JP2006286919A - Lithium ion capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion capacitor which has high energy density, power density, a large capacity, and offers high safety. <P>SOLUTION: The lithium ion capacitor has a lithium salt nonproton organic solvent solution which serves as a positive electrode, a negative electrode, and an electrolyte, a positive electrode active material which can carry lithium ions and/or anions reversibly, and a negative active material which can carry lithium ions reversibly. The positive electrode registers a potential of 2.0 V or lower after short-circuiting the positive electrode and negative electrode. The capacitor also includes a positive electrode current collector and a negative electrode current collector, each collector having holes penetrating its front/back surfaces; and a cell structure which is formed by winding the positive/negative electrodes via a separator, or laminating them alternately into three layers. A lithium ion supply source which is arranged to be counter to the wound or laminated positive/negative electrodes, is brought into electrochemical contact with the positive electrode and/or the negative electrode which causes the positive electrode and/or the negative electrode to carry lithium ions in advance. A counter area between the lithium ion supply source and the negative electrode is 75 to 100% of the area of the negative electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-capacity lithium ion capacitor with high energy density and high output density.

In recent years, a battery using a carbon material such as graphite for the negative electrode and a lithium-containing metal oxide such as LiCoO _{2 for} the positive electrode has been proposed. This battery is a so-called rocking chair type battery in which lithium is supplied from the lithium-containing metal oxide of the positive electrode to the negative electrode by charging after the battery is assembled, and further, the negative electrode lithium is returned to the positive electrode in the discharge. This is called a lithium ion secondary battery, and is distinguished from a lithium battery using lithium metal. This battery is characterized by high voltage, high capacity, and high safety.

  In addition, while environmental problems are being highlighted, development of a clean energy storage system using solar power generation or wind power generation, and a power source for an electric vehicle or a hybrid electric vehicle that replaces a gasoline vehicle has been actively conducted. Furthermore, recently, in-vehicle devices and equipment such as power windows and IT-related equipment have become more sophisticated and functional, and new power sources are being demanded in terms of energy density and output density.

  In recent years, a power storage device called a hybrid capacitor, which combines the power storage principles of a lithium ion secondary battery and an electric double layer capacitor, has been attracting attention as a power storage device for such applications that require high energy density and high output characteristics. . As one of them, a lithium ion can be occluded and desorbed by a chemical method or an electrochemical method in advance and occluded and supported (hereinafter sometimes referred to as doping) to lower the negative electrode potential. An organic electrolyte capacitor using a carbon material that can significantly increase the energy density as a negative electrode has been proposed (see, for example, Patent Document 1).

  Although this type of organic electrolyte capacitor is expected to have high performance, there are problems in that it takes a very long time when lithium ions are doped in advance on the negative electrode and that lithium ions are uniformly supported on the entire negative electrode. In particular, it has been difficult to put into practical use in a large-sized high-capacity cell such as a cylindrical device in which electrodes are wound or a square battery in which a plurality of electrodes are stacked.

  As a method for solving such a problem, the positive electrode current collector and the negative electrode current collector each have holes penetrating the front and back surfaces, and the negative electrode active material can reversibly carry lithium ions, and faces the negative electrode or the positive electrode. There has been proposed an organic electrolyte battery in which lithium ions are supported on a negative electrode by electrochemical contact with lithium metal disposed in a row (see, for example, Patent Document 2).

  In the organic electrolyte battery, since a hole penetrating the front and back surfaces is provided in the electrode current collector, lithium ions can move between the front and back surfaces of the electrode current collector without being blocked by the electrode current collector. Also in the power storage device having the configuration, lithium ions can be electrochemically supported not only on the negative electrode arranged in the vicinity of the lithium metal but also on the negative electrode arranged away from the lithium metal through the through hole.

JP-A-8-107048 (page 2, column 2, lines 38 to 47) International Publication No. WO98 / 033227 (page 11, line 4 to page 12, line 27)

  As described above, a negative electrode in which lithium ions are occluded in advance in a carbon material or the like that can occlude and desorb lithium ions, that is, before charging, has a lower potential than activated carbon used for an electric double layer capacitor. The withstand voltage of the cell combined with the positive electrode activated carbon is improved, and the capacity of the negative electrode is much larger than that of the activated carbon. Therefore, the organic electrolyte capacitor (lithium ion capacitor) provided with the negative electrode has a high energy density.

  In the lithium ion capacitor, the cell is configured as an electrode laminate in which a positive electrode and a negative electrode are alternately laminated via a separator, and the negative electrode is a lithium disposed outside the electrode laminate and facing the positive electrode and / or the negative electrode. Lithium ions are sequentially doped from the metal through the through holes of the electrode current collector. In this case, it is preferable that all of the lithium metal previously set according to the amount of lithium ions doped in the negative electrode is uniformly doped as lithium ions in the negative electrode.

  However, if the area of the lithium metal disposed in the cell is larger than the area of the opposing negative electrode, the lithium metal may remain in the cell without being doped into the negative electrode. Since the amount of lithium metal is set in advance according to the amount of doping in advance in the negative electrode, if lithium metal remains in the cell in this way, the lithium ion cannot be doped into the negative electrode or the remaining lithium Safety such as the possibility that the metal reacts with the electrolyte in the cell and the characteristics deteriorate, causing a short circuit, or the lithium metal generates heat or ignites when the outer case is damaged Cause problems such as loss of performance.

  On the other hand, if the area of the lithium metal is excessively smaller than the area of the opposing negative electrode, a predetermined amount of lithium metal is not doped in the entire negative electrode, which may result in failure to obtain the initial performance and characteristics, and in some cases the lithium metal There was a problem that metal remained or the capacity of the cell was reduced. In addition, when the area of the lithium metal is the same as the area of the opposing negative electrode, it is difficult to completely match both in the cell assembly, resulting in a decrease in assembly workability. In some cases, the lithium metal protrudes from the cell and remains in the cell.

  The present invention solves such a problem, and a lithium ion capacitor in which a predetermined amount of lithium ions can be preliminarily doped into the negative electrode and / or the positive electrode without leaving any lithium metal in the cell, and the assembly workability of the cell is excellent. The purpose is to provide.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research on a method capable of doping a predetermined amount of lithium ions into the negative electrode and / or the positive electrode without leaving the lithium metal in the cell. By making it a little smaller, it was found that lithium metal can be doped without leaving it in the cell, and how much the lithium metal can be reduced relative to the opposing negative electrode, a predetermined amount of lithium ions can be added to the negative electrode in the cell. The present inventors have completed the present invention by investigating whether doping can be performed without leaving a residue. That is, the present invention provides the following lithium ion capacitor.

(1) A positive electrode, a negative electrode, and an electrolyte solution of an aprotic organic solvent of lithium salt as an electrolyte, the positive electrode active material is a material capable of reversibly supporting lithium ions and / or anions, and the negative electrode active material is lithium ions A lithium ion capacitor in which the potential of the positive electrode becomes 2.0 V or less after the positive electrode and the negative electrode are short-circuited, and the positive electrode current collector and the negative electrode current collector are respectively Lithium provided with a hole penetrating the back surface and having a cell configuration in which a positive electrode and a negative electrode are wound with a separator interposed therebetween or alternately laminated in three or more layers, and are disposed facing the wound or laminated negative electrode and positive electrode The lithium ion is previously supported on the negative electrode and / or the positive electrode by electrochemical contact between the ion supply source and the negative electrode and / or the positive electrode. The opposing area of the negative electrode more than 75% of the negative electrode area, a lithium ion capacitor, which is a less than 100%.
(2) The lithium ion capacitor according to (1), wherein the lithium ion supply source is disposed so as not to protrude from the negative electrode facing the lithium ion supply source.
(3) The above-mentioned (1) or (2), wherein when the lithium ion supply source and the negative electrode are curved, the facing area between the lithium ion supply source and the negative electrode is a projected area of each facing portion. Lithium ion capacitor.
(4) The electrode stack in which the positive electrode and the negative electrode are alternately wound or stacked with a separator interposed therebetween is a separator, the inner side of the separator is a negative electrode, and the lithium ion supply source faces the negative electrode (1) The lithium ion capacitor of (2) or (3).
(5) The negative electrode is a polyacene organic semiconductor (PAS) which is a heat-treated product of an aromatic condensation polymer and has a polyacene skeleton structure in which the atomic ratio of hydrogen atom / carbon atom is 0.50 to 0.05. The lithium ion capacitor according to any one of (1) to (4) above.
(6) The negative electrode active material has a capacitance per unit weight that is at least three times that of the positive electrode active material, and the weight of the positive electrode active material is greater than the weight of the negative electrode active material ( The lithium ion capacitor according to any one of 1) to (5).

