JP7157619B2 - Secondary batteries, battery packs and power systems - Google Patents

Description

The present invention relates to secondary batteries, battery packs and power systems.

Conventionally, studies have been made to improve responsiveness in a high frequency band by reducing the parasitic inductance in the battery.

For example, in Patent Document 1, a positive current collecting electrode and a negative current collecting electrode provided in parallel form two current paths through which currents of the same magnitude flow in opposite directions. A battery is disclosed in which the electromagnetic induction caused by the current flowing in each direction is canceled by the magnetic field and the parasitic inductance can be reduced.

Japanese Patent Application Laid-Open No. 2007-220372

The battery described in Patent Document 1 improves the arrangement of the collector electrodes, but focuses on parasitic inductance due to magnetic field cancellation, and there is room for improvement regarding the impedance inside the positive and negative electrodes. it is conceivable that.

In the high frequency band, it is considered that the capacitance component of the electrode material applied to the electrode current collector also contributes greatly to the above impedance.

An object of the present invention is to adjust the distribution of impedance, including capacitance, in the electrodes of a secondary battery and reduce the impedance of the secondary battery in a high frequency band.

The secondary battery of the present invention has a positive electrode and a negative electrode in which an electrode material is applied to current collectors, and a separator provided between the positive electrode and the negative electrode. , tabs are attached, and at least one of the positive electrode and the negative electrode makes the impedance in the vicinity of the tab smaller than the impedance in other regions.

According to the present invention, it is possible to adjust the impedance distribution including the capacitance in the electrodes of the secondary battery and reduce the impedance of the secondary battery in the high frequency band.

1 is a schematic configuration diagram showing the internal configuration of a lithium ion battery; FIG. FIG. 4 is a cross-sectional view showing an example of an electrode; 3 is a configuration diagram showing a main part of an equivalent circuit model of a battery; FIG. FIG. 2 is a configuration diagram showing essential parts of an equivalent circuit model of a battery according to the first embodiment; FIG. FIG. 3 is a configuration diagram showing an equivalent circuit model related to a high frequency band; 6 is a graph showing the results of simulation using the equivalent circuit model of FIG. 5; FIG. 5 is a cross-sectional view showing an example of an electrode according to the second embodiment; FIG. 5 is a schematic configuration diagram showing an electrode according to a third embodiment; FIG. 11 is a schematic configuration diagram showing a metal foil that constitutes an electrode according to a fourth embodiment; FIG. 10 is a schematic configuration diagram showing a battery according to a fifth embodiment; FIG. 11 is a schematic configuration diagram showing a battery pack according to a sixth embodiment; FIG. 11 is a schematic configuration diagram showing a power system according to a seventh embodiment; FIG. 12 is a schematic diagram showing a manufacturing process of an electrode according to the eighth embodiment;

Embodiments of the present invention will be described below.

The following descriptions show specific examples of the content of the present invention, and the present invention is not limited to these descriptions. changes and modifications are possible. In addition, in all the drawings for explaining the present invention, parts having the same functions are denoted by the same reference numerals, and repeated explanations thereof may be omitted.

First, a configuration example of a battery, which is a prerequisite for embodiments of the present invention, will be described.

FIG. 1 shows the minimum unit of the internal configuration of a lithium ion battery.

As shown in the figure, the battery comprises a negative electrode 10, a positive electrode 11 and a separator 12. FIG. The negative electrode 10 and the positive electrode 11 respectively have a negative electrode tab 13 and a positive electrode tab 14 as current paths with the outside. The negative electrode 10, the positive electrode 11, and the separator 12 are filled with an electrolytic solution in which a lithium salt is dissolved, and the electrolytic solution conducts ions.

For example, in a laminate type battery, a large number of minimum unit batteries shown in FIG. 1 are stacked and connected in parallel. In this case, the negative electrode tab 13 and the positive electrode tab 14 are put together and integrated by welding or the like to form a battery within one laminate.

Examples of the configuration of the positive electrode 11 and the negative electrode 10 are as follows.

The positive electrode 11 is formed by binding a positive electrode active material represented by an NMC active material _{( ternary} system _{LiNixMnyCozO2 )} and a conductive aid with a binder, and coating the aluminum foil (positive electrode current collector) with the material. do. On the other hand, the negative electrode 10 is formed by binding a negative electrode active material, typically graphite, and a conductive aid with a binder, and applying the resultant to a copper foil (negative electrode current collector).

