JP2015170737A - Lithium ion capacitor, power storage device, and shovel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion capacitor which enables the suppression of the worsening of the characteristics in a low-temperature environment.SOLUTION: A lithium ion capacitor comprises: a positive electrode 10; a negative electrode 20; and a separator 40 disposed between the positive and negative electrodes. The positive electrode 10 has a structure having a positive electrode collector 11, and a positive electrode active material layer 12 formed on the positive electrode collector and including a positive electrode active material. The negative electrode 20 has a structure having a negative electrode current collector 21, and a negative electrode active material layer 22 formed on the negative electrode current collector and including a negative electrode active material. The lithium ion capacitor further comprises an electrolytic solution in contact with the positive electrode 10 and the negative electrode 20. The ratio of the mass of the negative electrode active material layer 22 to the total mass of the positive electrode active material layer 12 and the negative electrode active material layer 22 is 0.67 or larger.

Description

  The present invention relates to a lithium ion capacitor, a power storage device including the lithium ion capacitor, and a shovel equipped with the power storage device.

  As a power storage device with high energy density, a lithium ion capacitor has attracted attention. Patent Documents 1 and 2 below disclose lithium ion capacitors in which the internal resistance is reduced by optimizing the ratio between the mass of the positive electrode active material and the mass of the negative electrode active material.

Japanese Patent No. 4751199 JP 2012-195563 A

  The internal resistance of a lithium ion capacitor increases in a low temperature environment. For this reason, when a lithium ion capacitor is mounted on an excavator or the like used in a cold region, it is necessary to perform several tens of minutes of warm-up operation before work.

  The objective of this invention is providing the lithium ion capacitor which can suppress the fall of the characteristic in a low temperature environment. Another object of the present invention is to provide a power storage device including the lithium ion capacitor. Still another object of the present invention is to provide an excavator equipped with this power storage device.

According to one aspect of the invention,
At least one positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector;
At least one negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector;
A separator disposed between the positive electrode and the negative electrode;
Lithium ions having an electrolyte solution in contact with the positive electrode and the negative electrode, wherein the ratio of the mass of the negative electrode active material layer to the total mass of the positive electrode active material layer and the negative electrode active material layer is 0.67 or more A capacitor is provided.

According to another aspect of the invention,
A plurality of plate-like lithium ion capacitors stacked in the thickness direction;
A pressure mechanism for applying a compressive force in the stacking direction to the laminate of the lithium ion capacitors;
A housing for housing the lithium ion capacitor and the pressure mechanism;
Each of the lithium ion capacitors is provided with a power storage device having the above-described configuration.

According to yet another aspect of the invention,
A lower traveling body,
An upper swing body mounted so as to be swingable with respect to the lower traveling body;
An attachment including a boom and an arm attached to the upper swing body;
An electric motor for turning the upper turning body;
A power storage device for supplying electric power to the electric motor,
The power storage device is provided with an excavator having the above-described configuration.

  When the ratio of the mass of the negative electrode active material layer to the total mass of the positive electrode active material layer and the negative electrode active material layer is 0.67 or more, deterioration of impedance characteristics in a low temperature environment can be suppressed.

1A is a plan view of a lithium ion capacitor according to an embodiment, and FIG. 1B is a cross-sectional view taken along one-dot chain line 1B-1B in FIG. 1A. FIG. 2 is a graph showing the relationship between the capacitance C of the lithium ion capacitor and the masses Wc and Wa of the positive electrode active material layer and the negative electrode active material layer. 3A and 3B are graphs showing AC impedance characteristics of the lithium ion capacitor at temperatures of 30 ° C. and 0 ° C., respectively. 4A and 4B are schematic cross-sectional views of a lithium ion capacitor according to an example manufactured for evaluating impedance characteristics. 5A and 5B are graphs showing measurement results of resistance and reactance temperature characteristics of a sample using hard carbon as a negative electrode active material, respectively. 6A and 6B are graphs showing measurement results of resistance and reactance temperature characteristics of a sample using graphite as a negative electrode active material, respectively. 7A is a plan view of a lithium ion capacitor according to another embodiment, and FIG. 7B is a cross-sectional view taken along one-dot chain line 7B-7B in FIG. 7A. 8A to 8C are cross-sectional views of three types of configuration examples of the electrode stack. 9A and 9B are perspective views of a lid and a lower housing of the power storage device according to the embodiment, respectively. FIG. 10 is a plan view of a lower housing of the power storage device according to the embodiment and components mounted on the lower housing. 11A is a plan view of a power storage module of the power storage device according to the embodiment, and FIG. 11B is a cross-sectional view taken along one-dot chain line 11B-11B in FIG. 11A. FIG. 12 is a side view of an excavator on which the power storage device according to the embodiment is mounted. FIG. 13 is a block diagram of an excavator on which the power storage device according to the embodiment is mounted.