  According to the lithium ion capacitor of the present invention, as described above, the facing area between the lithium ion supply source and the negative electrode is 75% or more and less than 100% of the negative electrode area, so that the lithium ion supply source does not remain in the cell. Since the negative electrode can be doped with lithium ions, a highly safe and high quality lithium ion capacitor can be obtained.

  Further, since the area of the lithium ion supply source is smaller than the area of the negative electrode facing the lithium ion supply source, it becomes easy to arrange the lithium ion supply source in the cell so as not to protrude from the negative electrode, and the assembly workability of the cell is improved. Productivity can be improved.

  The lithium ion capacitor of the present invention (hereinafter sometimes referred to as LIC) includes a positive electrode, a negative electrode, and an aprotic organic electrolyte of a lithium salt as an electrolyte, and the positive electrode active material reversibly converts lithium ions and / or anions. The negative electrode active material is a material capable of reversibly supporting lithium ions, and the positive electrode and negative electrode potentials after the positive electrode and the negative electrode are short-circuited have 2.0 V or less.

  In conventional electric double layer capacitors, the same active material (mainly activated carbon) is usually used in substantially the same amount for the positive electrode and the negative electrode. This active material has a potential of about 3 V when the cell is assembled. When the capacitor is charged, an anion forms an electric double layer on the positive electrode surface, and the positive electrode potential rises. Forms an electric double layer and the potential drops. Conversely, during discharge, anions are released from the positive electrode and cations from the negative electrode into the electrolyte, respectively, and the potential decreases and rises to return to around 3V. As described above, since the normal carbon material has a potential of about 3 V, the organic electrolyte capacitor using the carbon material for both the positive electrode and the negative electrode has the positive electrode and the negative electrode both short-circuited after being short-circuited. It becomes about 3V.

On the other hand, in the LIC of the present invention, as described above, the potential of the positive electrode after short-circuiting the positive electrode and the negative electrode is 2.0 V (Li / Li ⁺ , the same shall apply hereinafter) or less. That is, in the present invention, an active material capable of reversibly supporting lithium ions and / or anions is used for the positive electrode, and an active material capable of reversibly supporting lithium ions is used for the negative electrode. Lithium ions are previously supported on the negative electrode and / or the positive electrode so that the potential between the positive electrode and the negative electrode is 2.0 V or less.

  In the present invention, the potential of the positive electrode after the positive electrode and the negative electrode are short-circuited is 2 V or less. The potential of the positive electrode determined by one of the following two methods (A) or (B) is 2 V or less. Refers to cases. That is, (A) After doping with lithium ions, the positive electrode terminal and the negative electrode terminal of the capacitor cell are directly coupled with a conductive wire and left for 12 hours or more, then the short circuit is released, and within 0.5 to 1.5 hours Measured positive electrode potential, (B) Charge-discharge tester discharges constant current to 0V over 12 hours and then leaves positive electrode terminal and negative electrode terminal connected with lead wire for 12 hours or more, then releases short circuit Positive electrode potential measured within 0.5 to 1.5 hours.

  In the present invention, the positive electrode potential after the positive electrode and the negative electrode are short-circuited is 2.0 V or less, not only immediately after the lithium ions are doped, but in the charged state, discharged state or charged state. The positive electrode potential after short-circuiting is 2.0 V or less in any state, such as when short-circuiting after repeating discharge.

In the present invention, the fact that the positive electrode potential after the positive electrode and the negative electrode are short-circuited is 2.0 V or less will be described in detail below. As described above, activated carbon and carbon materials usually have a potential of about 3 V (Li / Li ⁺ ), and when the cell is assembled using activated carbon for both the positive electrode and the negative electrode, both potentials are about 3 V. Even if it is short-circuited, the positive electrode potential is about 3 V regardless. The same applies to a so-called hybrid capacitor using activated carbon as the positive electrode and carbon material such as graphite or non-graphitizable carbon used in the lithium ion secondary battery as the negative electrode. Therefore, even if a short circuit occurs, the positive electrode potential is about 3 V regardless. Although depending on the weight balance between the positive electrode and the negative electrode, when charged, the potential of the negative electrode transitions to around 0 V, so that the charging voltage can be increased, so that the capacitor has a high voltage and a high energy density. Generally, the upper limit of the charging voltage is determined to be a voltage at which the electrolyte solution does not decompose due to the increase in the positive electrode potential. Therefore, when the positive electrode potential is set as the upper limit, the charging voltage can be increased by the amount of decrease in the negative electrode potential. It is. However, in the above-described hybrid capacitor in which the positive electrode potential is about 3 V at the time of short circuit, when the upper limit potential of the positive electrode is 4.0 V, for example, the positive electrode potential at the time of discharge is up to 3.0 V, and the potential change of the positive electrode is 1. The capacity of the positive electrode of about 0 V is not fully utilized. Furthermore, when lithium ions are inserted (charged) and desorbed (discharged) into the negative electrode, the initial charge / discharge efficiency is often low, and it is known that there are lithium ions that cannot be desorbed during discharge. This is explained when it is consumed in the decomposition of the electrolyte solution on the negative electrode surface or trapped in the structural defect part of the carbon material. In this case, the charge / discharge of the negative electrode is compared with the charge / discharge efficiency of the positive electrode. When the efficiency is lowered and the cell is short-circuited after repeated charging and discharging, the positive electrode potential becomes higher than 3 V, and the utilization capacity further decreases. That is, the positive electrode can be discharged from 4.0 V to 2.0 V. However, when only 4.0 V to 3.0 V can be used, only half of the usage capacity is used. It will not be.

  In order to increase not only high voltage and high energy density but also high capacity and energy density of the hybrid capacitor, it is necessary to improve the capacity of the positive electrode.

  If the positive electrode potential after the short circuit falls below 3.0V, the utilization capacity increases and the capacity increases. In order to be 2.0 V or less, it is preferable to charge not only the amount charged by charging / discharging the cell but also separately charging lithium ions from a lithium ion supply source such as lithium metal to the negative electrode. Since lithium ions are supplied from other than the positive electrode and the negative electrode, when they are short-circuited, the equilibrium potentials of the positive electrode, the negative electrode, and the lithium metal are reached, so that both the positive electrode potential and the negative electrode potential are 3.0 V or less. As the amount of lithium metal increases, the equilibrium potential decreases. If the negative electrode material and the positive electrode material change, the equilibrium potential also changes. Therefore, it is necessary to adjust the amount of lithium ions supported on the negative electrode in view of the characteristics of the negative electrode material and the positive electrode material so that the positive electrode potential after the short circuit becomes 2.0 V or less. It is.

  In the LIC of the present invention, the positive electrode potential after the positive electrode and the negative electrode are short-circuited is 2.0 V or less, as described above, lithium ions are supplied to the positive electrode and / or the negative electrode from other than the positive electrode and the negative electrode of the LIC. It is that it has been. The supply of lithium ions may be either one or both of the negative electrode and the positive electrode. For example, when activated carbon is used for the positive electrode, if the amount of lithium ion supported increases and the positive electrode potential decreases, the lithium ion is irreversibly consumed. Since problems such as a decrease in cell capacity may occur, the amount of lithium ions supplied to the negative electrode and the positive electrode needs to be appropriately controlled so as not to cause problems. In any case, since the lithium ions previously supplied to the positive electrode and / or the negative electrode are supplied to the negative electrode by charging the cell, the negative electrode potential decreases.

