Method of manufacturing an electrode for an energy storage device

Abstract

An electrode for an energy storage device including a Zn layer or Zn alloy layer, a Ni layer, and a Sn layer or Sn alloy layer formed by plating on a connecting terminal part of a positive electrode composed of Al so that the resistance value at the contacting point is reduced and the voltage of the energy storage device can be effectively supplied without any drop. Accordingly, this electrode can be soldered to a Cu negative electrode, which is composed of metal that is different species from Al, through a Sn layer or a Sn alloy layer so that jointing strength of the Al positive electrode and the Cu negative electrode can be enhanced. The contacting area is increased in comparison with the conventional jointing by spot-welding or conventional fastening by a bolt so that the resistance value at the contacting point is reduced.

Claims

1. A method of manufacturing an electrode for an energy storage device, the method comprising: degreasing a surface of a positive electrode containing Al by using an organic solvent; thereafter, etching the surface of the positive electrode degreased in the step of degreasing, by using an etchant; thereafter, forming a Zn plating on the surface of the positive electrode etched in the step of etching, by using a liquid zincate; thereafter, forming a Ni plating on a surface of the Zn plating formed in the step of forming a Zn plating, by using a Ni plating solution; and thereafter, forming a Sn plating on a surface of the Ni plating formed in the step of forming a Ni plating, by using a Sn plating solution.

2. The method of manufacturing an electrode for an energy storage device according to claim 1 wherein the step of forming a Zn plating on the surface of the positive electrode by using a liquid zincate is performed at least two times.

3. The method of manufacturing an electrode for an energy storage device according to claim 2 wherein the step of forming a Zn plating on the surface of the positive electrode by using a liquid zincate includes forming a layer of Zn or Zn alloy having a thickness of 0.05 through 0.1 m.

4. The method of manufacturing an electrode for an energy storage device according to claim 1 wherein the step of forming a Zn plating on the surface of the positive electrode by using a liquid zincate includes forming a layer of Zn or Zn alloy having a thickness of 0.05 through 0.1 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of energy storage device 100 according to this invention showing a configuration example thereof.

(2) FIG. 2 is a cross sectional view of plating layers 20 for showing a configuration example thereof.

(3) FIG. 3 is a perspective view of the energy storage device 100 for showing a connecting example thereof.

(4) FIG. 4 is a set of photographs showing the results of an environmental test.

(5) FIG. 5 is a diagram showing characteristics example relating to resistance value of jointed samples.

(6) FIG. 6 is a diagram showing characteristics example relating to voltage value of the jointed samples.

(7) FIG. 7 is a diagram showing characteristics example relating to temperature of the jointed samples.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(8) The following will describe energy storage device according to this invention such as electric double layer capacitor, lithium ion capacitor and secondary battery with reference to the drawings.

(9) [Configuration Example of Energy Storage Device 100]

(10) First, the following will describe a configuration example of an energy storage device 100 according to this invention. As shown in FIG. 1, the energy storage device 100 is composed of a lead electrode in a positive electrode composed of Al (hereinafter, referred to as Al positive electrode 10), a lead electrode in a negative electrode composed of Cu (hereinafter, referred to as Cu negative electrode 30), which is different species from Al, and a separator 40.

(11) The Al positive electrode 10 and the Cu negative electrode 30 are respectively provided with connecting terminal parts 10a, 30a extending from their ends. Regarding the connecting terminal parts 10a, 30a, when connecting the energy storage devices 100 in series, the connecting terminal part 10a and the connecting terminal part 30a are connected to each other, whereas when connecting the energy storage devices 100 in parallel, the connecting terminal parts 10a are connected to each other or the connecting terminal parts 30a are connected to each other. Further, the connecting terminal parts 10a, 30a are also external connecting terminals when they do not connect the energy storage devices 100 in series nor in parallel.

(12) Plating layers 20 are formed on the connecting terminal part 10a. The plating layers 20 are formed in order to connect the connecting terminal part 10a and the connecting terminal part 30a easily and surely.