FIG. 2 schematically shows a cross section of an electrode.

In the electrode shown in this figure, an electrode material 101 is applied to both surfaces of a metal foil 100 (current collector). Although it may be applied on one side, it is common to apply it on both sides in order to improve the energy density.

Next, an equivalent circuit model of a battery will be described.

In order to discuss the characteristics in the high frequency band, FIG. 3 shows only the equivalent circuit model relevant in the high frequency band.

In this figure, an equivalent circuit 200 is derived from the electrode material of the battery in the vicinity of the tab. The equivalent circuit 210, on the other hand, is derived from the electrode material in the portion far from the tab.

The equivalent circuit 200 includes an electromotive force 201 of the battery, a parallel circuit of the capacitance 202 due to the reaction of electric double layer formation and the charge transfer resistance 203 of the electrode active material, a parallel circuit of the inductance 204 in the electrode and the inductance part resistance 205, and It is composed of a direct current resistance 206 which is the sum of the electrolyte resistance of the battery and the resistance of the members.

In the entire electrode, an equivalent circuit 200 derived from the electrode material is connected to an external circuit via an inductance 207 and a resistor 208 derived from the tab. The farther from the tab, the more susceptible it is to the inductance 209 of the copper foil. Therefore, the equivalent circuit 210 is added with the inductance 209 integrated by the electrode length, and is connected to the inductance 207 and the resistor 208 .

In a normal electrode, the electrode material 101 is uniformly applied to the entire surface of the electrode foil, so the equivalent circuit 200 derived from the electrode material near the tab and the equivalent circuit 210 derived from the electrode material far from the tab are the same. becomes.

The absolute value Z of the impedance of the inductance is represented by the following formula (1). In the formula, ω represents the frequency and L represents the inductance value.

From the above formula (1), it is found that in a high frequency band, the inductance 209 is greatly affected and the impedance becomes high, so it is difficult to supply electric power from the electrode material far from the tab. In other words, in a high frequency band, it means that the current concentrates in the vicinity of the tab. Therefore, in order to supply electric power in a high frequency band, it is considered effective to reduce the inductance 207 and the resistance 208 of the tab and to provide the capacitance near the tab with the capacity corresponding to the capacitance.

Embodiments will be described below.

(First embodiment)
The first embodiment improves the characteristics in the high frequency band by making the equivalent circuits 200 and 210 of FIG.

FIG. 4 shows the configuration.

As shown in this figure, the battery for high frequencies has a thick negative electrode tab 300, a thick positive electrode tab 301, an electrode material application portion 302 with a higher proportion of activated carbon or the like to increase the capacitance component, and an electrode material of a battery with a normal composition. It is configured by an application unit 303 .

Both the negative electrode tab 300 and the positive electrode tab 301 are thickened to provide close proximity between the electrodes. This is to reduce the tab-derived inductance 207 and resistance 208 shown in FIG.

The resistance is thickness dependent according to equation (2) below. In the formula, R is the resistance value, ρ is the resistivity, l is the current path length, and A is the cross-sectional area.

On the other hand, the inductance of the copper foil of the main current path of the battery depends on the current path length according to the following equation (3). In the formula, L is the inductance (unit: nH), l is the current path length, w is the width of the conductor, and t is the thickness of the copper foil.

Adding a capacitive component to such a region near the electrode tab where the impedance in the high frequency band is lowered enables power supply at high frequency. To this end, an electrode material is applied that contains more components than the electrode material of normal composition, such as a material that increases the capacitance 202 (FIG. 3), such as activated carbon with a large surface area that increases the area for ion adsorption and desorption. An electrode material having a normal composition is applied to a region other than the vicinity of the tab where the impedance is high in a high frequency band. With such a configuration, the capacitance 202 (FIG. 3) derived from the electric double layer increases in the vicinity of the tab. Here, the activated carbon or the like preferably has a specific surface area of about 500 to 3000 m ² /g.

This effect will be explained using an equivalent circuit that is simply expressed by limiting the configuration of FIG. 4 to high-frequency response components.

FIG. 5 shows an equivalent circuit model related to the high frequency band.