  FIG. 1A shows a plan view of a lithium ion capacitor according to an embodiment. FIG. 1B is a cross-sectional view taken along one-dot chain line 1B-1B in FIG. 1A. A reference electrode 30, a separator 40, a negative electrode (anode) 20, a separator 40, a positive electrode (cathode) 10, a separator 40, and a reference electrode 30 are sequentially stacked to constitute an electrode laminate 42. The electrode laminate 42 is accommodated in a cell container 50 made of a laminate film or the like. The cell container 50 is filled with an electrolytic solution. The electrolytic solution is impregnated in the separator 40 and contacts the positive electrode 10 and the negative electrode 20.

  The positive electrode 10 includes a positive electrode current collector 11 and a positive electrode active material layer 12. The negative electrode 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22. The reference electrode 30 includes a reference electrode current collector 31 and a lithium foil 32. A positive electrode tab 15 extends from the positive electrode current collector 11 to the outside of the cell container 50. A negative electrode tab 25 extends from the negative electrode current collector 21 to the outside of the cell container 50. A reference electrode tab 35 extends from the reference electrode current collector 31 to the outside of the cell container 50.

Next, a method for manufacturing a lithium ion capacitor will be described. A slurry made of a positive electrode active material, a conductive additive, a binder, and a thickener is applied to an aluminum foil having a thickness of about 30 μm roughened by etching. For example, activated carbon is used as the positive electrode active material. After applying slurry to the aluminum foil, it is dried under reduced pressure. The positive electrode active material layer 12 containing a positive electrode active material is formed by drying under reduced pressure. The aluminum foil is cut so that the portion where the positive electrode active material layer 12 is formed is a 30 cm × 30 cm square. Thereby, the positive electrode 10 in which the positive electrode active material layer 12 is formed on the positive electrode current collector 11 made of aluminum foil is produced. At the time of cutting, the positive electrode tab 15 made of an aluminum foil in a region where the positive electrode active material layer 12 is not formed is also cut out at the same time.

  A slurry composed of a negative electrode active material, a conductive additive, a binder, and a thickener is applied to an electrolytic copper foil having a thickness of about 10 to 15 μm. As the negative electrode active material, for example, artificial graphite, hard carbon or the like is used. After applying slurry to the electrolytic copper foil, it is dried under reduced pressure. The negative electrode active material layer 22 containing a negative electrode active material is formed by drying under reduced pressure. The electrolytic copper foil is cut so that the portion where the negative electrode active material layer 22 is formed is a 30 cm × 30 cm square. Thereby, the negative electrode 20 in which the negative electrode active material layer 22 is formed on the negative electrode current collector 21 made of electrolytic copper foil is produced. At the time of cutting, a negative electrode tab 25 made of an electrolytic copper foil in a region where the negative electrode active material layer 22 is not formed is cut out at the same time.

  A lithium foil 32 is rolled and bonded to a reference electrode current collector 31 made of a copper foil. The reference electrode 30 is produced by cutting the copper foil. At the time of cutting, the reference electrode tab 35 is also cut out at the same time.

  The electrode stack 42 is formed by stacking the separator 40, the negative electrode 20, the separator 40, the positive electrode 10, the separator 40, and the reference electrode 30 on the reference electrode 30. At this time, the positive electrode 10 and the negative electrode 20 are arranged so that the positive electrode active material layer 12 of the positive electrode 10 and the negative electrode active material layer 22 of the negative electrode 20 face each other. The reference electrode 30 is disposed so that the lithium foil 32 faces the negative electrode 20 or the positive electrode 10. For the separator 40, for example, a nonwoven fabric made of cellulose or a microporous film is used. The electrode laminate 42 is sandwiched between laminate films and the periphery is thermally welded. At this stage, the cell container 50 whose peripheral part is open is manufactured.

After injecting the electrolyte into the cell container 50, the open part of the cell container 50 is sealed. As the electrolytic solution, for example, a lithium salt dissolved in an organic solvent is used. For example, LiPF ₆ is used as the lithium salt. As the organic solvent, a mixed liquid of ethylene carbonate and dimethyl carbonate is used.

Next, a general method for determining the mass of the positive electrode active material layer 12 and the negative electrode active material layer 22 will be described with reference to FIG. The electrostatic capacity of the lithium ion capacitor is represented by an equivalent circuit in which a positive electrode capacity and a negative electrode capacity are connected in series. The positive electrode capacity is represented by the product of the capacity Cc per unit mass of the positive electrode active material layer 12 (hereinafter referred to as positive electrode unit capacity) and the mass Wc of the positive electrode active material layer 12. The negative electrode capacity is represented by the product of the capacity Ca per unit mass of the negative electrode active material layer 22 (hereinafter referred to as negative electrode unit capacity) and the mass Wa of the negative electrode active material layer 22. Therefore, when the electrostatic capacity of the lithium ion capacitor per unit mass of the positive electrode active material layer 12 and the negative electrode active material layer 22 is represented by C, the following equation is established.
1 / (C × (Wa + Wc)) = 1 / (Ca × Wa) + 1 / (Cc × Wc)