(13) [Configuration Example of Plating Layers 20]

(14) As shown in FIG. 2, the plating layers 20 are formed so that the Zn layer 21, the Ni layer 22, and the Sn layer 23 are formed on the connecting terminal part 10a composed of Al by plating. It is to be noted that Zn layer 21 may be Zn alloy layer and Sn layer 23 may be Sn alloy layer. For example, Zn alloy layer is ZnNi alloy, ZnFe alloy, ZnAl alloy or the like and Sn alloy layer is SnBi alloy, SnAg alloy, SnCu alloy or the like.

(15) Thicknesses of the Zn layer 21, the Ni layer 22, and the Sn layer 23 exert an influence on reliability of the connection of the Al positive electrode 10 and the Cu negative electrode 30. When the thickness of the Zn layer 21 is 0.01 m or less, the Ni layer 22 is hard to be formed on the Zn layer 21, whereas when the thickness of the Zn layer 21 is 0.15 m or more, adhesiveness between the connecting terminal part 10a of Al and the Zn layer 21 becomes poor so that this portion may be peeled off. It is preferable that the thickness of the Zn layer 21 is 0.05 through 0.1 m.

(16) Further, when plating the Zn layer 21, alkaline bath is suitable for enhancing the adhesiveness to the connecting terminal part 10a of Al. For example, zincate bath in which ZnO, Zn, NaOH and the like are dissolved by water or cyanide bath in which cyanide such as NaCN is added to the zincate bath are suitable therefor. The plating based on the zincate bath or the cyanide bath is less effective by only once because a surface of the connecting terminal part 10a of Al is subject to oxidation so that the processes by two times or more are required.

(17) Regarding the Ni layer 22, when the thickness of the Ni layer 22 is too thin, a barrier effect between the Zn layer 21 and the Sn layer 23 is lost whereas when it is too thick, the Ni layer 22 and the Cu negative electrode 30 are reacted when soldering so that any intermetallic compounds such as Cu.sub.3Sn and Cu.sub.6Sn.sub.5 are formed. Since the intermetallic compounds such as Cu.sub.3Sn and Cu.sub.6Sn.sub.5 are hard and breakable, they are suitable for any electrodes. Accordingly, it is preferable that the thickness of the Ni layer 22 is 1 through 3 m, more preferably, 2 through 3 m.

(18) Regarding the Sn layer 23, when the thickness of the Sn layer 23 is too thin, Ni in the Ni layer 22 is oxidized so that solderability to the Cu negative electrode 30 becomes poor whereas when it is too thick, a portion of the Sn layer 23 is easy to be broken when performing folding on the Al positive electrode 10. Accordingly, it is preferable that the thickness of the Sn layer 23 is 5 through 15 m.

(19) [Connecting Example of Energy Storage Devices 100]

(20) Next, the following will describe a connecting example of the energy storage devices 100. As shown in FIG. 3, when connecting the energy storage devices 100 in series, their connecting terminal parts 10a and their connecting terminal parts 30a are connected to each other through the plating layers 20 and solder 50. The solder 50 is hard to solder Al of the connecting terminal part 10a but is easy to solder the connecting terminal parts 30a of Cu and the plating layers 20. By the way, the solder 50 may be leaded solder or lead-free solder composed of SnAgCu or SnZn.

(21) Accordingly, since the Al positive electrode 10 and the Cu negative electrode 30 can be soldered through the plating layers 20, jointing strength between the Al positive electrode 10 and the Cu negative electrode 30 can be enhanced. Further, since the contacting area between the connecting terminal part 10a and the connecting terminal part 30a is increased in comparison with the conventional jointing by the spot-welding or the conventional fastening by a bolt so that the resistance value at the contacting point (referred to as a point by which the connecting terminal part 10a and the connecting terminal part 30a are contacted) is reduced, the voltage drop of the energy storage device 100 by contact resistance can be reduced. As a result thereof, it is possible to supply the voltage of the energy storage device 100 effectively to a load without any drop of the voltage thereof.

