JP2012028366A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device having charging/discharging characteristics of no voltage changes versus time.SOLUTION: The power storage device includes a unit formed by alternately stacking positive electrodes 9 and negative electrodes 10 through separators 3. Each of the positive electrodes has a positive electrode active material layer 1 and a positive electrode current collector 4. Each of the negative electrodes 10 has a negative electrode active material layer 2 and a negative electrode current collector 5. Active carbon and transition metal oxide are combined with the positive electrode active material layer 1.

Description

  The present invention relates to an electricity storage device such as a lithium ion capacitor.

  Energy storage devices are used as energy sources for driving motors such as electric vehicles, or as key devices for energy regeneration systems in consideration of oil reserves and environmental issues such as global warming. Application to various new uses such as application to photovoltaic power generation is being studied, and it is a highly anticipated device as a next-generation device.

  In recent years, there has been a demand for higher energy density and lower resistance for power storage devices in applications for energy sources and energy regeneration.

  A lithium ion secondary battery is composed of a positive electrode mainly composed of a lithium-containing transition metal oxide, a negative electrode mainly composed of a carbon material capable of inserting and extracting lithium ions, and an organic electrolyte containing a lithium salt. ing. When the lithium ion secondary battery is charged, lithium ions are desorbed from the positive electrode and occluded in the carbon material of the negative electrode. Conversely, when discharged, lithium ions are desorbed from the negative electrode and occluded in the metal oxide of the positive electrode. Lithium ion secondary batteries have the characteristics of higher voltage and higher capacity than electric double layer capacitors, and the characteristics of charging and discharging at constant current are around the potential inherent to metal oxides over time. Although there is a portion where the voltage does not change, the internal resistance is high, and it is difficult to reduce the resistance.

  On the other hand, electric double layer capacitors are generally classified into aqueous electrolyte type and non-aqueous electrolyte type depending on the type of electrolyte used, but the withstand voltage of a single electric double layer capacitor is aqueous electrolyte. In the case of the type, it is about 1.2 V, and in the case of the non-aqueous electrolyte type, it is about 2.7 V. The characteristics of charging and discharging at a constant current have characteristics that are almost linear with respect to time. In order to increase the energy capacity that can be stored in the electric double layer capacitor, it is a problem to further increase the capacity due to the positive electrode.

  In order to reduce the resistance of a lithium ion secondary battery and increase the capacity of an electric double layer capacitor, it is necessary to improve the technology, energy density, and output density of the negative electrode containing lithium (doping).

  For example, Patent Document 1 discloses that a positive electrode current collector and a negative electrode current collector each have a hole penetrating the front and back surfaces, the negative electrode active material can reversibly carry lithium, and the negative electrode-derived lithium is a negative electrode. Alternatively, an organic electrolyte battery is described in which the electrode is moved and supported between the front and back surfaces of the electrode by electrochemical contact with lithium arranged opposite to the positive electrode, and the opposite area of the lithium is 40% or less of the negative electrode area. .

  Patent Document 2 describes a power storage device that can improve energy density and output density by including positive electrodes that are arranged so that different types of positive electrodes sandwich the negative electrode.

Japanese Patent No. 3485935 JP 2009-26480 A

  Lithium ion capacitors use activated carbon for the positive electrode and a carbon material that can occlude and desorb lithium ions for the negative electrode. Since the negative electrode is subjected to occlusion and desorption reactions in the negative electrode during charge and discharge, the potential difference between the two electrodes actually generated in the capacitor is closer to the case of using lithium metal that changes at a lower value by the negative electrode. Therefore, the withstand voltage can be further increased as compared with the conventional electric double layer capacitor using activated carbon for the positive electrode and the negative electrode, and the amount of energy that can be stored is greatly increased compared with the electric double layer capacitor (high Energy) and low resistance compared to lithium ion secondary batteries.

  However, lithium-ion capacitors have constant current charging and discharging characteristics that vary in voltage almost linearly with time, and less energy can be stored than lithium-ion secondary batteries. .

  The above charging and discharging characteristics are almost the same as those of the electric double layer capacitor. These characteristics of the lithium ion secondary battery have a portion where the voltage hardly changes with time.

  And if it has a some positive electrode layer like patent document 2, a manufacturing cost will become high by management etc. becoming complicated by a manufacturing process. Further, the product life may depend on either positive electrode layer.

  Therefore, it is easy to manufacture at a low cost by giving the lithium ion capacitor the characteristics of charge and discharge that do not change voltage with time like a lithium ion secondary battery and increasing the amount of energy that can be stored. A power storage device that can be used is needed.

