JP2012023889A - Electrical power system and vehicle using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight and small electrical power system that satisfies specified output density and energy density and requires no heat radiator for a capacitor, and a vehicle using the same.SOLUTION: An electrical power system 45 comprises: a lithium ion capacitor 20 having a negative electrode active material made of an aluminum alloy containing porous lithium; a charging/discharging device 30 connected to the lithium ion capacitor 20; and a charging/discharging control device 40 for controlling charge/discharge power of the charging/discharging device 30. An electric vehicle comprises an inverter 50 connected to the electrical power system 45 and a three-phase synchronous motor 60 driven by the inverter 50 as an electric motor.

Description

  The present invention relates to a power supply system and a vehicle using the same.

  In recent years, research and development of automobiles taking into account the prevention of global warming has been actively conducted. One promising example is an electric vehicle, and among them, an electric vehicle using a capacitor with a high output density in a power supply system has attracted attention.

  For example, as an electric vehicle using an electric double layer capacitor in the power supply system, a protective case for the electric double layer capacitor that also serves as a reinforcement of the vehicle body structure is integrated with the vehicle body or the vehicle body frame at the bottom of the vehicle body or a part of the frame. Is known (see Patent Document 1).

  Also in the field of construction machinery, in recent years, electric construction machines have been developed.

  For example, in a vehicle called a wheel loader 10, a capacitor module 22 composed of a plurality of electric double layer capacitors (power supply devices) is covered with a casing 23, and the casing 23 is exposed to the outside so that it also serves as an exterior cover. . Then, at least the top plate 30 constituting the housing 23 has a multiple structure having a plurality of upper and lower planar portions 31 and 32, and a ventilation portion 33 through which outside air flows is formed between these planar portions 31 and 32. The thing of the structure which was made is known (refer patent document 2).

JP 2000-351329 A JP 2008-14087 A

  However, in the electric vehicle disclosed in Patent Document 1, since an electric double layer capacitor is used in the power supply system, the output density is large but the energy density is insufficient. Therefore, if sufficient energy is to be secured, there is a problem that the weight is inevitably increased and the volume is increased.

  In the wheel loader 10 disclosed in Patent Document 2, since an electric double layer capacitor is used, in addition to insufficient energy density, heat generation due to internal resistance tends to increase. When such a large amount of heat is generated, performance deterioration of the electric double layer capacitor due to temperature rise occurs. Therefore, in order to prevent this performance deterioration, the electric double layer capacitor in the power supply system has a problem that a heat dissipating facility must be provided.

  An object of the present invention is to provide a power supply system that satisfies both a predetermined output density and an energy density, is lightweight, small, and does not require a heat dissipation facility for a capacitor, and a vehicle using the same.

  In order to achieve this object, an invention according to claim 1 of the present invention is a power supply system, and controls a capacitor, a charge / discharge device connected to the capacitor, and a charge / discharge power of the charge / discharge device. The capacitor is a lithium ion capacitor having a negative electrode active material made of a porous lithium-containing aluminum alloy.

  The invention according to claim 2 is a vehicle including the power supply system according to claim 1, an inverter connected to the power supply system, and an electric motor driven by the inverter.

As described above, the invention according to claim 1 of the present invention is a power supply system for controlling a capacitor, a charge / discharge device connected to the capacitor, and charge / discharge power of the charge / discharge device. Charge and discharge control device, the capacitor is a lithium ion capacitor having a porous lithium-containing aluminum alloy negative electrode active material, satisfying both a predetermined output density and energy density, lightweight, compact, and Therefore, it is possible to provide a power supply system that does not require capacitor heat dissipating equipment. In addition, it is possible to supply a predetermined voltage and a predetermined current required for the vehicle, the electric device, and the like. Furthermore, since the capacitor is prevented from being overcharged and overdischarged, there is an effect that the cycle life of the capacitor is further improved. Therefore, the lifetime of the power supply system is extended.
The invention according to claim 2 of the present invention is a vehicle including the power supply system according to claim 1, an inverter connected to the power supply system, and an electric motor driven by the inverter. The structure as a vehicle is also simple, lightweight and compact. Further, by adopting the power supply system in a vehicle, it is possible to improve the travel distance.