In FIG. 5, the capacitance corresponding to the electrode material applied portion 302 (FIG. 4) with an increased capacitance component near the tab is the capacitance 400, and the capacitance of the electric double layer in the electrode material applied portion 303 (FIG. 4) of the normal composition is A capacitance 401 is a capacitance corresponding to minutes.

FIG. 6 shows the results of a simulation performed by changing the capacitances of the capacitances 400 and 401 as parameters in the configuration of FIG. The horizontal axis indicates frequency, and the vertical axis indicates impedance. Both the horizontal and vertical axes are logarithmic.

The dotted line indicates the case where a conventional electrode material with a normal composition is applied to the entire surface (Comparative Example 1), and the dashed line indicates the case where an electrode material containing a large amount of a component that increases capacitance is applied to the entire surface (Comparative Example 2). , the solid line indicates the case where an electrode material containing a large amount of a component that increases the capacitance only in the vicinity of the tab, which is the present embodiment, is applied, that is, the case where the capacitance 400 is increased, and the broken line indicates the case where the capacitance increases only in the portion far from the tab. It shows the case where an electrode material containing many increasing components is applied, that is, the case where the capacitance 401 is increased (Comparative Example 3).

In this simulation, the "near the tab" means that the vertical width of the electrode material application portion 302 in FIG. 4 is half the vertical width of the electrode, in other words, It means that the width of the portion 302 in the vertical direction in the drawing is the same as the width of the electrode material application portion 303 in the vertical direction in the drawing. This means that inductance 207 and inductance 209 are equal and resistance 206 and resistance 208 are equal. This is Example 1. On the other hand, in Comparative Example 3, contrary to Example 1, an electrode material application portion 303 was provided in the vicinity of the tab, and an electrode material application portion 302 was provided in a portion far from the tab. The width in the vertical direction is the same as the width of the electrode material application portion 302 in the vertical direction in the figure.

Also, the capacitance ratio between the capacitance 400 and the capacitance 401 in FIG. 5, in other words, the capacitance ratio between the electrode material application portion 302 and the electrode material application portion 303 was set to 10:1.

In FIG. 6, it is desirable to configure the electrodes so that the impedance is low in the frequency range of several kHz to 50 kHz. More preferably, the impedance is low in the frequency range from several kHz to 20 kHz.

As shown in (a) of the figure, in the frequency region of 20 kHz or less, the present embodiment and Comparative Examples 2 and 3 have lower impedance than Comparative Example 1. FIG. This is due to the application of a component that increases the capacitance over the application of the normal electrode material alone.

In the case of Comparative Example 1, the impedance is minimal at approximately 40 kHz.

In the case of this embodiment, the impedance is minimal at approximately 20 kHz. In the case of Comparative Examples 2 and 3, the impedance is minimal at approximately 12-13 kHz. That is, in the case of the present embodiment, compared with Comparative Examples 2 and 3, the resonance point at which the impedance is minimized is shifted to the high frequency side.

Comparing this example with Comparative Examples 2 and 3, as shown in (b) of the figure, the minimum value of impedance in this example is the smallest. In addition, in the frequency range of 10 to 50 kHz, the integral value of the impedance of this embodiment is the smallest.

As described above, in the case of this embodiment, it is considered that the impedance in the high frequency region is reduced, and power response is possible even at high frequencies.

In this way, by dividing roles such that the area near the tab can handle high frequencies and the area away from the tab serves as an area for taking out the electrochemical reaction of a normal battery, the electrode is superior in both the high frequency range and the low frequency range. design becomes possible.

In the simulation shown in this drawing, the width of the electrode material application portion 302 (FIG. 4) in the vicinity of the tab was set to 1/3 of the width of the electrode, but the present invention is not limited to this. , the width of the electrode material application portion 302 (FIG. 4) in the vicinity of the tab may be less than half the width of the electrode.

A configuration such as that of Example 1 is effective for at least one of the positive electrode and the negative electrode.

In the present specification, the term “near the tab” refers to a region up to half the distance from the side of the electrode to which the tab is attached to the opposite side when the shape of the electrode is rectangular. When the shape of the electrode is another shape, such as a circle or an ellipse, it refers to the area on the tab side partitioned by a straight line perpendicular to the straight line connecting the midpoint of the attached portion of the tab and the center of gravity of the circle or ellipse. do. In summary, generally speaking, the term “near the tab” refers to the area on the tab side partitioned by a straight line perpendicular to the straight line connecting the center of gravity of the electrode shape and the midpoint of the attached portion (line segment) of the tab. do.