  That is, the technical problem of the present invention is to provide a power storage device that has charging and discharging characteristics in which the voltage hardly changes with time and increases the amount of energy that can be stored.

  The electricity storage device of the present invention includes a positive electrode active material layer having activated carbon and a transition metal oxide, thereby having charge and discharge characteristics in which the voltage hardly changes with time, and increasing the amount of energy that can be stored. It has been found that it can be. That is, the electricity storage device of the present invention includes a non-aqueous electrolyte solution containing lithium ions, a positive electrode in which a positive electrode active material layer having activated carbon and a transition metal oxide is formed on a positive electrode current collector, and a negative electrode current collector. And a negative electrode on which a negative electrode active material layer capable of reversibly doping lithium ions is formed, the positive electrode and the negative electrode are alternately stacked or wound through a separator, and a lithium supply source is opposed to the negative electrode. It is characterized by having arranged.

  Furthermore, in the electricity storage device of the present invention, the transition metal oxide may be made of manganese oxide.

  Furthermore, in the electricity storage device of the present invention, it is preferable that a mixing ratio of the activated carbon and the transition metal oxide in the positive electrode active material layer is 15% to 75% in terms of a mass ratio of the transition metal oxide.

  As a result, it is possible to have charge and discharge characteristics in which the voltage hardly changes with time at a potential unique to a transition metal oxide that has a larger amount of energy that can be stored than activated carbon.

  According to the present invention, it is possible to provide an electric storage device that has charging and discharging characteristics in which the voltage hardly changes with time and can increase the amount of energy that can be stored.

Sectional drawing which shows the structure of the electrical storage device of this invention.

  An embodiment of the present invention will be described.

  In the present invention, the positive electrode has a positive electrode active material layer having activated carbon and a transition metal oxide and a positive electrode current collector, and the negative electrode has a negative electrode active material layer and a negative electrode current collector that can be reversibly doped with lithium ions. , An electricity storage device comprising a unit that is alternately laminated or wound with a positive electrode and a negative electrode through a separator, the foil having a positive electrode current collector and a negative electrode current collector, a foil having holes penetrating the front and back surfaces, or Using an etching foil, using a non-aqueous solution containing lithium ions as the electrolyte, and placing the lithium source facing the unit in parallel with the negative electrode, charging with little change in voltage over time, It has been found that the amount of energy that can be stored and has discharge characteristics can be increased.

  According to the present invention, a voltage (for example, 4.5 V) to be charged by the positive electrode obtained by mixing a transition metal oxide having an oxidation-reduction potential between a voltage for charging and discharging a power storage device and activated carbon, and the aforementioned oxidation. In the region between the reduction potentials (for example, about −1.5 to +1.5 V as the standard electrode potential), the voltage changes almost linearly with time during charging and discharging. The same applies to the region between the voltage to be discharged (for example, 1.5 V) and the aforementioned oxidation-reduction potential. On the other hand, in the vicinity of the aforementioned oxidation-reduction potential region, the slope of the voltage with respect to time is gentle during charging and discharging.

  FIG. 1 is a cross-sectional view showing the structure of the electricity storage device of the present invention. As shown in FIG. 1, the positive electrode 9 includes a positive electrode active material layer 1 having activated carbon and a transition metal oxide on a positive electrode current collector 4, and the negative electrode 10 includes a lithium current collector 5 on a negative electrode current collector 5. The negative electrode active material layer 2 which has the active material which can be doped reversibly is provided. The separator 3 is disposed between the positive electrode 9 and the negative electrode 10.

  The positive electrode 9 and the negative electrode 10 are composed of units that are alternately stacked with separators 3 interposed therebetween, and are impregnated with an electrolytic solution 6 that is a non-aqueous solution containing lithium ions. A lithium metal 7 that is a lithium supply source is arranged on the outermost part of the unit so as to face the surface of the negative electrode active material layer 2, and is covered with an exterior material 8 to form an electricity storage device 11.

  The unit here is one in which the positive electrode and the negative electrode are alternately laminated via the separator so that the negative electrode is the outermost part. The negative electrode is a laminate of two or more, and the positive electrode is laminated of one or more. Say. Any number of units may be used according to the specified capacity. In order to increase the number of lithium supply sources, the number of units may be increased by decreasing the number of negative electrodes and positive electrodes in the unit.