It is a schematic diagram for demonstrating the synthesis | combining method of one Embodiment of the negative electrode active material which concerns on this invention. It is a partially expanded schematic diagram of the negative electrode active material formed by the synthesis method shown in FIG. 3 is a drawing-substituting photograph showing a surface state of the surface of the surface layer portion of the negative electrode active material shown in FIG. 2 observed with a scanning electron microscope from the direction of arrow A. FIG. 3 is a drawing-substituting photograph showing a cross-sectional state of the negative electrode active material shown in FIG. 2 as observed by a scanning electron microscope. It is explanatory drawing for demonstrating the definition of the surface porosity of the surface layer part of the negative electrode active material shown in FIG. It is a schematic block diagram for demonstrating one Embodiment of the lithium ion capacitor which concerns on this invention. 1 is a schematic block diagram for explaining an embodiment of a power supply system according to the present invention and a vehicle using the same.

  Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

(Embodiment 1)
FIG. 1 is a schematic view for explaining a synthesis method of one embodiment of a negative electrode active material according to the present invention.

  In FIG. 1, 1 is a container, 2 is an aluminum foil connected to the negative electrode side, 3 is a lithium plate connected to the positive electrode side, and 4 is an electrolytic solution poured into the container 1.

The aluminum foil 2 is prepared in advance under the following pretreatment conditions.
(Pretreatment of aluminum foil 2)
An aluminum foil having a purity of 99.9% and a thickness of 110 μm is etched for 500 seconds in an aqueous solution containing 10% by mass hydrochloric acid and 0.1% by mass sulfuric acid in an electrolyte at 38 ° C. at 60 Hz and a current density of 180 mA / cm ^2. And washed with ion-exchanged water.

In FIG. 1, a lithium plate 3 connected to the positive electrode side and the negative electrode side, and the aluminum foil 2 pretreated in advance are used as an electrolyte {concentration 1 mol; electrolyte (LiPF ₆ ), organic solvent (ethylene carbonate (EC): (Diethyl carbonate (DEC) = 1: 1 mixed solution)} 4 so as to be opposed to each other, alloyed by controlling the potential of the aluminum foil 2 to 25 mV (vs. Li / Li ⁺ ) and electrolyzing at 50 ° C., Test No. shown in Table 1 below. 1 porous negative electrode active material 12 made of lithium-containing aluminum alloy {hereinafter referred to as negative electrode active material 12 (see FIGS. 2 to 6)} was synthesized.

  FIG. 2 is a partially enlarged schematic view of the negative electrode active material 12 formed by the synthesis method shown in FIG. In FIG. 2, the negative electrode active material 12 is composed of a surface layer portion 12a and a base portion 12b. The surface layer portion 12a has a three-dimensional network skeleton and a structure having a large number of pores (presents a so-called sponge structure). The opening diameter D of these pores is 0.5 μm to 2 μm. Moreover, the pore mentioned here is a general term including the case where some holes generated due to the pretreatment conditions of the aluminum foil 2 are included.

  FIG. 3 is a drawing-substituting photograph showing the surface state of the surface of the surface layer portion 12a of the negative electrode active material 12 shown in FIG. 2 observed with a scanning electron microscope from the direction of arrow A.

  4 is a drawing-substituting photograph showing a cross-sectional state of the negative electrode active material 12 shown in FIG. 2 as observed by a scanning electron microscope. From FIG. 4, the average thickness of the surface layer portion 12a is about 5 μm. The predetermined thickness of the surface layer portion 12a is preferably 1 μm to 50 μm in view of the object of the present invention. 2 to 4, it was explained that the surface layer portion 12a on the surface (one surface side) of the negative electrode active material 12 has the sponge-like structure, but on the back surface (other surface side) of the negative electrode active material 12. There is also a surface layer portion 12a, and the structure of the surface layer portion 12a is also the sponge-like structure.

  As described above, the surface layer portion 12a has a large number of pores, and the opening diameter D of these pores is preferably 0.1 to 5 μm. This is because if the thickness exceeds 5 μm, the surface area of the negative electrode active material 12 decreases and the capacity decreases, and if it is less than 0.1 μm, it is difficult for the electrolyte solution described later to enter the pores. However, the cross-sectional shape of the pores is not limited to a circle.