FIG. 2 shows the relationship between the electrostatic capacity C of the lithium ion capacitor and the masses Wc and Wa of the positive electrode active material layer 12 and the negative electrode active material layer 22. The horizontal axis represents the ratio of the mass Wc of the positive electrode active material layer 12 to the total of the mass Wc of the positive electrode active material layer 12 and the mass Wa of the negative electrode active material layer 22. The vertical axis represents the capacitance C ₀ when the mass Wc of the positive electrode active material layer 12 and the mass Wa of the negative electrode active material layer 22 are equal and the positive electrode unit capacity Cc and the negative electrode unit capacity Ca are equal. Represents the standardized capacitance C / C ₀ of the lithium ion capacitor. A structure in which the positive electrode unit capacitance Cc and the negative electrode unit capacitance Ca are equal corresponds to an electric double layer capacitor. In the lithium ion capacitor, the negative electrode unit capacity Ca is larger than the positive electrode unit capacity Cc.

In FIG. 2, rhombus, square, triangle, and circle symbols indicate normalized capacitance C / C ₀ when Ca / Cc = 1, 10, 20, and 200, respectively. In the electric double layer capacitor, the normalized capacitance C / C ₀ becomes the maximum value 1 when the positive electrode active material layer mass ratio Wc / (Wc + Wa) = 0.5. In the lithium ion capacitor, it can be seen that a large capacitance C is obtained when the positive electrode active material layer mass ratio Wc / (Wc + Wa) is in the range of 0.7 to 0.9.

  However, it has been found that the preferable range of the positive electrode active material layer mass ratio Wc / (Wc + Wa) for obtaining a large capacitance C is not suitable as a power storage device for a work machine such as an excavator. Hereinafter, the preferable range of the positive electrode active material layer mass ratio of the lithium ion capacitor mounted on a work machine such as an excavator will be described.

  3A and 3B show AC impedance characteristics of the lithium ion capacitor at temperatures of 30 ° C. and 0 ° C., respectively. The horizontal axis represents the real part (resistance) of the impedance in the unit “Ω”, and the vertical axis represents the imaginary part (reactance) of the impedance in the unit “Ω”. The AC impedance was measured by setting the amplitude of the applied voltage to 10 mV and changing the measurement frequency within the range of 0.1 Hz to 1 MHz. The thin solid line in FIGS. 3A and 3B shows the impedance (impedance of the entire cell) between the positive electrode 10 and the negative electrode 20 (FIG. 1B), and the broken line between the positive electrode 10 and the reference electrode 30 (FIG. 1B). The impedance (positive electrode impedance) is shown, and the thick solid line shows the impedance (negative electrode impedance) between the negative electrode 20 and the reference electrode 30 (FIG. 1B). In any graph, the end far from the origin corresponds to the impedance when the measurement frequency is 0.1 Hz, and the end near the origin corresponds to the impedance when the measurement frequency is 1 MHz.

  As shown in FIGS. 3A and 3B, at a temperature of 30 ° C., the resistance of the positive electrode is higher than the resistance of the negative electrode. However, when the temperature drops to 0 ° C., the resistance of the positive electrode hardly increases, but the resistance of the negative electrode increases significantly. It can be seen that the decrease in the impedance characteristics of the lithium ion capacitor in a low temperature environment is caused by an increase in the resistance of the negative electrode. From the evaluation results shown in FIGS. 3A and 3B, it is considered that the increase in resistance of the negative electrode may be suppressed in order to suppress the deterioration of the characteristics of the lithium ion capacitor in a low temperature environment.

  The inventor of the present application thought that the increase in the resistance of the negative electrode in a low temperature environment could be suppressed by increasing the amount of the negative electrode active material. In order to confirm this hypothesis, a sample in which the mass of the negative electrode active material was increased was prepared, and the impedance characteristics were evaluated.

  4A and 4B are schematic cross-sectional views of the sample for evaluation. Hereinafter, differences from the lithium ion capacitor illustrated in FIG. 1B will be described. In the lithium ion capacitor illustrated in FIG. 1B, the negative electrode active material layer 22 is formed only on one surface of the negative electrode current collector 21.

  In the sample shown in FIG. 4A, negative electrode active material layers 22 are formed on both surfaces of the negative electrode current collector 21. The mass of each of the negative electrode active material layers 22 is the same as the mass of the negative electrode active material layer 22 illustrated in FIG. 1B. For this reason, the mass of the negative electrode active material layer 22 of the sample shown in FIG. 4A is twice the mass of the negative electrode active material layer 22 of the lithium ion capacitor shown in FIG. 1B.