When the positive electrode potential after the positive electrode and the negative electrode are short-circuited is higher than 2.0 V, the energy density of the cell is small because the amount of lithium ions supplied to the positive electrode and / or the negative electrode is small. As the supply amount of lithium ions increases, the potential of the positive electrode after the positive electrode and the negative electrode are short-circuited becomes lower and the energy density is improved. In order to obtain a high energy density, 2.0 V or less is preferable, and in order to obtain a higher energy density, 1.0 V (Li / Li ⁺ ) or less is preferable. In other words, the positive electrode potential after the positive electrode and the negative electrode are short-circuited is reduced, which means that the amount of lithium ions supplied to the negative electrode by charging the cell increases, and the capacitance of the negative electrode increases. At the same time, the potential change amount of the negative electrode is reduced. As a result, the potential change amount of the positive electrode is increased, the capacitance and capacity of the cell are increased, and a high energy density is obtained. Further, when the positive electrode potential is less than 1.0 V, although depending on the positive electrode active material, problems such as gas generation and irreversible consumption of lithium ions occur, so that it is difficult to measure the positive electrode potential. On the other hand, when the positive electrode potential becomes too low, the negative electrode weight is excessive, and conversely the energy density decreases. Generally, it is 0.1 V or more, preferably 0.3 V or more.

  In the present invention, the capacitance and capacitance are defined as follows. The capacitance of the cell indicates the slope of the discharge curve of the cell, the unit is F (farad), and the capacitance per unit weight of the cell is the positive electrode active material in which the capacitance of the cell is filled in the cell It is the value divided by the total weight of the weight and the weight of the negative electrode active material, the unit is F / g, the capacitance of the positive electrode is the slope of the discharge curve of the positive electrode, the unit is F, the electrostatic capacity per unit weight of the positive electrode The capacity is a value obtained by dividing the capacitance of the positive electrode by the weight of the positive electrode active material filled in the cell. The unit is F / g. The capacitance of the negative electrode is the capacitance of the negative electrode in the cell. The value is divided by the weight of the filled negative electrode active material, and the unit is F / g.

  Furthermore, the cell capacity or the difference between the discharge start voltage and the discharge end voltage of the cell, that is, the product of the voltage change amount and the capacitance of the cell, the unit is C (coulomb), and 1 C is a current of 1 A per second. Since this is the amount of charge when it flows, it is converted to mAh in this patent. The positive electrode capacity is the product of the difference between the positive electrode potential at the start of discharge and the positive electrode potential at the end of discharge (positive electrode potential change amount) and the positive electrode capacitance. The unit is C or mAh. The difference between the negative electrode potential and the negative electrode potential at the end of discharge (amount of change in negative electrode potential) and the capacitance of the negative electrode, and the unit is C or mAh. These cell capacity, positive electrode capacity, and negative electrode capacity coincide with each other.

  Next, the structure of the lithium ion capacitor of this invention is demonstrated according to drawing. The drawings shown below illustrate preferred embodiments of the present invention, and the present invention is not limited thereto. FIG. 1 is a cross-sectional view of a film-type cell that is a typical lithium ion capacitor (hereinafter also referred to as a cell) according to the present invention. FIG. 2 is a plan view of FIG. Shows a cross section taken along the line AA 'in FIG.

  In the present invention, as shown in FIG. 1, the cell is formed by alternately laminating positive electrodes 1 and negative electrodes 2 via separators 3 to form an electrode laminate 11 and placing it in an outer container 5. A lithium metal (lithium electrode) 4 is arranged as a lithium ion supply source so as to face the positive electrode 1 and the negative electrode 2 stacked on the upper part. Each of the stacked positive electrodes 1 is connected to the positive electrode connection terminal 9 by, for example, welding by the extraction portion 6, and each of the negative electrode 2 and the lithium metal 4 is connected to the negative electrode connection terminal 10 by the extraction portion 7 and the lithium electrode extraction portion 8, respectively. Has been. In this example, the positive electrode connection terminal 9 and the negative electrode connection terminal 10 are provided at the left end and the right end of the film type cell as shown in FIG. 2, respectively, but the positions of these connection terminals can be changed as appropriate.

  When an electrolyte (electrolyte) capable of transporting lithium ions is injected into the thus configured cell and sealed, and left in this state for a predetermined time (for example, 10 days), the lithium metal 4 and the anode 2 Are short-circuited, so that the negative electrode 2 can be preliminarily doped with lithium ions. In the present invention, the “positive electrode” means that a current flows out during discharging, the electrode into which current flows during charging, and the “negative electrode” refers to a current flowing during discharging, and during charging. It means the pole where the current flows out.

  In this example, the cell is composed of two positive electrode layers and three negative electrode layers in total, depending on the number of active material layers. The number of positive electrode and negative electrode layers incorporated in the cell depends on the type of cell and the lithium disposed in the cell. Although it differs depending on the number of metal layers and the like, it is usually about 10 to 20 layers. Further, the electrode laminate 11 can be accommodated in the exterior container 5 in the vertical direction.

  In the electrode laminate 11 constituting the cell, the outermost part (upper part in FIG. 1) on the side where the lithium metal 4 is arranged is the separator 3, and the negative electrode 2 is preferably installed inside thereof. By using the separator 3 as the outermost part of the electrode laminate 11, it is possible to prevent the lithium metal 4 from coming into direct contact with the electrode and prevent damage to the electrode surface due to abrupt doping after injection of the electrolyte. Further, when the electrode laminate 11 is made in advance and then installed in the outer container 5, the electrodes can be covered with the separator 3 for protection. Further, by making the inner side of the separator 3 a negative electrode, there is an advantage that there is no problem even if the negative electrode 2 and the lithium metal 4 are short-circuited.

  FIG. 3 shows the negative electrode 2 laminated inside the electrode laminate 11 with a part cut away. The negative electrode 2 is formed as a negative electrode active material layer (this negative electrode active material layer is shown as the negative electrode 2 in the figure) on the negative electrode current collector 2 a, and the negative electrode 2 is laminated inside the electrode laminate 11. The negative electrode current collector 2a is preferably formed on both sides. However, in the negative electrode laminated on the outermost part of the electrode laminate 11, the negative electrode active material layer can usually be formed only on one surface (inner surface) of the negative electrode current collector 2a.

  As shown in FIG. 3, the negative electrode current collector 2a is a porous material provided with holes 12 penetrating the front and back surfaces, and includes a takeout portion 7 at a part of the side end portion thereof. Although not shown, the positive electrode 1 can be manufactured in the same manner as the negative electrode 2 except that the positive electrode 1 is formed of a positive electrode active material layer. Thus, by making the negative electrode current collector 2a and the positive electrode current collector 1a into a porous material, lithium ions freely move between the electrodes from the end of the electrode laminate 11 through the through holes of both current collectors. In addition, all the negative electrodes of the electrode stack 11 can be doped with lithium ions.

  On the other hand, the lithium metal 4 disposed so as to face the positive electrode 1 and the negative electrode 2 of the cell is formed by pressing and bonding a lithium metal on both sides of the lithium electrode current collector 4a, preferably on the both sides. The lithium electrode current collector 4a preferably has a porous structure like the negative electrode current collector 2a so that the lithium metal can be easily crimped and lithium ions can pass through if necessary.

  In the lithium ion capacitor having the above-described configuration, the present invention provides a negative electrode disposed in the cell, and a facing area of the lithium metal disposed facing the positive electrode is 75% or more of a facing area of the negative electrode facing the lithium metal. , Less than 100%, preferably 85% or more and 98% or less, more preferably 90% or more and 95% or less.

  Here, the facing area of the lithium metal is the area of the region where the lithium metal and the negative electrode overlap. When the negative electrode is larger and the lithium metal completely fits in the negative electrode area, it is the area of the lithium metal itself. Specifically, it is the area of the portion where the lithium metal is crimped or adhered to the lithium electrode current collector. Conversely, when the lithium metal is larger and the negative electrode completely fits in the lithium metal area, the area of the negative electrode becomes the opposite area of the lithium metal. In general, in a stacked type cell such as a square type or a film type, a negative electrode and a positive electrode having substantially the same size are stacked to form an electrode stack, and the electrode stack is opposed to lithium metal. The smaller the area of the negative electrode or the area of the lithium metal is the opposing area.

  On the other hand, in a wound type cell in which an electrode laminate is wound, a strip-shaped negative electrode is wound to form an electrode laminate. In such a case, since the negative electrode and the lithium metal are curved, the areas of the negative electrode and the lithium metal are projected areas, and the overlapping region is the opposing area.

  Next, the film type lithium ion capacitor of FIG. 1 will be described in detail as an example. FIG. 4 schematically shows the electrode laminate 11 and the lithium metal 4 of FIG. As shown in the figure, the electrode laminate 11 is configured by alternately laminating positive electrodes 1 and negative electrodes 2 with separators 3 interposed between them, and a separator 3 is installed at the outermost part, and the negative electrode 2 is placed inside the separator 3. is set up. The lithium metal 4 is disposed to face the negative electrode 2 of the electrode laminate 11.