  Further, the surface and cross-sectional properties of the surface layer portion 12a having a large number of pores were observed with the scanning electron microscope described above, and the surface aperture ratio was measured. This surface aperture ratio follows the definition shown in FIG. In this definition, the opening diameter D of the pores is an average diameter, and the distance L between the pores is also an average length. The surface area ratio of the surface layer portion 12a is preferably 10 to 80%. This is because if it is less than 10%, the stress due to volume expansion due to an increase in the lithium content in the negative electrode active material 12 during charging is insufficient, and if it exceeds 80%, the machine as the negative electrode active material 12 is insufficient. This is thought to be because the mechanical strength is insufficient.

In the present embodiment, the case where the thickness is 110 μm has been described as an example of the aluminum foil 2. However, the thickness is not necessarily limited to this, and a thickness of about 5 μm to 200 μm can be used. In the present embodiment, an example of substantially consisting of Al and Li as an aluminum alloy has been described. However, the present invention is not necessarily limited to this, and aluminum containing elements such as Mg and Zn in addition to Li It can also be an alloy. In addition, the aluminum alloy of this invention may contain 0.05 atom (at)% or less of Si, Fe, Cu, Mn, Mg, Zn, Ti etc. as an unavoidable impurity. In the present embodiment, as a condition for synthesizing the negative electrode active material 12, an aluminum foil 2 having a purity of 99.9% is connected to the negative electrode side, and the potential is controlled to 25 mV (vs. Li / Li ⁺ ), Although an example of alloying by electrolysis in an electrolytic solution at 50 ° C. has been described, it is not necessarily limited thereto. It can be alloyed with Li by electrolysis.

(Embodiment 2)
FIG. 6 is a schematic configuration diagram for explaining an embodiment of a lithium ion capacitor according to the present invention.

  In FIG. 6, 10 is a container, 12 is a negative electrode active material obtained by the synthesis described in Embodiment 1, 13 is an aluminum current collector, 14 is a positive electrode active material, and 15 is impregnated with an electrolyte. A separator 20 is a lithium ion capacitor. In the present embodiment, the same elements as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

The separator 15 is sandwiched between the negative electrode active material 12 and the positive electrode active material 14 having activated carbon (BET specific surface area: 800 to 1300 m ² / g) provided by applying and drying on the current collector 13. The electrolyte solution impregnated in the separator 15 is an electrolyte solution having a concentration of 1.5 mol composed of an electrolyte (LiBF ₄ ) and an organic solvent {a mixed solution of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 1}. It is. The lithium ion capacitor 20 configured as described above was tested in the test No. 1 shown in Table 1 of the first embodiment described above. As shown in Table 2 below, the test No. It was set to 1.

  Test No. shown in Table 2 above. 1 is a structure in which the lithium content in the negative electrode active material 12 increases and the volume expands during charging, but the surface layer portion 12a of the negative electrode active material 12 has a three-dimensional network skeleton and has a large number of pores. (So-called sponge-like structure), the stress due to volume expansion due to an increase in the lithium content in the negative electrode active material 12 during charging can be reduced (the influence is absorbed). Therefore, even if the lithium ion capacitor 20 is used without charge / discharge control, the cycle life is 800, which satisfies a predetermined cycle life (600 or more). Further, the present lithium ion capacitor 20 is a power storage mechanism based on a chemical reaction, and the energy density is 70 (Wh / kg) as shown in Table 2 above, which is per weight and per volume compared to the electric double layer capacitor. Both are about 10 times or more. This energy density {70 (Wh / kg)} satisfies the energy density {60 (Wh / kg) or more} required as a power source for a vehicle such as an electric vehicle, and a necessary sustaining power (predetermined value) The ability to realize the travel distance of Further, the present lithium ion capacitor 20 has an output density of 3100 (W / kg) as shown in Table 2 above, and an output density {3000 (W / kg) or more} required as a power source for a vehicle such as an electric vehicle. And has the necessary instantaneous power as the power source. Further, the present lithium ion capacitor 20 does not generate dendrites.

  In the present embodiment, test No. 1, the example in which the content of Li in the negative electrode active material 12 is 30 at% has been described. However, the present invention is not necessarily limited thereto. The content of Li in the negative electrode active material 12 is preferably 5 at% to 50 at%. The reason is that if it is less than 5 at%, the energy density required as a power source for a vehicle such as an electric vehicle cannot be satisfied, and if it exceeds 50 at%, dendrites are likely to be generated. As content of Li in the negative electrode active material 12, it is more preferable to set it as 5 at%-50 at% from the point of generation | occurrence | production of the sustainability mentioned above and dendrite.