In the sample shown in FIG. 4B, two negative electrodes 20 each having a negative electrode active material layer 22 formed on both surfaces of the negative electrode current collector 21 are arranged. For this reason, the mass of the negative electrode active material layer 22 of the sample shown in FIG. 4B is four times the mass of the negative electrode active material layer 22 of the lithium ion capacitor shown in FIG. 1B. One negative electrode current collector 21 is welded to the other negative electrode current collector 21. Only one negative electrode current collector 21 is led out to the outside of the cell container 50.

  FIG. 5A and FIG. 5B show measurement results of resistance and capacitance temperature characteristics of a sample using hard carbon as a negative electrode active material, respectively. The horizontal axis of FIGS. 5A and 5B represents temperature in units of “° C.”, the vertical axis of FIG. 5A represents resistance in units of “Ω”, and the vertical axis of FIG. 5B represents capacitance in units of “F”. Squares, circles, and triangles in the figure correspond to samples having the structures shown in FIGS. 1B, 4A, and 4B, respectively. The negative electrode active material layer mass ratios Wa / (Wc + Wa) of the samples indicated by squares, circles, and triangles are 0.66, 0.80, and 0.89, respectively.

  Resistance and capacitance were calculated from charge / discharge characteristics measured by repeating constant current / low voltage charge and constant current discharge five times. More specifically, the resistance was calculated from the amount of voltage drop caused by the internal resistance at the start of discharge. The capacitance was calculated from the amount of discharge energy obtained from the time change of voltage.

  As shown in FIG. 5A, the resistance increases as the temperature decreases. In the region where the temperature is lower than 20 ° C., the difference in resistance of each sample widens. It can be seen that the larger the negative electrode active material layer mass ratio, the smaller the increase in resistance when the temperature is lowered.

  As shown in FIG. 5B, the capacitance is not easily affected by temperature changes, and no significant difference in capacitance is seen among the three samples.

  From the evaluation results shown in FIG. 5A and FIG. 5B, the negative electrode active material layer mass ratio Wa / (Wc + Wa) is preferably set to 0.67 or more in order to suppress deterioration of impedance characteristics at low temperatures, It is derived that the above is more preferable. In addition, it was confirmed that good impedance characteristics at low temperatures can be obtained when the negative electrode active material layer mass ratio Wa / (Wc + Wa) is 0.89 or less.

  FIG. 6A and FIG. 6B show measurement results of resistance and capacitance temperature characteristics of a sample using graphite as a negative electrode active material, respectively. 6A and 6B, the horizontal axis represents temperature in units of “° C.”, the vertical axis in FIG. 6A represents resistance in units of “Ω”, and the vertical axis in FIG. 6B represents capacitance in units of “F”. In the sample using graphite as the negative electrode active material, the negative electrode active material layer mass ratio Wa / (Wc + Wa) was changed by adjusting the thickness of the negative electrode active material layer 22 (FIG. 1B). The triangle and square symbols in the figure correspond to samples having negative electrode active material layer mass ratios Wa / (Wc + Wa) of 0.46 and 0.67, respectively.

  As shown in FIG. 6A, even when graphite is used as the negative electrode active material, it can be seen that the sample having a larger mass of the negative electrode active material layer has lower resistance at low temperatures. Also, there is no significant difference in capacitance between the two samples. Even when graphite is used for the negative electrode active material, it is considered that an increase in resistance at a low temperature can be suppressed by setting the negative electrode active material layer mass ratio Wa / (Wc + Wa) to 0.67 or more.

From the graph shown in FIG. 2, when the negative electrode active material layer mass ratio Wa / (Wc + Wa) is 0.67 or more, that is, Wc / (Wc + Wa) is 0.33 or less, the normalized capacitance C is smaller than 1. turn into. Thus, when the negative electrode active material layer mass ratio Wa / (Wc + Wa) is 0.67 or more, an advantageous effect cannot be obtained in terms of the capacitance per unit mass of the active material. However, for applications where it is desired to suppress an increase in resistance at low temperatures, a sufficient effect is obtained in which the mass ratio of the negative electrode active material layer is in the above range. For example, by adopting a lithium ion capacitor having the above-mentioned negative electrode active material layer mass ratio to a shovel or the like operating in a cold region,
The warm-up time can be shortened and the operating efficiency can be increased.

  FIG. 7A shows a plan view of a lithium ion capacitor according to another embodiment. A positive electrode tab 15 and a negative electrode tab 25 are drawn out from two edges of the cell container 50 having a substantially rectangular planar shape on opposite sides.

  FIG. 7B is a cross-sectional view taken along one-dot chain line 7B-7B in FIG. 7A. A cell container 50 is constituted by two laminated films 50A and 50B. The laminate films 50A and 50B sandwich the electrode laminate 42 and seal the electrode laminate 42. The electrode laminate 42 includes positive electrodes 10 and negative electrodes 20 that are alternately laminated. The positive electrode 10 and the negative electrode 20 are insulated by a separator 40 disposed between them. The detailed structure of the electrode laminate 42 will be described later with reference to FIGS. 8A to 8C.