  In the present invention, the facing area S of the lithium metal 4 is 75% or more and less than 100% of the facing area T of the negative electrode 2 in the above. In this example, for easy understanding, the lateral dimension of the lithium metal 4 is conveniently shortened from the lateral dimension of the negative electrode 2 so that the opposing area S of the lithium metal 4 is smaller than the opposing area T of the negative electrode 2. The vertical dimension or both vertical and horizontal dimensions may be reduced with respect to the dimension of the negative electrode 2. When the facing area S of the lithium metal 4 is less than 75% of the facing area T of the negative electrode 2, the facing surface of the lithium metal 4 is too small with respect to the negative electrode 2, so that the entire negative electrode is sufficiently doped with lithium ions without unevenness. Since the doping of lithium ions is concentrated locally, the doping of some of the negative electrode may be applied and deteriorated, or lithium metal may remain, etc. Further, if it is 100% or more, it protrudes from the negative electrode 2 when the lithium metal 4 is installed (even if it is 100%, it easily protrudes due to misalignment), and a part of the lithium metal in this protruding portion is not doped into the negative electrode. Therefore, it is not preferable in terms of cell characteristics and safety.

  Further, even if it is less than 100%, if it is close to 100%, it is difficult to dispose the lithium metal 4 so as not to protrude from the negative electrode 2, so that the facing area S of the lithium metal 4 is opposite to that of the negative electrode 2. It is preferably 85% or more and 98% or less of the area T.

  Even if the facing area S of the lithium metal 4 is less than 100% of the facing area T of the negative electrode 2, if the lithium metal 4 is not accurately aligned with the negative electrode 2, a part of the lithium metal 4 is negative. It protrudes from 2 and causes lithium metal to remain in the cell. Therefore, when arranging the lithium metal 4, it is important not to protrude from the negative electrode 2.

  The reason why the facing area of the lithium metal 4 is thus determined in relation to the facing area of the outermost negative electrode 2 is that lithium ions are doped into the negative electrode 2 mainly in an actual cell, and in the cell assembly process. By arranging the lithium metal 4 in alignment with the negative electrode 2 located on the outermost side of the electrode laminate.

  FIGS. 5 and 6 are schematic cross-sectional views showing other embodiments of a rectangular laminated type lithium ion capacitor, respectively. FIG. 5 shows an example in which the lithium metal 4 is disposed on the upper and lower portions of the electrode stack 11 constituting the cell, and FIG. 6 shows that the cell is composed of two or more electrode stacks 11 between the electrode stacks 11. This is an example in which lithium metal 4 is disposed. In these examples, similarly, the same effect can be obtained by setting the facing area of the lithium metal 4 to 75% or more and less than 100% of the facing area of the negative electrode 2 facing the lithium metal 4.

  FIG. 7 is a sectional view of a wound type lithium ion capacitor according to another embodiment of the present invention. In this example, a belt-like positive electrode 1 and a negative electrode 2 are wound in a circle with a separator 3 interposed therebetween, and a cylindrical electrode stack 11 is formed with the separator 3 as the outermost part and the negative electrode 2 inside thereof. For example, a lithium metal 4 is disposed on the opposite side of the laminate so as to face the negative electrode 2 to constitute a cell. In FIG. 7, the heights of the positive electrode 1, the negative electrode 2, and the lithium metal 4 are substantially the same, and the facing portion of the lithium metal 4 and the negative electrode 2 is a substantially cylindrical curved surface. Further, all electrode current collectors are not shown.

  In such a wound type lithium ion capacitor, the facing area of the lithium metal 4 is the projected area S of the substantially cylindrical lithium metal, and the facing area of the negative electrode 2 facing the lithium metal is facing the lithium metal 4. This is the projected area T of the semi-cylindrical surface of the substantially cylindrical negative electrode where the area of the outermost part of the electrode laminate 11 facing the lithium metal 4 is maximized. Therefore, in this example, the projected area S of the lithium metal 4 is set to 75% or more and less than 100% of the projected area T of the negative electrode 2 facing the lithium metal.

  FIG. 8 is a cross-sectional view of another lithium ion capacitor using the wound electrode laminate. This example is a flat wound type lithium ion capacitor, and the lithium metal 4 is installed at the center of the flat electrode laminate 11. The facing area S of the lithium metal 4 and the facing area T of the negative electrode 2 facing the lithium metal in this example are as shown. By making the facing area S of the lithium metal 4 75% or more and less than 100% of the facing area T of the negative electrode 2 facing the lithium metal 4, lithium ions are left in the negative electrode and / or positive electrode without leaving any lithium metal in the cell. Can be doped. The lithium metal 4 may be installed outside the flat electrode laminate 11, and in this case as well, the facing area S of the lithium metal 4 is 75% or more of the facing area T of the negative electrode 2 facing the lithium metal 4. , Less than 100%.

Below, the main elements which comprise the lithium ion capacitor of this invention are demonstrated one by one.
As the positive electrode current collector and the negative electrode current collector of the present invention, various materials generally proposed for applications such as organic electrolyte batteries can be used. The positive electrode current collector is made of aluminum, stainless steel, or the like. Stainless steel, copper, nickel and the like can be suitably used for the body, and various shapes such as foil and net can be used. In particular, in order to support lithium ions in advance on the negative electrode and / or the positive electrode, those having holes penetrating the front and back surfaces are preferable. For example, expanded metal, punching metal, metal net, foam, or through holes are provided by etching. A porous foil etc. can be mentioned. The through-hole of the electrode current collector can be appropriately set to be round, square, or the like.
More preferably, before forming the electrode, at least a part of the through-hole of the electrode current collector is blocked with a conductive material that does not easily fall off, and a positive electrode and a negative electrode are formed thereon using an active substance. As a result, the productivity of the electrode is improved, the problem of a decrease in the reliability of the capacitor due to the dropping of the electrode is solved, and furthermore, the thickness of the electrode including the current collector is reduced, so that the high energy density and the high Power density can be realized.
The shape and number of through-holes in the electrode current collector are blocked by a conductive material so that lithium ions in the electrolyte described later can move between the front and back of the electrode without being blocked by the electrode current collector. It can be set as appropriate so that it is easy to do.

  The porosity of this electrode current collector is defined as that obtained by converting the ratio of {1- (current collector weight / current collector true specific gravity) / (current collector apparent volume)} into a percentage. The porosity of the electrode current collector used in the present invention is usually 10 to 79%, preferably 20 to 60%. It is desirable that the porosity and the pore diameter of the electrode current collector are appropriately selected within the above-mentioned range in consideration of the cell structure and productivity.

  The negative electrode active material is not particularly limited as long as it can reversibly carry lithium ions. For example, it is a heat-treated product of graphite, non-graphitizable carbon, and aromatic condensation polymer, and includes hydrogen atoms / carbon atoms. Examples thereof include a polyacene organic semiconductor (PAS) having a polyacene skeleton structure with a ratio of 0.50 to 0.05. Among these, PAS is more preferable in that a high capacity can be obtained. Capacitance of 650 F / g or more can be obtained by discharging after charging (charging) 400 mAh / g of lithium ions on PAS, and static electricity of 750 F / g or more can be obtained by charging lithium ions of 500 mAh / g or more. Capacitance can be obtained. From this, it can be seen that PAS has a very large capacitance.

  In a preferred embodiment of the present invention, when an active material having an amorphous structure such as PAS is used for the negative electrode, the potential decreases as the amount of lithium ions to be carried increases, so that the withstand voltage (charging voltage) of the obtained power storage device In addition, the rate of increase in voltage during discharge (the slope of the discharge curve) decreases, so that the amount of lithium ions is within the range of lithium ion storage capacity of the active material, depending on the required operating voltage of the power storage device. It is desirable to set appropriately.

  In addition, since PAS has an amorphous structure, there is no structural change such as swelling / shrinkage with respect to insertion / extraction of lithium ions, so that cycle characteristics are excellent, and isotropic to insertion / extraction of lithium ions. Since it has a molecular structure (higher order structure), it is suitable as a negative electrode material because it has excellent characteristics in rapid charge and rapid discharge.