In summary, the impedance in the vicinity of the tab, even if the width of the portion coated with the electrode material containing a large amount of the component that increases the capacitance is reduced to 1/3 as in Example 1, is defined as "the The impedance in the "neighborhood" is smaller than the impedance in other regions.

(Second embodiment)
A means for reducing the impedance near the tab will be described. Lower impedance is made possible by using a thin separator 500 .

FIG. 7 shows a cross section of the battery of FIG.

In FIG. 7, a negative electrode foil 501 is coated with a negative electrode material 502 . A positive electrode material 504 is applied to the positive electrode foil 503 . A thin separator 500 separates the negative electrode material 502 and the positive electrode material 504 .

DC resistance 206 in FIG. 3 is the sum of the resistance of the electrolyte and the resistance of the foil or the like. The resistance of the electrolytic solution can be expressed by an equation obtained by replacing the resistivity of the above equation (1) with ionic conductivity.

Therefore, the resistance of the electrolyte is proportional to the ion conduction length. Therefore, by thinning the separator 500 in FIG. 7, the DC resistance 206 can be lowered. This makes it possible to reduce the impedance of the battery and respond even at high frequencies. Here, the thickness of the separator 500 is desirably 1 μm or more and 100 μm or less. If the thickness is less than 1 μm, the strength of the film will be insufficient.

(Third embodiment)
The current path can be controlled by slitting the electrodes.

FIG. 8 schematically shows the electrodes of the third embodiment.

In this figure, an electrode 600 is coated with an electrode material and has a tab 601 as in the first or second embodiment. In the electrode 600, a slit 602 is provided in the central portion of the side opposite to the side on which the tab 601 is provided.

The presence of the slit 602 ensures that the current path of the electrode 600 passes through the vicinity of the tab 601 . Therefore, current concentrates in the vicinity of the tab 601, especially in a high frequency band.

As a result, the impedance near the tab 601 is relatively low compared to the portion far from the tab 601 . For this reason, the utilization factor on the high frequency side near the tab 601 is improved. By providing the slit 602 in the electrode 600 to limit the current path in this way, it is possible to designate a location where current concentration with a small impedance occurs in the plane of the electrode 600 . By adding a capacitance component here, it is possible to improve the high-frequency characteristics. The slits 602 in this embodiment may be provided only in the metal foil and the electrode material may be uniformly applied as usual. Also, depending on the shape of the electrode and the position of the tab, it is important to design according to the shape of the electrode and the position of the tab, because the position of the slit to concentrate the current in the low inductance portion differs.

(Fourth embodiment)
In the third embodiment, the electrodes with slits were used in order to increase the usage rate of the vicinity of the tab, but similar effects can be expected by providing through holes in the metal foil.

FIG. 9 schematically shows the metal foil of the electrode of the fourth embodiment.

In this figure, the metal foil 700 has a through hole 701 in a portion far from the tab. As a result, when the electrode material is applied, the electrode material is filled in the portion where the metal exists in a normal electrode, so a high energy density can be realized.

On the other hand, the portion where the through-hole 701 exists has a reduced current path, resulting in an increase in resistance. Therefore, by not forming the through hole 701 in the vicinity of the tab and by forming the through hole 701 in the portion far from the tab, the resistance in the vicinity of the tab becomes relatively small and the current concentrates. As a result, the utilization rate near the tab is improved in the high frequency band.

(Fifth embodiment)
As a means for reducing the inductance near the tabs of the battery, there is a means for canceling the magnetic field by opposing the positive electrode tab and the negative electrode tab.

FIG. 10 is a schematic configuration diagram showing the battery of the fifth embodiment.

The battery shown in the figure has electrodes housed in a laminate-type battery container 800 . The negative electrode tab 801 and positive electrode tab 802 are connected to an external circuit. An insulating plate 803 is interposed between the negative electrode tab 801 and the positive electrode tab 802 for insulation.

The inductance of the wiring is reduced by the canceling effect of the magnetic field when the wiring is arranged so that the current flows in the opposite direction between the facing wirings. In order to reduce the inductance, it is necessary to shorten the distance between these wirings to enhance the effect of canceling the magnetic field.