  One laminate film 50B is substantially flat, and the other laminate film 50A is deformed to reflect the shape of the electrode laminate 42.

  Each of the positive electrode 10 and the negative electrode 20 has connection portions 10A and 20A that extend in the opposite directions (leftward and rightward in FIG. 7A) from their overlapping regions. Connection portions 10 </ b> A of the plurality of positive electrodes 10 are overlapped and welded to the positive electrode tab 15. The connecting portions 20 </ b> A of the plurality of negative electrodes 20 are overlapped and welded to the negative electrode tab 25. For the positive electrode tab 15 and the negative electrode tab 25, for example, an aluminum plate or a copper plate is used.

  The positive electrode tab 15 and the negative electrode tab 25 are led out to the outside of the cell container 50 through between the laminate film 50A and the laminate film 50B. The positive electrode tab 15 and the negative electrode tab 25 are thermally welded to the laminate film 50A and the laminate film 50B at the lead-out location.

  A gas vent valve 26 is disposed between the connecting portion 10A of the positive electrode 10 and the laminate film 50A. The gas vent valve 26 is disposed so as to close the gas vent hole 27 formed in the laminate film 50A, and is thermally welded to the laminate film 50A. The gas generated in the cell container 50 is discharged to the outside through the gas vent valve 26 and the gas vent hole 27. The cell container 50 is evacuated. For this reason, the laminate films 50 </ b> A and 50 </ b> B are deformed so as to follow the outer shapes of the electrode laminate 42 and the gas vent valve 26 due to atmospheric pressure.

  8A to 8C are cross-sectional views of three types of configuration examples of the electrode laminate 42, respectively. In the configuration example shown in FIG. 8A, the positive electrode active material layer 12 is formed only on one surface of the positive electrode current collector 11, and the negative electrode active material layer 22 is formed on both surfaces of the negative electrode current collector 21. Thereby, the mass of the negative electrode active material layer 22 and the mass of the positive electrode active material layer 12 are adjusted.

  In the configuration example shown in FIG. 8B, the positive electrode active material layers 12 are formed on both surfaces of the positive electrode current collector 11, and the negative electrode active material layers 22 are formed on both surfaces of the negative electrode current collector 21. The negative electrode active material layer 22 is thicker than the positive electrode active material layer 12. Thus, by adjusting the thicknesses of the positive electrode active material layer 12 and the negative electrode active material layer 22, the mass of the negative electrode active material layer 22 and the mass of the positive electrode active material layer 12 are adjusted.

  In the configuration example shown in FIG. 8C, the positive electrode active material layer 12 and the negative electrode active material layer 22 have substantially the same thickness. Two negative electrodes 20 are arranged for one positive electrode 10. Specifically, two negative electrodes 20 are disposed between the positive electrodes 10. Three or more negative electrodes 20 may be arranged for one positive electrode 10. Thus, by adjusting the number of the negative electrodes 20, the mass of the negative electrode active material layer 22 and the mass of the positive electrode active material layer 12 are adjusted.

  8A to 8C, the negative electrode active material layer mass ratio Wa / (Wc + Wa) is adjusted to 0.67 or more, more preferably 0.8 or more. Further, the negative electrode active material layer mass ratio Wa / (Wc + Wa) is adjusted to 0.89 or less.

  9A and 9B are perspective views of a lid 60 and a lower housing 70 of a power storage device according to another embodiment, respectively. As shown in FIG. 9B, the lower housing 70 includes a bottom surface 71 and a side surface 72, and an opening is provided above. The side surface 72 is disposed over the entire outer peripheral line of the bottom surface 71. 9A closes the opening of the lower housing 70. The lid 60 shown in FIG.

  Two power storage modules 73 are mounted on the bottom surface 71. An xyz orthogonal coordinate system in which a plane parallel to the bottom surface 71 is defined as an xy plane and a normal direction of the bottom surface 71 is defined as a z direction is defined. The direction in which the two power storage modules 73 are separated is the x direction. Each of the power storage modules 73 includes a plurality of power storage cells stacked in the y direction, and charges and discharges electrical energy. Each of the storage cells uses a lithium ion capacitor according to any of the embodiments shown in FIGS. 7A to 7B and FIGS. 8A to 8C. The detailed configuration of the power storage module 73 will be described later with reference to FIGS. 11A and 11B.

  A connector box 79 is provided on one side surface 72 perpendicular to the y direction. The space in the connector box 79 and the space in the lower housing 70 communicate with each other through the opening 78. The opening above the connector box 79 is closed with a connector plate on which connector terminals are arranged.