  The aromatic condensation polymer that is a precursor of PAS is a condensate of an aromatic hydrocarbon compound and an aldehyde. As the aromatic hydrocarbon compound, so-called phenols such as phenol, cresol, xylenol and the like can be suitably used. For example, the following formula

（ここで、ｘ及びｙはそれぞれ独立に、０、１または２である）
で表されるメチレン・ビスフェノール類であることができ、あるいはヒドロキシ・ビフェニル類、ヒドロキシナフタレン類であることもできる。これらの中でも、実用的にはフェノール類、特にフェノールが好適である。

(Where x and y are each independently 0, 1 or 2)
Or a biphenyl or a hydroxynaphthalene. Among these, phenols, particularly phenol, are preferable for practical use.

  As the aromatic condensed polymer, a part of the aromatic hydrocarbon compound having a phenolic hydroxyl group is substituted with an aromatic hydrocarbon compound having no phenolic hydroxyl group, such as xylene, toluene, aniline, etc. It is also possible to use a modified aromatic condensation polymer such as a condensate of phenol, xylene and formaldehyde. Furthermore, a modified aromatic polymer substituted with melamine or urea can be used, and a furan resin is also suitable.

In the present invention, PAS is used as an insoluble and infusible substrate, and the insoluble and infusible substrate can also be produced, for example, from the aromatic condensation polymer as follows. That is, the aromatic condensation polymer is gradually heated to a suitable temperature of 400 to 800 ° C. in a non-oxidizing atmosphere (including a vacuum), whereby a hydrogen atom / carbon atom ratio (hereinafter referred to as H). / C)) is 0.5 to 0.05, preferably 0.35 to 0.10.
However, the method for producing an insoluble and infusible substrate is not limited to this, and is, for example, a method described in Japanese Patent Publication No. 3-24024 and the like, and has the above H / C and 600 m ² / g. It is also possible to obtain an insoluble and infusible substrate having a specific surface area by the above BET method.

  According to X-ray diffraction (CuKα), the insoluble and infusible substrate used in the present invention has a main peak position represented by 2θ of 24 ° or less, and 41 to 46 ° in addition to the main peak. There are other broad peaks in between. That is, the insoluble infusible substrate has a polyacene skeleton structure in which an aromatic polycyclic structure is appropriately developed, has an amorphous structure, and can be stably doped with lithium. Suitable as an active material.

  In the present invention, the negative electrode active material preferably has a pore diameter of 3 nm or more and a pore volume of 0.10 ml / g or more, and the upper limit of the pore diameter is not limited, but is usually in the range of 3 to 50 nm. The range of the pore volume is not particularly limited, but is usually 0.10 to 0.5 ml / g, preferably 0.15 to 0.5 ml / g.

  In the present invention, the negative electrode is formed on the negative electrode current collector from the above-mentioned carbon material or negative electrode active material powder such as PAS, but the method is not specified and a known method can be used. Specifically, the negative electrode active material powder, the binder and, if necessary, conductive powder are dispersed in an aqueous or organic solvent to form a slurry, and the slurry is applied to the current collector, or the slurry is preliminarily sheeted. It can form by shape | molding in a shape and sticking this on a collector. As the binder used here, for example, a rubber-based binder such as SBR, a synthetic fluorine-based resin such as polytetrafluoroethylene or polyvinylidene fluoride, or a thermoplastic resin such as polypropylene or polyethylene can be used. Among them, a fluorine-based binder is preferable, and it is particularly preferable to use a fluorine-based binder having a fluorine atom / carbon atom ratio (hereinafter referred to as F / C) of 0.75 or more and less than 1.5. More preferred is a fluorine-based binder of less than 1.3. Although the usage-amount of a binder changes with kinds, electrode shape, etc. of a negative electrode active material, it is 1-20 weight% with respect to a negative electrode active material, Preferably it is 2-10 weight%.

Moreover, as an electroconductive material used as needed, acetylene black, a graphite, a metal powder, etc. are mentioned. The amount of the conductive material used varies depending on the electrical conductivity of the negative electrode active material, the electrode shape, etc., but it is appropriate to add it in a proportion of 2 to 40% by weight with respect to the negative electrode active material.
In addition, the thickness of the negative electrode active material is designed with a balance of the thickness with the positive electrode active material so that the energy density of the cell can be secured, but considering the output density and energy density of the cell, industrial productivity, etc. The thickness of one side of the current collector is usually 15 to 100 μm, preferably 20 to 80 μm.

  In the LIC of the present invention, the positive electrode contains a positive electrode active material capable of reversibly holding lithium ions and / or anions such as tetrafluoroborate.

The positive electrode active material is not particularly limited as long as it can reversibly carry lithium ions and / or anions. For example, the positive electrode active material is a heat-treated product of activated carbon, conductive polymer, aromatic condensation polymer, and hydrogen atoms. Examples thereof include a polyacene organic semiconductor (PAS) having a polyacene skeleton structure having an atomic ratio of carbon atoms of 0.05 to 0.50.
The method for forming the positive electrode on the positive electrode current collector using the positive electrode active material is substantially the same as in the case of the negative electrode described above, and a detailed description thereof will be omitted.

  Further, in the LIC of the present invention, the capacitance per unit weight of the negative electrode active material has more than three times the capacitance per unit weight of the positive electrode active material, and the positive electrode active material weight is more than the negative electrode active material weight. Is also preferably large. In consideration of the capacitance of the positive electrode to be used, by appropriately controlling the filling amount (pre-doping amount) of lithium ions into the negative electrode, a capacitance more than three times the capacitance per unit weight of the positive electrode is secured, In addition, the weight of the positive electrode active material can be heavier than the weight of the negative electrode active material. Thereby, a capacitor having a higher voltage and a higher capacity than the conventional electric double layer capacitor can be obtained. Furthermore, when a negative electrode having a capacitance per unit weight larger than the capacitance per unit weight of the positive electrode is used, the negative electrode active material weight can be reduced without changing the potential change amount of the negative electrode. Therefore, the filling amount of the positive electrode active material is increased, and the capacitance and capacity of the cell can be increased. The weight of the positive electrode active material is preferably larger than the weight of the negative electrode active material, but more preferably 1.1 times to 10 times. If it is less than 1.1 times, the capacity difference becomes small, and if it exceeds 10 times, the capacity may be reduced, and the thickness difference between the positive electrode and the negative electrode becomes too large, which is not preferable in terms of the cell structure.

  As the electrolyte used in the LIC of the present invention, an electrolyte capable of transporting lithium ions is used. Such an electrolyte is preferably a liquid that can be impregnated in a separator. As the electrolyte solvent, an aprotic organic solvent capable of forming an aprotic organic solvent electrolyte solution can be preferably used. Examples of the aprotic organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, dimethoxyethane, tetrahydrofuran, dioxolane, methylene chloride, sulfolane and the like. Furthermore, a mixed solution in which two or more of these aprotic organic solvents are mixed can also be used.

As an electrolyte to be dissolved in such a solvent, any electrolyte can be used as long as it can transfer lithium ions, does not cause electrolysis even at a high voltage, and can stably exist. As such an electrolyte, lithium salts such as LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF _{6, and} Li (C ₂ F ₅ SO ₂ ) ₂ N can be preferably used.
The electrolyte and the solvent are mixed in a sufficiently dehydrated state to obtain an electrolyte solution. The electrolyte concentration in the electrolyte solution is at least 0.1 mol / l or more in order to reduce the internal resistance due to the electrolyte solution. It is preferable to make it within a range of 0.5 to 1.5 mol / l.

    Further, as the separator, a non-electrically conductive porous body having continuous vent holes that are durable against an electrolytic solution or an electrode active material can be used. Examples of the material of the separator include cellulose (paper), polyethylene, and polypropylene, and known materials can be used. Among these, cellulose (paper) is excellent in terms of durability and economy. Although the thickness of a separator is not limited, Usually, about 20-50 micrometers is preferable.

  In the LIC of the present invention, when a cell is formed by laminating two or more electrode units in the horizontal direction or the vertical direction, one of the electrode units positioned between the laminated electrode units or at both ends of the cell, or As described above, lithium metal is disposed on both outer sides as a lithium ion supply source for supporting lithium ions on the negative electrode and / or the positive electrode in advance. As the lithium metal, a substance that contains at least lithium element and can supply lithium ions, such as lithium metal or lithium-aluminum alloy, is used.