  Further, when the unit is impregnated with an electrolytic solution that is a non-aqueous solution containing lithium ions, the negative electrode active material layer is doped with lithium ions from a lithium supply source. At this time, in the present invention, means for doping the negative electrode active material layer with lithium ions in advance is not particularly limited. For example, there are a method of electrochemically doping lithium ions into the negative electrode active material layer and a method of physically short-circuiting the negative electrode active material layer and lithium metal.

  As the lithium ion source, a material capable of supplying lithium ions, such as lithium metal or a lithium-aluminum alloy, can be used. The size of the width and length of the lithium supply source is preferably the same as that of the negative electrode active material layer or 1-2 mm smaller than that in order to dope lithium ions into the negative electrode active material layer. The thickness can be changed depending on the doping amount of lithium ions.

  As the material of the negative electrode current collector, various materials generally used for lithium ion secondary batteries and the like can be used. For the negative electrode current collector and the current collector for supplying lithium metal, stainless steel, copper, nickel Etc. can be used respectively. The current collector may be a rolled foil, an electrolytic foil, a penetrating foil having holes penetrating the front and back surfaces, or a net-like foil (hereinafter referred to as porous lath foil) such as expanded metal.

  The negative electrode active material that is the main component of the negative electrode active material layer is formed of a material that can be reversibly doped with lithium ions. For example, a graphite material used for a negative electrode of a lithium ion secondary battery, a carbon material such as a non-graphitizable carbon material and coke, a polyacene-based substance, and the like can be given. In view of reduction in resistance and cost, graphite material and non-graphitizable carbon material are more preferable.

  Aluminum, stainless steel, or the like can be used for the positive electrode current collector. In order to reduce the resistance and cost of the positive electrode active material layer, it is preferable to use an aluminum etching foil generally used for an aluminum electrolytic capacitor or an electric double layer capacitor. Since the aluminum etching foil increases the specific surface area by etching aluminum, the contact area with the positive electrode active material layer increases, the resistance decreases, and the output characteristics improve. Moreover, since it is a general-purpose product, low cost can be expected. Any etching process can be used for the aluminum etching foil. Various rolled foils, electrolytic foils, and porous lath foils used for lithium ion secondary batteries can also be used.

  One of the positive electrode active materials which are the main components of the positive electrode active material layer is formed from activated carbon which is a material capable of reversibly supporting anions or cations. For example, carbon materials such as polarizable phenol resin activated carbon, coconut shell activated carbon, petroleum coke activated carbon, and polyacene can be used.

  Another positive electrode active material that is a main component of the positive electrode active material layer is formed of a transition metal oxide that can be doped and dedoped with lithium ions. For example, a positive electrode material made of a group consisting of manganese, iron, cobalt, nickel, vanadium, molybdenum, titanium, zirconium, and copper, or a combination thereof can be used.

  The mixing mass ratio of the activated carbon and the transition metal oxide is preferably 15% or more and 75% or less as the mass ratio of the transition metal oxide. If it is less than 15%, there is no effect of charging and discharging at a constant current with a characteristic that the voltage changes almost linearly with time. If it is more than 75%, charging and discharging at a large current are not observed. The capacity of will decrease. That is, the output density is reduced.

  If necessary, a conductive additive and a binder are added to the positive electrode active material layer and the negative electrode active material layer. Examples of the conductive assistant include graphite, carbon black, ketjen black, vapor-grown carbon, and carbon nanotube, and carbon black and graphite are particularly preferable. As the binder, for example, a rubber-based binder such as styrene-butadiene rubber (SBR), a fluorine-containing resin such as polytetrafluoroethylene or polyvinylidene fluoride, or a thermoplastic resin such as polypropylene or polyethylene can be used.

  As the electrolytic solution, a non-aqueous solution containing lithium ions is used. Solvents of the electrolytic solution composed of a non-aqueous solution containing lithium ions are, for example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, Examples include methylene chloride and sulfolane. Furthermore, a mixed solvent obtained by mixing two or more of these solvents can also be used. Among these, it is preferable in view of characteristics to have at least either propylene carbonate or ethylene carbonate.

The electrolyte to be dissolved in the solvent, as long as it generates lithium upon ionization, for _{example, LiI, LiClO 4, LiAsF 6} , LiBF 4, LiPF 6 , and the like. These solutes are preferably 0.5 mol / L or more, and particularly preferably 0.5 mol / L or more and 2.0 mol / L or less in the solvent.

  Examples of the present invention are described in detail below.