  A first rib 75, a second rib 76, and a third rib 77 for increasing rigidity are formed on the bottom surface 71. The first rib 75 is disposed between the two power storage modules 73 and extends in a direction intersecting the x direction (y direction). One end of the first rib 75 is continuous with the side surface 72 opposite to the side surface 72 where the connector box 79 is provided.

  The second rib 76 is continuous with the first rib 75 and extends in the x direction. The first rib 75 is connected to the center of the second rib 76. The third rib 77 extends in the y direction from both ends of the second rib 76 and reaches the side surface 72 where the connector box 79 is provided. The opening 78 is formed between the locations where the two third ribs 77 are connected to the side surface 72.

  With reference to the bottom surface 71, the first rib 75, the second rib 76, and the third rib 77 are lower than the side surface 72. With the opening of the lower housing 70 closed by the lid 60, the first rib 75 and the lid 60, the second rib 76 and the lid 60, and the third rib 77 and the lid 60 A gap is formed between the two.

  The bottom surface 71, the side surface 72, the first rib 75, the second rib 76, the third rib 77, and the connector box 79 are integrally formed by a casting method. For example, aluminum is used as the material.

  FIG. 10 is a plan view of the lower housing 70 and components mounted on the lower housing 70. Two power storage modules 73 are mounted apart in the x direction. The first rib 75 passes in the y direction between the regions where the two power storage modules 73 are mounted. One end of the first rib 75 is continuous with the side surface 72. The other end of the first rib 75 is located outside the end of the power storage module 73 in the y direction. From this end, the second rib 76 extends in the x direction. The second rib 76 partially overlaps each of the power storage modules 73 in the x direction. From both ends of the second rib 76, the third rib 77 extends in the y direction and reaches the side surface 72 where the connector box 79 is provided.

  A pair of relay members 82 are arranged in a region surrounded by the second rib 76, the third rib 77, and the connector box 79. A relay circuit 83 is disposed in the connector box 79. That is, the relay circuit 83 is mounted at a position away from the power storage module 73 in the y direction.

  Each of the power storage modules 73 has terminals 81 at both ends in the y direction. The storage module 73 is charged and discharged through the terminal 81. Terminals 81 far from the connector box 79 are electrically connected to each other via an electric circuit component 84 including a fuse, a safety switch, and the like.

  Terminals 81 closer to the connector box 79 are electrically connected to the relay member 82 by bus bars 85, respectively. The bus bar 85 intersects with the second rib 76. The relay member 82 is connected to the relay circuit 83 by the bus bar 86. Bus bar 86 passes through opening 78 (FIG. 1B).

  FIG. 11A shows a plan view of the power storage module 73. Plate-shaped storage cells 90 and heat transfer plates 91 are alternately stacked in the thickness direction (y direction). A single heat transfer plate 91 may be arranged for a plurality of, for example, two storage cells 90. A pair of electrode tabs 92 are drawn out from each of the storage cells 90. The pair of electrode tabs 92 are drawn out in the x direction and in opposite directions. A plurality of energy storage cells 90 are connected in series by connecting the electrode tabs 92 of the energy storage cells 90 adjacent to each other. The electrode tabs 92 of the storage cells 90 at both ends are connected to the two terminals 81 of the storage module 73, respectively.

  The pressurizing mechanism 96 applies a compressive force in the stacking direction to the stacked structure in which the storage cells 90 and the heat transfer plates 91 are stacked. The pressure mechanism 96 includes a pressure plate 93 disposed at both ends of the laminated structure, and a plurality of tie rods 94 extending from one pressure plate 93 to the other pressure plate 93. By tightening the tie rod 94 with a nut, a compressive force in the stacking direction can be applied to the stacked structure of the storage cell 90 and the heat transfer plate 91.

  FIG. 11B is a cross-sectional view taken along one-dot chain line 11B-11B in FIG. 11A. A pressure plate 93 is screwed to the bottom surface 71 of the lower housing 70. The lower end of the heat transfer plate 91 is in contact with the bottom surface 71, and the upper end is in contact with the lid 60. The lid 60 is fastened and fixed to the lower housing 70 with bolts or the like, and a compressive force in the z direction is applied to the heat transfer plate 91. Due to this compressive force, the power storage module 73 is firmly and non-slidably fixed in the housing composed of the lower housing 70 (FIG. 9B) and the lid 60 (FIG. 9A).

  A cooling medium flow path 95 is formed in the bottom surface 71, and a cooling medium flow path 65 is also formed in the lid 60. The storage medium 90 can be cooled via the heat transfer plate 91 by circulating a cooling medium such as cooling water through the flow paths 95 and 65.