In this case, the amount of the lithium ion supply source (the weight of the substance capable of supplying lithium ions such as lithium metal) to be disposed inside the capacitor is sufficient if the amount is sufficient to obtain a predetermined negative electrode capacity. However, when a larger amount is disposed, after a predetermined amount is supported from the lithium metal, the lithium metal may be left inside the capacitor. However, in consideration of safety, it is preferable that only a necessary amount is disposed and the entire amount is supported on the negative electrode and / or the positive electrode.
In the present invention, the lithium metal is preferably formed on a lithium electrode current collector made of a conductive porous body. Here, it is preferable to use a porous metal body that does not react with a lithium ion supply source, such as a stainless mesh, as the conductive porous body serving as the lithium electrode current collector. For example, when lithium metal is used as the lithium ion supply source and a conductive porous material such as stainless steel mesh is used as the lithium electrode current collector, at least a portion of the lithium metal, preferably 80% by weight or more, is a pore of the lithium electrode current collector. It is preferably embedded in the part. Thereby, even after lithium ions are supported on the negative electrode, gaps generated between the electrodes due to the disappearance of the lithium metal are reduced, and the reliability of the LIC can be more reliably maintained.

  When lithium metal is formed on the lithium electrode current collector, the lithium metal can be formed on one or both surfaces of the porous lithium electrode current collector. The lithium metal disposed outside the electrode unit located at the end of the cell is preferably formed only on one side of the lithium electrode current collector facing the negative electrode of the electrode unit. The thickness of the lithium metal to be crimped to the lithium electrode current collector is not limited because it is appropriately determined in consideration of the amount of lithium ions supported in advance on the negative electrode, but is usually about 50 to 300 μm on one side of the lithium electrode current collector. is there.

  The material of the outer packaging container of the LIC of the present invention is not particularly limited, and various materials generally used for batteries or capacitors can be used, for example, metal materials such as iron and aluminum, plastic materials, or laminated layers thereof. Composite materials can be used. Further, the shape of the outer container is not particularly limited, and can be appropriately selected depending on the application, such as a cylindrical shape or a rectangular shape. From the viewpoint of reducing the size and weight of the LIC, a film-type exterior container using a laminate film of aluminum and a polymer material such as nylon or polypropylene is preferable.

  Hereafter, an example of the manufacturing method of LIC of this invention is shown. The through hole of the electrode collector of the LIC may or may not be blocked with a conductive material. In this example, the case of blocking will be described. The through hole of the electrode current collector can be closed by a known method such as a spray method using, for example, a carbon-based conductive material.

  Next, a positive electrode and a negative electrode are formed on the electrode current collector in which the through hole is closed with a conductive material. The positive electrode is formed by mixing a positive electrode active material with a binder resin to form a slurry, coating the positive electrode current collector, and drying. Similarly, the negative electrode is formed by mixing a negative electrode active material with a binder resin to form a slurry, coating the negative electrode current collector, and drying.

  The lithium electrode is formed by pressure bonding lithium metal onto a lithium electrode current collector made of a conductive porous body. The thickness of the lithium current collector is about 10 to 200 μm, and the thickness of the lithium metal is generally about 50 to 300 μm, although it depends on the amount of the negative electrode active material used.

After the electrode is dried, it is cut into a width that matches the size of the outer packaging container of the cell. At this time, it is preferable to cut into a shape having an extraction portion as a terminal weld portion.
Next, an electrode unit is assembled by laminating three or more layers of electrode collectors on which electrodes are formed while sandwiching a separator so that the positive electrode and the negative electrode are not in direct contact with each other. And the outside is stopped with tape. At this time, the take-out portions of the positive electrode and the negative electrode are aligned at predetermined positions.

  Lithium metal is placed on the lower and upper parts of the assembled electrode unit, and the positive electrode collector take-out part and positive electrode terminal, the negative electrode current collector and the lithium electrode current collector take-out part and negative electrode terminal are respectively ultrasonically welded. Weld.

  The electrode unit in which the above lithium metal is disposed is disposed inside the outer container, and the outer container is closed by mature fusion or the like while leaving the electrolyte inlet. At least a part of the external terminal is exposed to the outside of the outer container so that it can be connected to an external circuit. By injecting an electrolytic solution from the electrolytic solution injection port of the outer container and filling the outer container with the electrolytic solution, the electrolytic solution injection port is closed by heat fusion or the like, and the outer container is completely sealed. Lithium ion capacitor can be obtained.

  When the electrolyte is injected, all the negative electrode and lithium metal are in electrochemical contact, and the lithium ions eluted from the lithium metal into the electrolyte move to the negative electrode over time, and a predetermined amount of lithium ion is carried on the negative electrode. Is done. When supporting lithium ions on the negative electrode, the negative electrode will be deformed by strain caused by the penetration of lithium ions into the negative electrode, and restrained by applying external force so that the flatness of the negative electrode is not impaired. It is preferable to devise various ideas. In particular, in a film type battery, the contact pressure from the outer container is weaker than a battery using a metal case such as a cylindrical type or a square type battery. Therefore, by applying external pressure, the flatness of the positive electrode and the negative electrode is obtained. The distortion of the cell itself is also eliminated, and the cell performance is improved, which is preferable.

  Thus, the LIC of a preferred embodiment of the present invention uses an active material capable of reversibly supporting lithium ions and / or anions for the positive electrode, and uses an aprotic organic solvent solution of lithium salt for the electrolyte. The negative electrode is a lithium metal having a capacitance more than three times the capacitance per unit weight of the positive electrode active material, the positive electrode active material weight is larger than the negative electrode active material weight, and the lithium is previously supported on the negative electrode Is provided in the cell, and the negative electrode before charging can be previously doped with lithium ions.

  In addition, by using a negative electrode having a capacitance per unit weight that is larger than the capacitance per unit weight of the positive electrode, the weight of the negative electrode active material can be reduced without changing the potential change amount of the negative electrode. Therefore, the filling amount of the positive electrode active material is increased, and the capacitance and capacity of the cell are increased. Further, since the negative electrode has a large capacitance, the potential change amount of the negative electrode is reduced, and as a result, the potential change amount of the positive electrode is increased, and the capacitance and capacity of the cell are increased.

  Further, in the conventional electric double layer capacitor, the potential of the positive electrode drops only to about 3V at the time of discharge, but in the lithium ion capacitor of the present invention, the negative electrode potential is low, so that the positive electrode potential can be lowered to 3V or less. The capacity is higher than that of the double layer capacitor.

Furthermore, in order to obtain a required capacity as a negative electrode capacity, a predetermined amount of lithium is supported on the negative electrode in advance, so that the operating voltage of a normal capacitor is about 2.3 to 2.7 V, whereas it is 3 V or more. It can be set higher and energy density is improved.
Details will be described below with reference to specific examples.

Example 1
(Production method of negative electrode 1)
A 0.5 mm thick phenolic resin molded plate is placed in a siliconite electric furnace, heated to 500 ° C. at a rate of 50 ° C./hour, and further at a rate of 10 ° C./hour to 660 ° C. in a nitrogen atmosphere, followed by heat treatment. PAS was synthesized. The PAS plate thus obtained was pulverized with a disk mill to obtain a PAS powder. The H / C ratio of this PAS powder was 0.21.

Next, 100 parts by weight of the PAS powder and a solution prepared by dissolving 10 parts by weight of polyvinylidene fluoride powder in 80 parts by weight of N-methylpyrrolidone were sufficiently mixed to obtain a slurry. The slurry was coated on one side of a 18 μm thick copper foil so that the solid content was about 7 mg / cm ² , dried and pressed to obtain a PAS negative electrode 1.

(Method for producing positive electrode 1)
A slurry was obtained by thoroughly mixing 100 parts by weight of a commercially available specific surface area of 1950 m ² / g activated carbon powder and 10 parts by weight of polyvinylidene fluoride powder in 100 parts by weight of N-methylpyrrolidone. The slurry was applied to one surface of an aluminum foil having a thickness of 20 μm coated with a carbon-based conductive paint so that the solid content was about 7 mg / cm ² , dried, and pressed to obtain a positive electrode 1.