In the configuration of this figure, it is necessary to shorten the distance between the negative electrode tab 801 and the positive electrode tab 802, but if the negative electrode tab 801 and the positive electrode tab 802 are brought into contact with each other, a short circuit will occur and the battery will be damaged. , must be insulated. Therefore, an insulating plate 803 is required.

With the configuration shown in this figure, when a current 804 flows through the negative electrode tab 801 , a reverse current 805 flows through the positive electrode tab 802 . As a result, the direction of the magnetic field between the tabs is reversed, so that the inductance 207 in FIG. 3 is reduced and the responsiveness at high frequencies can be improved.

(Sixth embodiment)
A means for reducing inductance in the battery pack will be described.

In general, batteries have a low voltage of about 3.7 V, so they are often serially connected and used as a battery pack. In order to reduce the inductance within the battery pack, it is effective to reduce the inductance between the batteries in addition to reducing the inductance within the battery.

FIG. 11 schematically shows a battery pack composed of two batteries connected in series.

In this figure, the battery pack includes batteries 900 and 903 . Battery 900 has a negative electrode tab 902 and a positive electrode tab 901 . Battery 903 has a positive tab 904 and a negative tab 905 .

When the battery 900 and the battery 903 are serialized, the negative electrode tab 902 and the positive electrode tab 904 are connected. For example, when they are serialized by screws or the like, the negative electrode tab 902 and the positive electrode tab 904 are fastened. In this serialization, the battery 900 and the battery 903 are placed back to back. By placing them back to back, when the current flows in the direction of the current 906 in the battery 900 , the current flows in the direction of the current 907 in the battery 903 . As a result, the directions of the magnetic fields between the batteries are reversed, so that the inductance 207 in FIG. 3 is reduced, and the response at high frequencies can be improved.

When three or more secondary batteries are connected in series, the tabs of two adjacent secondary batteries are connected. In that case, it is preferable that the positive electrode tab and the negative electrode tab of the secondary battery are arranged with a space therebetween as shown in FIG.

(Seventh embodiment)
In this embodiment, the overall configuration of a power system in which the batteries described in the first to sixth embodiments are connected to a load will be described.

FIG. 12 shows a power system with batteries connected to the load.

In this figure, a motor 1000 is assumed as the load. A motor 1000 is connected via an inverter 1001 to a high-frequency compatible battery 1002 as a power supply source. The inverter 1001 and the high frequency compatible battery 1002 are connected via a wiring 1003 . Separately, if energy as a battery is required, a capacitive battery 1004 (another power supply device) is connected. Inverter 1001 and capacitive battery 1004 are connected via wiring 1005 . If the high-frequency battery 1002 is sufficient to supply energy to the motor 1000, the capacitive battery 1004 is unnecessary. It is desirable that the wiring 1003 be as short as possible in order to reduce its own impedance. A length of 1 m or less is desirable. More preferably, the length is 50 cm or less.

With such a configuration, the high-frequency compatible battery 1002 plays the role of a capacitor that smoothes the ripple current and voltage from the inverter 1001, and power is supplied from the capacitive battery 1004 when a large amount of power is required. becomes possible. The advantage of changing from the smoothing capacitor to the high-frequency compatible battery 1002 is that by using the reaction derived from the electrode active material of the battery, the component that can respond to the load on the lower frequency side than the smoothing capacitor is increased. is. Since the high-frequency compatible battery 1002 bears such a load on the low-frequency side, the load on the capacitive battery 1004 is reduced, which contributes to suppression of heat generation and extension of life.

As described in equation (3) above, the longer the current path length, the greater the inductance.

Therefore, the high-frequency compatible battery 1002 is installed at a position close to the inverter 1001, and the wiring 1003 is also arranged so that the wiring on the + side (positive electrode side) and the wiring on the - side (negative electrode side) face each other, thereby It is possible to reduce the inductance of the wiring 1003 due to the canceling effect of . On the other hand, since the capacitive battery 1004 does not consider high frequency, the wiring 1005 may be long and does not need to face each other.

Therefore, the high-frequency compatible battery 1002 is connected to the inverter 1001 at a position closer than the capacitive battery 1004, and the connection uses the wiring 1003 facing each other to reduce the inductance, thereby reducing the high-frequency ripple current. Moreover, it is possible to reduce the load on the capacitive battery.