  FIG. 12 shows a side view of an excavator equipped with the power storage device according to the embodiment. An upper turning body 101 is mounted on the lower traveling body 100 so as to be turnable. An attachment including a boom 103, an arm 105, and a bucket 107 is connected to the upper swing body 101. As the boom cylinder 104 expands and contracts, the posture of the boom 103 changes. As the arm cylinder 106 expands and contracts, the posture of the arm 105 changes. Due to the expansion and contraction of the bucket cylinder 108, the posture of the bucket 107 changes. The boom cylinder 104, the arm cylinder 106, and the bucket cylinder 108 are hydraulically driven. A swivel motor 102, an engine 110, a motor generator 111, and a power storage device 115 are mounted on an excavator body, specifically, an upper swing body 101.

  FIG. 13 shows a block diagram of the excavator. In FIG. 13, the mechanical power system is represented by a double line, the high-pressure hydraulic line is represented by a thick solid line, the electric control system is represented by a thin solid line, and the pilot line is represented by a broken line.

  The drive shaft of engine 110 is connected to the input shaft of torque transmission mechanism 121. The engine 110 is an engine that generates a driving force using fuel other than electricity, for example, an internal combustion engine such as a diesel engine.

  The drive shaft of the motor generator 111 is connected to the other input shaft of the torque transmission mechanism 121. The motor generator 111 can perform both the electric (assist) operation and the power generation operation. The torque transmission mechanism 121 has two input shafts and one output shaft. A drive shaft of the main pump 122 is connected to the output shaft.

  When the load applied to the main pump 122 is large, the motor generator 111 performs an assist operation, and the driving force of the motor generator 111 is transmitted to the main pump 122 via the torque transmission mechanism 121. Thereby, the load applied to the engine 110 is reduced. On the other hand, when the load applied to the main pump 122 is small, the driving force of the engine 110 is transmitted to the motor generator 111 via the torque transmission mechanism 121, so that the motor generator 111 is operated for power generation.

  The main pump 122 supplies hydraulic pressure to the control valve 124 via the high pressure hydraulic line 123. The control valve 124 distributes hydraulic pressure to the hydraulic motors 109 </ b> A and 109 </ b> B, the boom cylinder 104, the arm cylinder 106, and the bucket cylinder 108 according to a command from the driver. The hydraulic motors 109A and 109B drive two left and right crawlers provided in the lower traveling body 100 (FIG. 12), respectively.

  Motor generator 111 is connected to power storage circuit 112 via inverter 113A. The turning electric motor 102 is connected to the power storage circuit 112 via the inverter 113B. Inverters 113 </ b> A and 113 </ b> B and power storage circuit 112 are controlled by control device 135.

  Inverter 113 </ b> A controls operation of motor generator 111 based on a command from control device 135. Switching between the assist operation and the power generation operation of the motor generator 111 is performed by the inverter 113A.

  During the period in which the motor generator 111 is assisted, necessary power is supplied from the power storage circuit 112 to the motor generator 111 through the inverter 113A. During the period in which the motor generator 111 is generating, the electric power generated by the motor generator 111 is supplied to the power storage circuit 112 through the inverter 113A. Thereby, power storage device 115 in power storage circuit 112 is charged. The power storage device 115 in the power storage circuit 112 uses the power storage device according to the embodiment shown in FIGS. 9A to 11B.

  The swing electric motor 102 is AC driven by the inverter 113B and can perform both the power running operation and the regenerative operation. During the power running operation of the swing motor 102, electric power is supplied from the power storage circuit 112 to the swing motor 102 via the inverter 113B. The turning electric motor 102 turns the upper turning body 101 (FIG. 12) through the speed reducer 131. During the regenerative operation, the rotational motion of the upper swing body 101 is transmitted to the swing motor 102 via the speed reducer 131, so that the swing motor 102 generates regenerative power. The generated regenerative power is supplied to the power storage circuit 112 via the inverter 113B. Thereby, power storage device 115 in power storage circuit 112 is charged.

  The resolver 132 detects the position of the rotating shaft of the turning electric motor 102 in the rotation direction. The detection result of the resolver 132 is input to the control device 135. By detecting the position of the rotating shaft in the rotational direction before and after the operation of the turning electric motor 102, the turning angle and the turning direction are derived.

  A mechanical brake 133 is connected to the rotating shaft of the turning electric motor 102 and generates a mechanical braking force. The braking state and the release state of the mechanical brake 133 are controlled by the control device 135 and are switched by an electromagnetic switch.

  The pilot pump 125 generates a pilot pressure necessary for the hydraulic operation system. The generated pilot pressure is supplied to the operating device 128 via the pilot line 126. The operation device 128 includes a lever and a pedal and is operated by a driver. The operating device 128 converts the primary side hydraulic pressure supplied from the pilot line 126 into a secondary side hydraulic pressure in accordance with the operation of the driver. The secondary hydraulic pressure is transmitted to the control valve 124 via the hydraulic line 129 and also to the pressure sensor 127 via the other hydraulic line 130.