(Capacitance measurement per unit weight of positive electrode 1)
The positive electrode was cut into a size of 1.5 × 2.0 cm ² and used as a positive electrode for evaluation. As a positive electrode and a counter electrode, a simulation cell was assembled with a lithium metal non-woven fabric having a size of 1.5 × 2.0 cm ² and a thickness of 200 μm and a thickness of 50 μm as a separator. Metallic lithium was used as a reference electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ in propylene carbonate at a concentration of 1 mol / l was used.
The battery was charged to 3.6 V at a charging current of 1 mA and then charged at a constant voltage. After a total charging time of 1 hour, the battery was discharged to 2.5 V at 1 mA. The capacitance per unit weight of the positive electrode 1 was determined from the discharge time between 3.5 V and 2.5 V and found to be 92 F / g.

(Capacitance measurement per unit weight of negative electrode 1)
Four negative electrodes were cut into 1.5 × 2.0 cm ² sizes, and used as negative electrodes for evaluation. As a negative electrode and a counter electrode, a simulation cell was assembled with a lithium metal nonwoven fabric of 1.5 × 2.0 cm ² size and thickness of 200 μm and a polyethylene nonwoven fabric of thickness of 50 μm as a separator. Metallic lithium was used as a reference electrode. As the electrolytic solution, a solution of LiPF6 dissolved in propylene carbonate at a concentration of 1 mol / l was used.
Lithium was charged at 280 mAh / g, 350 mAh / g, 400 mAh / g, and 500 mAh / g with respect to the negative electrode active material weight at a charging current of 1 mA, and then discharged to 1.5 V at 1 mA. The electrostatic capacity per unit weight of the negative electrode 1 was determined from the discharge time during which the potential of the negative electrode changed by 0.2 V from the potential of the negative electrode one minute after the start of discharge. The results are shown in Table 1.

ここでの充電量は負極に流れた充電電流の積算値を負極活物質重量にて割った値であり、単位はｍＡｈ／ｇ。

The amount of charge here is a value obtained by dividing the integrated value of the charging current flowing through the negative electrode by the weight of the negative electrode active material, and the unit is mAh / g.

(Production method of negative electrode 2)
The slurry of the negative electrode 1 was formed on both sides of a copper expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) having a thickness of 32 μm (porosity 50%) with a die coater, and the thickness of the negative electrode as a whole after pressing (the thickness of the negative electrode layers on both sides) And the negative electrode current collector thickness) were 148 μm.

(Method for producing positive electrode 2)
A non-aqueous carbon-based conductive paint (Nippon Acheson Co., Ltd .: EB-815) is coated on both sides of an aluminum expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) with a thickness of 35 μm (porosity 50%), A positive electrode current collector having a conductive layer formed thereon was obtained by drying. The total thickness (the sum of the current collector thickness and the conductive layer thickness) was 52 μm, and the through-hole was almost blocked by the conductive paint. The positive electrode 1 slurry is formed on both sides of the positive electrode current collector with a roll coater, and the thickness of the entire positive electrode after pressing (the total thickness of the positive electrode layer on both sides, the thickness of the conductive layer on both sides, and the thickness of the positive electrode collector) ) To obtain a positive electrode 2 of 312 μm.

(Production of electrode laminate)
The negative electrode 2 with a thickness of 148 μm and the positive electrode 2 with a thickness of 312 μm are cut into 6.0 × 7.5 cm ² (excluding the terminal weld) in the shape shown in FIG. 3, and a thickness of 35 μm is used as a separator. Using a cellulose / rayon mixed nonwoven fabric, as shown in FIG. 1, the positive electrode current collector and the negative electrode current collector are arranged so that the terminal welds are on opposite sides, and the positive electrode and negative electrode facing surfaces are 20 layers. Were laminated. Separators are placed at the top and bottom and four sides are taped, and the terminal welded part (10 sheets) of the positive electrode current collector and the terminal welded part (11 sheets) of the negative electrode current collector are each 50 mm wide and long. An electrode laminate was obtained by ultrasonic welding to an aluminum positive electrode terminal and a copper negative electrode terminal having a thickness of 50 mm and a thickness of 0.2 mm. Note that 10 positive electrodes and 11 negative electrodes were used. The weight of the positive electrode active material is 1.4 times the weight of the negative electrode active material.

(Production of cell 1)
As a lithium electrode, a lithium metal foil (85 μm, 5.9 × 7.4 cm ² , equivalent to 200 mAh / g) was bonded to an 80 μm thick stainless steel mesh, and the electrode laminate was completely opposed to the negative electrode. One each was arranged on the upper part and the lower part to obtain a three-pole laminated unit. In addition, the terminal welding part (two sheets) of the lithium electrode current collector was resistance welded to the negative electrode terminal welding part. The ratio of the area facing the negative electrode of lithium metal to the negative electrode area is 97.0%.

The above tripolar laminated unit is installed inside the exterior film deeply drawn by 6.5 mm (see FIG. 1), covered with the exterior laminate film, fused on three sides, and then weighed ethylene carbonate, diethyl carbonate and propylene carbonate as electrolytes A solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / l was vacuum impregnated in a mixed solvent having a ratio of 3: 4: 1, and the remaining side was fused to assemble four cells of film type capacitors. In addition, the lithium metal arrange | positioned in a cell is equivalent to 400 mAh / g per negative electrode active material weight.

(Initial evaluation of the cell)
When one cell was disassembled after being left for 20 days after cell assembly, all the lithium metal was completely lost, so lithium was precharged to obtain a capacitance of 660 F / g per unit weight of the negative electrode active material. Judged that. The capacitance of the negative electrode is 7.2 times that of the positive electrode.

(Characteristic evaluation of cells)
The battery was charged with a constant current of 2000 mA until the cell voltage reached 3.6 V, and then a constant current-constant voltage charge in which a constant voltage of 3.6 V was applied was performed for 1 hour. Next, the battery was discharged at a constant current of 200 mA until the cell voltage reached 1.9V. This cycle of 3.6V-1.9V was repeated, and the cell capacity and energy density were evaluated in the third discharge. The results are shown in Table 2. However, the data is an average of 3 cells.

  When the positive electrode and the negative electrode were short-circuited after the measurement was completed, and the potential of the positive electrode was measured, it was 0.95 V and was 2.0 V or less. A capacitor having a high energy density was obtained by previously supporting lithium ions on the negative electrode and / or the positive electrode so that the positive electrode potential when the positive electrode and the negative electrode were short-circuited was 2.0 V or less.

(Comparative Example 1)
As a lithium electrode, a lithium metal foil (82 μm, 6.0 × 7.5 cm ² , equivalent to 200 mAh / g) is bonded to a stainless steel net having a thickness of 80 μm, and is opposed to the negative electrode by 5 mm in the width direction. Four cell capacitors were assembled in the same manner as in Example 1 except that one electrode was placed on each of the upper and lower portions of the electrode laminate to obtain a three-pole laminate unit. In addition, the lithium metal arrange | positioned in a cell is equivalent to 400 mAh / g per negative electrode active material weight.
When one cell was disassembled after being allowed to stand for 20 days after cell assembly, most of the lithium metal that had protruded without facing the negative electrode remained.
Although lithium metal remained, the battery was charged at a constant current of 2000 mA until the cell voltage reached 3.6 V, as in Example 1, and then a constant current-constant voltage charge in which a constant voltage of 3.6 V was applied was performed for 1 hour. went. Next, the battery was discharged at a constant current of 200 mA until the cell voltage reached 1.9V. This cycle of 3.6V-1.9V was repeated, and the cell capacity and energy density were evaluated in the third discharge. The results are shown in Table 3. However, the data is an average of 3 cells.

  When the positive electrode and the negative electrode were short-circuited after the measurement was completed and the potential of the positive electrode was measured, it was 1.05 V and 2.0 V or less. A capacitor having a high energy density was obtained by previously supporting lithium ions on the negative electrode and / or the positive electrode so that the positive electrode potential when the positive electrode and the negative electrode were short-circuited was 2.0 V or less. Comparative Example 1 As described above, when the lithium metal did not completely face the negative electrode, the cell capacity was smaller than that of Example 1. This seems to be because most of the lithium metal not facing the negative electrode remained, and there were not enough lithium ions to obtain the predetermined capacity of the negative electrode.