(Eighth embodiment)
When manufacturing the electrode of the battery (FIG. 4) of the first embodiment, the coating process consists of two steps.

FIG. 13 is a schematic diagram showing the manufacturing process of the electrode.

As shown in this figure, a metal foil 1100 is connected to a coating machine. The metal foil 1100 is attached to a predetermined position in a roll state and sent out. An electrode material 1101 with an increased capacitance component (a material applied to the electrode material application portion 302 in FIG. 4), such as a material containing a large amount of activated carbon, is applied to the metal foil 1100 by the application head 1102 . Further, the electrode material 1103 of the normal composition battery (the material applied to the electrode material application portion 303 of the normal composition battery in FIG. 4) is applied to the metal foil 1100 by the application head 1104 .

In this figure, application is performed in a state where the application head 1102 is slightly ahead of the application head 1104 . However, the present invention is not limited to such a coating method, and the coating by the coating head 1102 and the coating head 1104 may be performed simultaneously in parallel.

The application can be performed by a spray method, roll coating, or the like, and the type is not limited. Also, the application order of the electrode material 1101 and the electrode material 1103 may be reversed.

The applied metal foil 1100 is wound up on a roll after drying.

Since the process of applying the positive electrode and the negative electrode is substantially the same, the process of this embodiment is applied to both the positive electrode and the negative electrode.

10: negative electrode, 11: positive electrode, 12: separator, 13: negative electrode tab, 14: positive electrode tab, 100: metal foil, 101: electrode material, 200: equivalent circuit, 201: electromotive force of battery, 202: capacitance, 203: Charge transfer resistance, 204: Inductance, 205: Inductance part resistance, 206: DC resistance, 207: Inductance, 208: Resistance, 209: Inductance, 210: Equivalent circuit, 300: Negative electrode tab, 301: Positive electrode tab, 302, 303: Electrode material application part, 400, 401: capacitance, 500: separator, 501: negative electrode foil, 502: negative electrode material, 503: positive electrode foil, 504: positive electrode material, 600: electrode, 601: tab, 602: slit, 700: metal Foil, 701: Through hole, 800: Laminated battery container, 801: Negative electrode tab, 802: Positive electrode tab, 803: Insulating plate, 804, 805: Current, 900, 903: Battery, 901, 904: Positive electrode tab, 902 , 905: negative electrode tab, 906, 907: current, 1000: motor, 1001: inverter, 1002: high frequency compatible battery, 1003: wiring, 1004: capacitive battery, 1005: wiring, 1100: metal foil, 1101, 1103: electrode Material, 1102, 1104: Application head.

Claims (11)

a positive electrode and a negative electrode in which an electrode material is applied to a current collector;
a separator provided between the positive electrode and the negative electrode;
A tab is attached to each of the current collectors of the positive electrode and the negative electrode,
At least one of the positive electrode and the negative electrode has an impedance in the vicinity of the tab smaller than impedance in other regions ,
A secondary battery, wherein a portion is provided in the vicinity of the tab in which the coating ratio of the material for increasing the capacitance is higher than that of the other region . 2. The secondary battery of claim 1 , wherein the material that increases the capacitance is activated carbon. 2. The secondary battery in accordance with claim 1, wherein said separator has a thickness of 1 [mu]m or more and 100 [mu]m or less. 2. The secondary battery in accordance with claim 1, wherein said other region of said current collector is provided with a slit. 5. The secondary battery according to claim 4 , wherein said other region is divided into two by said slit. 2. The secondary battery in accordance with claim 1, wherein said other region of said current collector is provided with a through hole. 2. The secondary battery in accordance with claim 1, wherein an insulating plate is sandwiched between said tab of said positive electrode and said tab of said negative electrode. Having a configuration in which a plurality of secondary batteries according to claim 1 are connected in series,
A battery pack in which the tabs of two adjacent secondary batteries are connected. 9. The battery pack according to claim 8 , wherein said tab of said positive electrode and said tab of said negative electrode of said secondary battery are arranged with a space therebetween. a secondary battery according to claim 1;
an inverter;
a load connected to the inverter;
The electric power system, wherein a wire connecting the secondary battery and the inverter is shorter than a wire connecting another power supply device and the inverter. 11. The power system according to claim 10 , wherein said length of said wiring connecting said secondary battery and said inverter is 1 m or less.

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