  The pressure detection result detected by the pressure sensor 127 is input to the control device 135. Thereby, the control apparatus 135 can detect the operation state of the lower traveling body 100, the turning electric motor 102, the boom 103, the arm 105, and the bucket 107 (FIG. 12).

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

DESCRIPTION OF SYMBOLS 10 Positive electrode 10A Connection part 11 Positive electrode collector 12 Positive electrode active material 15 Positive electrode tab 20 Negative electrode 20A Connection part 21 Negative electrode collector 22 Negative electrode active material 25 Negative electrode tab 26 Degassing valve 27 Degassing hole 30 Reference electrode 31 Reference electrode current collector Body 32 Lithium foil 35 Reference electrode tab 40 Separator 42 Electrode stack 50 Cell container 50A, 50B Laminate film 60 Lid 70 Lower housing 71 Bottom surface 72 Side surface 73 Power storage module 75 First rib 76 Second rib 77 Third rib 78 Opening 79 Connector box 81 Terminal 82 Relay member 83 Relay circuit 84 Electrical circuit component 85, 86 Bus bar 90 Power storage cell 91 Heat transfer plate 92 Electrode tab 93 Pressure plate 94 Tie rod 95 Channel 96 Pressure mechanism 100 Lower traveling body 101 Upper part turning Body 102 Electric motor 103 Boom 104 Boom cylinder 105 Arm 06 Arm cylinder 107 Bucket 108 Bucket cylinder 109A Hydraulic motor 109B Hydraulic motor 110 Engine 111 Motor generator 112 Power storage circuit 113A Inverter 113B Inverter 115 Power storage device 121 Torque transmission mechanism 122 Main pump 123 High pressure hydraulic line 124 Control valve 125 Pilot pump 126 Pilot line 127 Pressure sensor 128 Operating device 129, 130 Hydraulic line 131 Reducer 132 Resolver 133 Mechanical brake 135 Control device

Claims (11)

At least one positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector;
At least one negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector;
A separator disposed between the positive electrode and the negative electrode;
Lithium ions having an electrolyte solution in contact with the positive electrode and the negative electrode, wherein the ratio of the mass of the negative electrode active material layer to the total mass of the positive electrode active material layer and the negative electrode active material layer is 0.67 or more Capacitor.   2. The lithium ion capacitor according to claim 1, wherein a ratio of a mass of the negative electrode active material layer to a total mass of the positive electrode active material layer and the negative electrode active material layer is 0.89 or less.   The lithium ion capacitor according to claim 1, wherein the positive electrode active material is activated carbon, and the negative electrode active material is graphite or hard carbon.   The lithium ion capacitor according to claim 1, wherein the negative electrode active material layer is thicker than the positive electrode active material layer.   The lithium ion capacitor according to any one of claims 1 to 3, wherein a plurality of the negative electrodes are arranged with respect to one positive electrode. A plurality of plate-like lithium ion capacitors stacked in the thickness direction;
A pressure mechanism for applying a compressive force in the stacking direction to the laminate of the lithium ion capacitors;
A housing for housing the lithium ion capacitor and the pressure mechanism;
Each of the lithium ion capacitors is
At least one positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector;
At least one negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector;
A separator disposed between the positive electrode and the negative electrode;
A power storage device having an electrolyte solution in contact with the positive electrode and the negative electrode, wherein a ratio of a mass of the negative electrode active material layer to a total mass of the positive electrode active material layer and the negative electrode active material layer is 0.67 or more .   The power storage device according to claim 6, wherein a ratio of a mass of the negative electrode active material layer to a total mass of the positive electrode active material layer and the negative electrode active material layer is 0.89 or less.   The power storage device according to claim 6 or 7, wherein the positive electrode active material is activated carbon, and the negative electrode active material is graphite or hard carbon.   The power storage device according to claim 6, wherein the negative electrode active material layer is thicker than the positive electrode active material layer.   The power storage device according to any one of claims 6 to 8, wherein a plurality of the negative electrodes are arranged for one positive electrode. A lower traveling body,
An upper swing body mounted so as to be swingable with respect to the lower traveling body;
An attachment including a boom and an arm attached to the upper swing body;
An electric motor for turning the upper turning body;
A power storage device for supplying electric power to the electric motor,
The power storage device
A plurality of plate-like lithium ion capacitors stacked in the thickness direction;
A pressure mechanism for applying a compressive force in the stacking direction to the laminate of the lithium ion capacitors;
A housing for housing the lithium ion capacitor and the pressure mechanism;
Each of the lithium ion capacitors is
At least one positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector;
At least one negative electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector;
A separator disposed between the positive electrode and the negative electrode;
An excavator having an electrolyte solution in contact with the positive electrode and the negative electrode, wherein a ratio of a mass of the negative electrode active material layer to a total mass of the positive electrode active material layer and the negative electrode active material layer is 0.67 or more.

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