(Examples 2-4, Comparative Examples 2-4)
As a lithium metal foil, a thickness of 112 μm, vertical and horizontal size 5.5 × 6.0 cm ² (Example 2), thickness 92 μm, vertical and horizontal size 5.7 × 7.0 cm ² (Example 3), thickness 87 μm, vertical and horizontal Size 5.8 × 7.3 cm ² (Example 4), thickness 137 μm, vertical and horizontal size 4.5 × 6.0 cm ² (Comparative Example 2), thickness 185 μm, vertical and horizontal size 4.0 × 5.0 cm ² ( Comparative Example 3), 71 μm thick and 6.5 × 8.0 cm ^{2 in} length and width size (Comparative Example 4) were each crimped to a 80 μm thick stainless steel mesh, completely with the negative electrode (same as Example 1) Four film capacitors were assembled in the same manner as in Example 1 except that one each was placed on the upper and lower parts of the electrode laminate so as to face each other to obtain a three-pole laminate unit (the lithium metal in the cell was Is equivalent to 400 mAh / g). The ratios of the opposing area of the lithium metal negative electrode in Examples 2 to 4 and Comparative Examples 2 to 4 to the negative electrode area were 73.3%, 88.7%, 94.1%, 60.0%, and 44.44, respectively. 4% and 115.6%. In addition, the terminal welding part (two sheets) of the lithium electrode current collector was resistance welded to the negative electrode terminal welding part.

  When one cell was decomposed after being left for 20 days after cell assembly, Examples 3 to 5 were completely free of lithium metal, so that lithium for obtaining a capacitance of 660 F / g per unit weight of the negative electrode active material was obtained. Was precharged. Further, Comparative Examples 2 and 3 were not completely removed, and Comparative Example 4 had no portion facing the negative electrode, but the portion that did not face was left.

  As in Example 1, charging was performed at a constant current of 1000 mA until the cell voltage reached 3.6 V, and then constant current-constant voltage charging in which a constant voltage of 3.6 V was applied was performed for 1 hour. Next, the battery was discharged at a constant current of 100 mA until the cell voltage reached 1.9V. This cycle of 3.6V-1.9V was repeated, and the cell capacity and energy density were evaluated in the third discharge. The results are shown in Table 4. However, the data is an average of 3 cells.

  When the positive electrode and the negative electrode were short-circuited after the measurement was completed and the potential of the positive electrode was measured, both were 0.9 to 1.1 V and 2.0 V or less. Capacitors having a high energy density were obtained by previously supporting lithium ions on the negative electrode and / or the positive electrode so that the positive electrode potential when the positive electrode and the negative electrode were short-circuited was 2.0 V or less. It can be seen that the capacity tends to increase as the facing area increases. When the facing area is less than 70% as in Comparative Examples 2 and 3, the capacity is greatly reduced. This is considered to be because lithium metal was not completely supported and remained. In Comparative Example 4, although the facing area is large, the lithium metal protruding from the negative electrode remains, so that the capacity is considered to be low.

(Comparative Example 5)
A lithium metal foil having a thickness of 82 μm and a vertical and horizontal size of 6.0 × 7.5 cm ² bonded to a stainless steel mesh with a thickness of 80 μm is used, and the electrode is laminated so as to completely face the negative electrode (same as in Example 1). Four film capacitors were assembled in the same manner as in Example 1 except that one each was placed on the upper and lower parts of the body to obtain a three-pole laminated unit (the lithium metal in the cell was equivalent to 400 mAh / g). The ratio of the area facing the negative electrode of lithium metal to the negative electrode area is 100%. In addition, the terminal welding part (two sheets) of the lithium electrode current collector was resistance welded to the negative electrode terminal welding part.

  When one cell was disassembled after being left for 20 days after cell assembly, the lithium metal was completely lost. Therefore, it was determined that lithium was precharged to obtain a capacitance of 660 F / g per unit weight of the negative electrode active material. did.

  In the same manner as in Example 1, the battery was charged at a constant current of 2000 mA until the cell voltage reached 3.6 V, and then a constant current-constant voltage charge in which a constant voltage of 3.6 V was applied was performed for 1 hour. Next, the battery was discharged at a constant current of 200 mA until the cell voltage reached 1.9V. This cycle of 3.6V-1.9V was repeated, and the cell capacity and energy density were evaluated in the third discharge. The results are shown in Table 5. However, the data is an average of 3 cells.

  When the positive electrode and the negative electrode were short-circuited after the measurement was completed, and the potential of the positive electrode was measured, it was 0.95 V and was 2.0 V or less. A capacitor having a high energy density was obtained by previously supporting lithium ions on the negative electrode and / or the positive electrode so that the positive electrode potential when the positive electrode and the negative electrode were short-circuited was 2.0 V or less.

  When the area of the lithium metal is the same as the area of the negative electrode, that is, when the ratio of the area facing the negative electrode of the lithium metal to the negative electrode area is 100%, the negative electrode and the lithium metal are completely opposed, and the lithium metal protrudes from the negative electrode. By arranging them so that they do not exist, high capacity and high energy density were obtained as in Example 1. However, the work was difficult because lithium metal was very thin at 82 μm and it was difficult to handle. When the ratio of the area facing the negative electrode of lithium metal to the negative electrode area is 100%, workability is lowered, which is not preferable for production.

  The lithium ion capacitor of the present invention is extremely effective as a drive or auxiliary storage power source for electric vehicles, hybrid electric vehicles and the like. Further, it can be suitably used as a storage power source for driving such as an electric bicycle or an electric wheelchair, a power storage device for various energy such as solar energy or wind power generation, or a storage power source for household electric appliances.

It is sectional drawing of the lithium ion capacitor which is preferable embodiment of this invention, and shows the cross section of the AA part of FIG. The top view of FIG. It is the perspective view which notched a part of negative electrode. It is sectional drawing which shows typically the relationship between the electrode laminated body which comprises the cell of FIG. 1, and lithium metal. It is sectional drawing of the electrode laminated body concerning other embodiment of this invention. It is sectional drawing of the electrode laminated body concerning another embodiment of this invention. It is typical sectional drawing of the lithium ion capacitor which is other embodiment of this invention. It is typical sectional drawing of the lithium ion capacitor which is another embodiment of this invention.

Explanation of symbols

1: Positive electrode 1a: Positive electrode current collector 2: Negative electrode 2a: Negative electrode current collector 3: Separator 4: Lithium metal 4a: Lithium electrode current collector 5: Exterior container 6, 7: Extraction unit 8: Lithium electrode extraction unit 9: Positive electrode connection terminal 10: Negative electrode connection terminal 11: Electrode laminate 12: Hole

Claims (6)

  A positive electrode, a negative electrode, and an aprotic organic solvent solution of lithium salt as an electrolytic solution, a positive electrode active material capable of reversibly supporting lithium ions and / or anions, and a negative electrode active material reversible of lithium ions A lithium ion capacitor having a positive electrode potential of 2.0 V or less after the positive electrode and the negative electrode are short-circuited, and the positive electrode current collector and the negative electrode current collector penetrate the front and back surfaces, respectively. A lithium ion supply source provided with a hole and having a cell configuration in which a positive electrode and a negative electrode are wound through a separator, or alternately stacked three or more layers, and are disposed facing the wound or laminated negative electrode and the positive electrode; The lithium ion is supported on the negative electrode and / or the positive electrode in advance by electrochemical contact with the negative electrode and / or the positive electrode. Direction area is more than 75% of the negative electrode area, a lithium ion capacitor, which is a less than 100%.   The lithium ion capacitor according to claim 1, wherein the lithium ion supply source is disposed so as not to protrude from the negative electrode facing the lithium ion supply source.   3. The lithium ion capacitor according to claim 1, wherein when the lithium ion supply source and the negative electrode are curved, the facing area between the lithium ion supply source and the negative electrode is a projected area of each facing portion. .   2. The outermost part of an electrode laminate in which a positive electrode and a negative electrode are wound or alternately laminated via a separator is a separator, the inner side of the separator is a negative electrode, and a lithium ion supply source faces the negative electrode. 2. The lithium ion capacitor according to 2 or 3.   The negative electrode is a polyacene organic semiconductor (PAS) which is a heat-treated product of an aromatic condensation polymer and has a polyacene skeleton structure having a hydrogen atom / carbon atom ratio of 0.50 to 0.05. The lithium ion capacitor according to any one of claims 1 to 4.   The negative electrode active material has a capacitance per unit weight of at least three times that of the positive electrode active material, and the weight of the positive electrode active material is greater than the weight of the negative electrode active material. The lithium ion capacitor according to any one of 5.

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