(22) Additionally, although the negative electrode composed of Cu has been described in this embodiment, this invention is not limited thereto: This invention is applicable for any negative electrodes of metal which is different species from Al.

Embodiment 1

(23) Next, the following will describe a manufacturing method of the plating layers 20 formed on the Al positive electrode 10 of the energy storage device 100 according to this invention. The plating layers 20 are manufactured according to the following procedures 1 through 5.

(24) <1. Degreasing Step>

(25) The connecting terminal part 10a having a dimension of a length of 70 mm, a width of 50 mm, and a thickness of 0.2 mm is dipped and degreased by using organic solvent.

(26) <2. Etching Step>

(27) The degreased connecting terminal part 10a is washed by water and alkali-etched and then, is dipped into acid solution (etchant) so that its surface is made rough. By this step, the connecting terminal part 10a composed of Al and the Zn layer 21 are favorably adhered closely to each other.

(28) <3. Zn Plating Step>

(29) The etched connecting terminal part 10a is dipped into zincate bath in which ZnO, Zn, NaOH and the like are dissolved with water to form Zn plating (Zn layer 21).

(30) In order to wash liquid zincate adhered to Zn-plated connecting terminal part 10a, it is washed by water and the connecting terminal part 10a is then dipped into nitric acid to peel off the zincate (Zn and the like).

(31) Again, the connecting terminal part 10a is dipped into the zincate bath to form Zn plating and after it is washed by water, it is dipped into the nitric acid to peel off the zincate (Zn and the like).

(32) It is to be noted that in a case where ZnNi alloy plating is formed in place of the above-mentioned Zn plating, zincate bath in which ZnCl.sub.2, NiCl.sub.2 and the like are added to the zincate bath is used.

(33) <4. Ni Plating Step>

(34) The connecting terminal part 10a on which the Zn plating has been formed is dipped into electroless Ni plating bath in which NiSO.sub.4.6H.sub.2O, NaH.sub.2PO.sub.4 and the like are dissolved with water for about 300 seconds to form Ni plating (Ni layer 22) and is washed by water. It is to be noted that Ni plating is not limited to the electroless plating, it may use any electroplating.

(35) <5. Sn Plating Step>

(36) The connecting terminal part 10a on which the Ni plating has been formed is dipped into alkaline or acidic Sn plating bath in which Na.sub.2SO.sub.3.3H.sub.2O, Sn, NaOH.sub.2 and the like are dissolved with water for about 20 minutes to form Sn plating (Sn layer 23) and is washed by water. It is then dried to complete the plating layers 20.

(37) The film thickness of each of the plating layers 20 manufactured according to the above-mentioned steps 1 through 5 was measured by an X-ray fluorescence film thickness gauge, so that a thickness of Zn layer 21 was 0.05 m, a thickness of Ni layer 22 was 1.5 m, and a thickness of Sn layer 23 was 7 m.

Embodiment 2

(38) The Al positive electrode 10 having the plating layers 20 formed by the first embodiment and the Cu negative electrode 30 are soldered to each other using resin flux cored solder. As the resin flux cored solder, RMA08 (manufactured by SENJU METAL INDUSTRY Co., LTD) is used, and it is soldered under a condition such that temperature of a tip of soldering iron is 300 degrees C. and a period of time for soldering is 10 seconds.

(39) As a comparison example 1, it is made such that Al positive electrode and Cu negative electrode are directly soldered by wire solder composed of Sn-15Zn (mass %). Incidentally, in this soldering, the soldering is carried out with flux being used.

(40) As a comparison example 2, it is made such that Al positive electrode and Cu negative electrode are connected to each other by the spot-welding using ultrasonic wave.

(41) In Table 1, a measured result of jointing strength of the Al positive electrode and the Cu negative electrode in each of the embodiment 1 and the comparison examples 1 and 2 is shown. By the way, this jointing strength was measured by an adhesive strength tester based on JIS H8630 and JIS C6481 (numbers of samples are 5). Further, jointing strength thereof after the samples are oxidized acceleratingly was measured. The oxidation acceleration condition was such that the samples were positioned into a thermostat oven having ambience temperature of 85 degrees C. and humidity of 85% for 24 hours and an electric current of 100 A in which ON/OFF were repeated every second flowed through the samples.