  Hereinafter, Examples 1 to 7 and Comparative Example 1 will be described. In Examples, the mixing mass ratio of activated carbon and manganese dioxide was changed to arbitrary amounts, and in Comparative Example 1, only activated carbon was used as the positive electrode active material.

Example 1
10 parts by mass of a phenol-based activated carbon powder having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 90 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ were mixed, did.

  92 parts by mass of a positive electrode active material mixed with activated carbon and manganese dioxide and 8 parts by mass of graphite as a conductive agent are mixed with 3 parts by mass of styrene butadiene rubber as a binder, 3 parts by mass of carboxymethyl cellulose, and 200 masses of water as a solvent. And kneaded to obtain a slurry. Next, a porous lath aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, and the slurry was uniformly applied to both sides thereof, then dried and rolled and pressed, and the positive electrode active layer having a polarizable electrode layer thickness of 30 μm on both sides was obtained. A material layer was formed to obtain a positive electrode. The thickness of this positive electrode was 80 μm. In addition, a part of the end face of the positive electrode is formed with an electrode plate so that the current collector can be taken out in the form of a tab, and a positive electrode active material layer is not formed on both surfaces of the current collector. Was exposed.

  The powder obtained by mixing 88 parts by mass of the non-graphitizable material powder as the negative electrode active material and 6 parts by mass of acetylene black as the conductive agent, 5 parts by mass of styrene butadiene rubber as the binder, 4 parts by mass of carboxymethyl cellulose, and 200 parts by mass of water as the solvent. And kneaded to obtain a slurry. Next, a porous lath copper foil having a thickness of 10 μm is used as a negative electrode current collector, and the slurry is uniformly applied to both sides thereof, then dried and rolled and pressed, and the negative electrode active material having a polarizable electrode layer thickness of 20 μm on both sides. A layer was formed to obtain a negative electrode. The thickness of this negative electrode was 50 μm. In addition, a part of the end face of the negative electrode is formed with an electrode plate so that the current collector can be taken out in the form of a tab, and a negative electrode active material layer is not formed on both sides of the current collector of that part, and the copper foil Was exposed.

  As a separator, a thin plate of a natural cellulose material having a thickness of 30 μm was used. The size and shape of the separator was configured to be slightly larger than the shape excluding the electrode plate portion of the negative electrode.

  There were 4 positive electrodes, 5 negative electrodes, and 10 separators per unit. The dimensions excluding the exposed portion of the foil were 39 mm × 29 mm for the positive electrode and 40 mm × 30 mm for the negative electrode, and the dimensions of the separator were 41 mm × 31 mm. These three sheets were sequentially laminated in the order of separator, negative electrode, separator, positive electrode, and separator. A separator was always placed at the top and bottom of the unit.

  The manufactured unit was vacuum-treated at 130 ° C. for 6 hours using a vacuum dryer, and then the terminals were welded to the exposed portions of the positive and negative foils, placed in a container formed of an aluminum laminate film, and the outermost sides of the unit. In addition, lithium metal was disposed to face the negative electrode active material layer.

A non-aqueous electrolyte solution in which 1 mol / L LiPF ₆ was dissolved was injected into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a ratio of 1: 1, and sealed to produce a lithium ion capacitor.

  The manufactured lithium ion capacitor was subjected to constant voltage discharge so that 450 mAh / g of lithium ions was doped from the lithium metal into the negative electrode active material layer.

  The battery was charged at 3.8 V at a constant current and a constant voltage for 3 hours, and discharged at 4 mA (1 C) until the cell voltage reached 2.2 V. Next, charging was performed at 3.8 V at a constant current and constant voltage for 3 hours, and discharging was performed at 80 mA until the cell voltage reached 2.2 V, and the respective discharge capacities were calculated.

  When discharging at 4 mA, the change in voltage with time was recorded every second, and the ratio of the discharge capacity from 2.6 V to 2.4 V was determined for each discharge capacity.

(Example 2)
20 parts by mass of a powder of phenol-based activated carbon having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 80 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ are mixed with the positive electrode active material. did. Thereafter, a sample was prepared and measured in the same procedure as in Example 1.

(Example 3)
25 parts by mass of a powder of phenol-based activated carbon having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 75 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ were mixed in advance. Substance. Thereafter, a sample was prepared and measured in the same procedure as in Example 1.

Example 4
50 parts by mass of a phenol-based activated carbon powder having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 50 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ were mixed in advance. Substance. Thereafter, a sample was prepared and measured in the same procedure as in Example 1.