  In the present embodiment, a configuration in which a current collector is not separately provided for the negative electrode active material 12 has been described. However, the present invention is not necessarily limited thereto. For example, a current collector may be separately provided for the negative electrode active material 12 such that the negative electrode active material 12 is lightly pressed against a copper current collector via a conductive paste to form a negative electrode.

(Embodiment 3)
FIG. 7 is a schematic block diagram for explaining an embodiment of a power supply system according to the present invention and a vehicle using the same. In the present embodiment, the same elements as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 7, reference numeral 45 denotes a power source having a lithium ion capacitor 20, a charge / discharge device 30 connected to the lithium ion capacitor 20, and a charge / discharge control device 40 for controlling the charge / discharge power of the charge / discharge device 30. System. Reference numeral 80 denotes an electric vehicle as a vehicle. The electric vehicle 80 includes a power supply system 45, an inverter 50 connected to the power supply system 45, and driving wheels 70 and 71 using AC power supplied from the inverter 50. And a three-phase synchronous motor 60 as an electric motor to be driven. The electric vehicle 80 employs a front wheel drive system, and driven wheels 72 and 73 are disposed at the rear of the electric vehicle 80.

  The charging / discharging device 30 is generally composed of a DC-DC converter or the like. The power supply system 45 detects the output voltage of the charging / discharging device 30 and outputs a signal corresponding to the output voltage from a voltage detector (not shown) and a voltage for detecting the voltage of the lithium ion capacitor 20. Based on the output signal of the detector (not shown) and the output signal of the current detector (not shown) that detects the current of the lithium ion capacitor 20, the charge / discharge control device 40 determines the charge / discharge power of the charge / discharge device 30. It is configured to control with. Therefore, it is possible to realize a power supply system that satisfies both a predetermined output density and an energy density, is lightweight, small, and does not require a capacitor heat dissipating facility. Further, by using such a power supply system 45, a predetermined voltage and a predetermined current necessary for the electric vehicle 80 can be supplied. That is, it becomes possible to supply AC power having a predetermined variable voltage and variable frequency to the three-phase synchronous motor 60 via the inverter 50.

  In addition, since the charging / discharging control device 40 is employed in the power supply system 45, the overcharge and overdischarge of the lithium ion capacitor 20 are prevented, so that the cycle life of the lithium ion capacitor 20 is further improved to 1200. (See test No. 2 in Table 2 above). Therefore, the life of the power supply system 45 is also extended.

  In addition, since the power supply system 45 is used in the electric vehicle 80, the structure of the vehicle is simple, lightweight, and compact. Further, by adopting the power supply system 45 in the electric vehicle 80, it is possible to improve the travel distance.

  In the present embodiment, an electric vehicle has been described as an example of a vehicle, but the present invention is not necessarily limited thereto. For example, a construction machine such as a wheel loader having the power supply system 45 as a vehicle is also included in the technical scope of the present invention. In such a construction machine, it is possible not only to make the power supply system 45 contribute to the improvement of the travel distance, but also to contribute to the driving of the bucket used for loading earth and sand in a dump truck or removing snow. It is also possible.

  In the vehicle of the present invention, it is more preferable that the regenerative energy at the time of regenerative braking is stored in the lithium ion capacitor 20. Further, the vehicle is not limited to driving using only the power supply system 45, and may be a hybrid system using an engine system together.

DESCRIPTION OF SYMBOLS 1, 10 Container 2 Aluminum foil 3 Lithium plate 4 Electrolytic solution 12 Negative electrode active material 12a Surface layer part 12b Base part 13 Current collector 14 Positive electrode active material 15 Separator 20 impregnated with electrolytic solution Lithium ion capacitor 30 Charging / discharging device 40 Charging / discharging Control device 45 Power supply system 50 Inverter 60 Three-phase synchronous motors 70 and 71 Drive wheels 72 and 73 Driven wheels 80 Electric vehicle

Claims (2)

  A power supply system comprising a capacitor, a charge / discharge device connected to the capacitor, and a charge / discharge control device for controlling charge / discharge power of the charge / discharge device, the capacitor containing porous lithium A power supply system comprising a lithium ion capacitor having an aluminum alloy negative electrode active material. A vehicle comprising the power supply system according to claim 1, an inverter connected to the power supply system, and an electric motor driven by the inverter.

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