(42) TABLE-US-00001 TABLE 1 JOINTING STRENGTH (kg/cm) BEFORE AFTER OXIDATION OXIDATION DIFFER- ACCELERATION ACCELERATION ENCE EMBODYMENT 5.9 4.5 1.4 1 COMPARISON 5.3 3.8 1.5 EXAMPLE 1 COMPARISON 2.9 0.71 2.19 EXAMPLE 2

(43) As shown in Table 1, the jointing strength before the oxidation acceleration of the embodiment 1 was 5.9 kg/cm; that of the comparison example 1 was 5.3 kg/cm; and that of the comparison example 2 was 2.9 kg/cm. Thus, it is seen that the jointing strength of embodiment 1 is enhanced over those of the comparison examples 1 and 2.

(44) The jointing strength after the oxidation acceleration of the embodiment 1 was 4.5 kg/cm; that of the comparison example 1 was 3.8 kg/cm; and that of the comparison example 2 was 0.71 kg/cm. Thus, it is seen that the jointing strength of embodiment 1 is enhanced over those of the comparison examples 1 and 2 even after the oxidation acceleration.

(45) The difference between the jointing strengths before and after the oxidation acceleration of the embodiment 1 is 1.4 kg/cm; that of the comparison example 1 was 1.5 kg/cm; and that of the comparison example 2 was 2.19 kg/cm. Thus, it is seen that the difference between the jointing strengths before and after the oxidation acceleration in embodiment 1 is smaller than those of the comparison examples 1 and 2 and the jointing reliability thereof is improved.

(46) FIG. 4 shows photographically a result of an environmental test when salt water is sprayed onto the embodiment 1 and the comparison examples 1 and 2 is shown (conditions of the Al positive electrode and the Cu negative electrode after 120 hours and 600 hours from a start of the test). By the way, this environmental test is based on JIS C0024.

(47) As shown in FIG. 4, pitting corrosion and white powder do not occur in the embodiment 1 after 120 hours from the start of test but a small amount of white powders occurs in the embodiment 1 after 600 hours. Pitting corrosion occurs in the comparison example 1 after 120 hours from the start of test and a large amount of white powders occurs in the comparison example 1 after 600 hours. White powder occurs in the comparison example 2 after 120 hours from the start of test and a large amount of white powders occurs in the comparison example 2 after 600 hours. Thus, the occurrence of pitting corrosion and/or the occurrence of a large amount of white powders cause electric conductivity and/or strength of the electrode for energy storage device to be deteriorated.

(48) Accordingly, in the embodiment 1, no pitting corrosion occur and only a small amount of white powders such that any influence is not exerted upon the electric conductivity and/or the strength occurs. In other words, it is seen that the embodiment 1 has good electric conductivity and has reliability as energy storage device. It, however, is seen that the comparison examples 1 and 2 have poor electric conductivity under an environment of the sprayed salt water so that they have poor reliability as energy storage device.

Embodiment 3

(49) Jointed samples were made by the Al positive electrode and the Cu negative electrode of the embodiment 1 and the comparison examples 1 and 2 and resistance value and voltage value of the jointed sample thus made were measured by a microohm meter using Kelvin clips according to four-terminal method. This measurement condition was such that the samples of the embodiment 1 and the comparison examples 1 and 2 were put into a thermostat oven having ambience temperature of 85 degrees C. and humidity of 85% and an electric current of 100 A in which ON/OFF were repeated every second flowed through the samples.