(Example 5)
75 parts by mass of a phenol-based activated carbon powder having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 25 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ were mixed in advance. Substance. Thereafter, a sample was prepared and measured in the same procedure as in Example 1.

(Example 6)
85 parts by mass of a phenol-based activated carbon powder having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 15 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ were mixed in advance. Substance. Thereafter, a sample was prepared and measured in the same procedure as in Example 1.

(Example 7)
90 parts by mass of a phenol-based activated carbon powder having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ and 10 parts by mass of manganese dioxide having a specific surface area of 150 m ² / g and a density of 5 g / cm ³ were mixed in advance. Substance. Thereafter, a sample was prepared and measured in the same procedure as in Example 1.

  Although Examples 1-7 use manganese dioxide, the same effect is seen even if other transition metal oxides such as iron, cobalt, nickel, vanadium, molybdenum, titanium, zirconium and copper are used.

(Comparative Example 1)
Comparative Example 1 was obtained by using only a powder of phenol-based activated carbon having a specific surface area of 1500 m ² / g and a density of 2 g / cm ³ as a positive electrode active material. Thereafter, a sample was prepared and measured in the same procedure as in Example 1. The discharge capacity at this time is 4 mA.

  Examples 1 to 7 and Comparative Example 1 are combined to show the mass ratio of activated carbon-manganese dioxide. The discharge capacity of 4 mA of Comparative Example 1 is set to 100%, and the discharge capacities of 4 mA and 80 mA are shown. Table 1 shows the ratio of the discharge capacity from 2.6 V to 2.4 V, assuming that the discharge capacity at 4 mA is 100%. This value shows the average value of the five lithium ion capacitors produced.

  Increasing the proportion of manganese dioxide simply increases the discharge capacity during 4 mA discharge. Furthermore, the discharge capacity increases from 2.6 V to 2.4 V when the discharge capacity at the time of discharge is 100% at 4 mA of the respective examples and comparative examples. These increases are due to the inherent capacity of the material and the redox potential. As a result, when the amount of manganese dioxide is increased, the amount of energy that can be stored is increased, and the portion where the voltage hardly changes with respect to time also increases.

  However, when the discharge capacity of 4 mA in Comparative Example 1 is set to 100% and discharge is performed at a current of 80 mA, the discharge capacity does not increase unlike the case of 4 mA discharge. Charging and discharging reactions of activated carbon are adsorption and desorption of ions, while manganese dioxide reactions are lithium ion doving and dedoping. It is known that adsorption / desorption of ions is faster than doving and dedoping.

  From Table 1, it can be seen that the discharge capacity of 80 mA in Examples 3 to 7 is equivalent to the discharge capacity of 4 mA in Comparative Example 1, and the capacity is equivalent to that in Comparative Example 1 even when a large current is passed. When the amount of manganese dioxide in Examples 1 and 2 (80 to 90%) is reached, the discharge capacity of 80 mA is reduced, so that it is not suitable for applications using a large current.

  According to the present invention, the active material of the positive electrode active material layer is combined with activated carbon and a transition metal oxide, so that it has a charge / discharge characteristic in which the voltage hardly changes with time, and even when a large current is passed. It has been confirmed that it is possible to provide an electricity storage device that can increase the amount of energy that can be stored without any decrease.

  The embodiments of the present invention have been described above using the embodiments. However, the present invention is not limited to these embodiments, and the present invention is not limited to the scope of the present invention. Included in the invention. That is, various changes and modifications that can be naturally made by those skilled in the art are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 2 Negative electrode active material layer 3 Separator 4 Positive electrode collector 5 Negative electrode collector 6 Electrolytic solution 7 Lithium metal 8 Exterior material 9 Positive electrode 10 Negative electrode 11 Power storage device

Claims (3)

  A non-aqueous electrolyte containing lithium ions, a positive electrode in which a positive electrode active material layer having activated carbon and a transition metal oxide is formed on a positive electrode current collector, and lithium ion reversibly doped on the negative electrode current collector A negative electrode on which a possible negative electrode active material layer is formed, wherein the positive electrode and the negative electrode are alternately stacked or wound through a separator, and a lithium supply source is arranged to face the negative electrode Power storage device.   The electricity storage device according to claim 1, wherein the transition metal oxide is made of manganese oxide.   The power storage device according to claim 1, wherein a mixing ratio of the activated carbon and the transition metal oxide in the positive electrode active material layer is 15% or more and 75% or less in terms of a mass ratio of the transition metal oxide.

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