1000 hours was performed at an applied voltage of 4.0V. After the application test was completed, the sample was left for 3 hours in a high-temperature bath set at 25 ° C., and the characteristics of the electricity storage device were confirmed under the same measurement conditions as those for the initial characteristics.

  Table 1 shows the initial characteristics and average values of ESR, capacitance and self-discharge characteristics before and after voltage application of the electric double layer capacitors produced by the methods of Examples 1 to 3 and the comparative example. The ESR, capacitance, and self-discharge characteristics are average values of 100 manufactured samples.

  From Table 1, when the ESR and discharge current capacity of Examples 1 to 3 and the comparative example are compared, the initial values are equivalent. However, in the comparative example, it was confirmed that a short circuit occurred due to liberation of lithium metal fine particles. In this embodiment, both sides of the lithium metal plate are covered with the separator, and the separator is joined by a fusion joint formed around the lithium metal plate, and the lithium metal plate is sealed with the separator. Short-circuiting due to the release of metal fine particles could be suppressed.

  Further, in the comparative example after the voltage test, out of 100 samples, two ESRs exceeded 50 mΩ. As a result of disassembling and analyzing these interiors, the positive electrode current collector was corroded by contact with lithium metal liberation, and this is considered to have deteriorated the electrical characteristics. In Examples 1 to 3, no significant ESR degradation was confirmed, and it was considered that good results were obtained even when a voltage application test for 1000 hours was performed at 60 ° C. and an applied voltage of 4.0 V.

  From the above results, the outer periphery of the two separator sheets is fused and processed into a bag shape, and the lithium metal plate is stored in the bag-shaped separator, so that short-circuit defects can be suppressed and reliability is further improved. It was found that an electricity storage device excellent in the production can be manufactured. At this time, it was found that an inexpensive material such as natural cellulose can be used as a material for the separator sheet. It has been found that good results can be obtained for both fusion of the outer peripheral portion and the thermoplastic resin ionomer on the outer peripheral portion, or using a thermoplastic resin sheet.

  In this example, cellulose and polyethylene separators were used, but the present invention can be applied to porous separators other than resins and cellulose materials, and is not limited thereto.

Explanatory drawing of the electrical storage element in embodiment of this invention. The top view which coat | covered the lithium metal plate with the separator. Explanatory drawing of the electrical storage element of the conventional hybrid capacitor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Electric storage element 2,102 Positive electrode 3,103 Negative electrode 4,104 Separator 5,105 Current collector 6,106 Electrolyte 7 Fusion joint part 8,108 Lithium metal plate

Claims (1)

A basic cell is configured by facing a positive electrode made of a polarizable electrode through a separator and a negative electrode made of an electrode pre-doped with lithium ions in contact with lithium metal, and the basic cell and the lithium metal plate are laminated, In an electricity storage device using a non-aqueous solution containing a lithium salt as an electrolytic solution, the lithium metal plate is rectangular, and both surfaces of the lithium metal plate carrying the lithium metal are separated by two other separators. In addition, the other two separators were joined by the fusion joints formed on the outer periphery of the four sides of the lithium metal plate, and the lithium metal plate was sealed by the other two separators. An electricity storage device characterized by the above.

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