(50) FIG. 5 is a diagram showing characteristics example relating to resistance value of the jointed samples in which a vertical axis indicates resistance value () of the jointed samples and a horizontal axis indicates repeated frequency (1000) on ON/OFF of electric current of 100 A. As shown in FIG. 5, the resistance values of the jointed sample in the embodiment 1 are shown as diamond-wise points. Its value was 400 at its initial state, was 440 after 24000 times of ON/OFF, was 450 after 48000 times of ON/OFF, was 450 after 75000 times of ON/OFF, and was 470 after 120000 times of ON/OFF. The resistance values of the jointed sample in the comparison example 1 are shown as square-wise points. Its value was 330 at its initial state, was 360 after 24000 times of ON/OFF, was 400 after 48000 times of ON/OFF, was 500 after 75000 times of ON/OFF, and was 600 after 120000 times of ON/OFF. The resistance values of the jointed sample in the comparison example 2 are shown as triangle-wise points. Its value was 575 at its initial state, was 600 after 24000 times of ON/OFF, was 600 after 48000 times of ON/OFF, was 670 after 75000 times of ON/OFF, and was 750 after 120000 times of ON/OFF.

(51) Accordingly, the resistance value of the embodiment 1 after 120000 times of ON/OFF indicates the resistance value of merely 60% though 80% of the resistance values of the comparison examples 1 and 2. Accordingly, the embodiment 1 can reduce electric loss up to about 60% though 80% thereof.

(52) Further, the resistance values of the jointed sample in the embodiment 1 change to merely about 70 from the initial state thereof to after 120000 times of ON/OFF whereas the resistance values of the jointed sample in the comparison example 1 change even to 270 as well as the resistance values of the jointed sample in the comparison example 2 change even to 175. Namely, the reliability of the embodiment 1 is more improved than those of the comparison examples 1 and 2.

(53) FIG. 6 is a diagram showing characteristics example relating to voltage value of the jointed samples in which a vertical axis indicates the voltage value (V) applied to the jointed samples and a horizontal axis indicates repeated frequency (1000) on ON/OFF of electric current of 100 A. As shown in FIG. 6, the voltage values of the jointed sample in the embodiment 1 are shown as diamond-wise points. Its value was constant at 0.2 V from its initial state up to after 120000 times of ON/OFF. The voltage values of the jointed sample in the comparison example 1 are shown as square-wise points. Its value was 0.2 V at its initial state, was 0.2 V after 24000 times of ON/OFF, was 0.3 V after 48000 times of ON/OFF, was 0.4 V after 75000 times of ON/OFF, and was 0.5 V after 120000 times of ON/OFF. The voltage values of the jointed sample in the comparison example 2 are shown as triangle-wise points. Its value was 0.7 V at its initial state, was 0.7 V after 24000 times of ON/OFF, was 0.8 V after 48000 times of ON/OFF, was 0.8 V after 75000 times of ON/OFF, and was 0.8 V after 120000 times of ON/OFF.

(54) Thus, in the embodiment 1, the voltage values of jointed sample remain unchanged even after 120000 times of ON/OFF, which allows its reliability to be more improved than those of the comparison examples 1 and 2.

Embodiment 4

(55) Jointed samples were made by the Al positive electrode and the Cu negative electrode of the embodiment 1 and the comparison examples 1 and 2 and temperatures of the jointed samples thus made were measured by a thermocouple of K type. This measurement condition was similar to that shown in the embodiment 3 and was such that the samples of the embodiment 1 and the comparison examples 1 and 2 were put into a thermostat oven having ambience temperature of 85 degrees C. and humidity of 85% and an electric current of 100 A in which ON/OFF were repeated every second flowed through the samples.

(56) FIG. 7 is a diagram showing characteristics example relating to temperature of the jointed samples in which a vertical axis indicates the temperature (degrees C.) of the jointed samples and a horizontal axis indicates repeated frequency (1000) on ON/OFF of electric current of 100 A. As shown in FIG. 7, the temperatures of the jointed sample in the embodiment 1 are shown as diamond-wise points. Its value was 85.55 degrees C. at its initial state, was 85.55 degrees C. after 24000 times of ON/OFF, was 85.55 degrees C. after 48000 times of ON/OFF, was 85.77 degrees C. after 75000 times of ON/OFF, and was 85.77 degrees C. after 120000 times of ON/OFF. The temperatures of the jointed sample in the comparison example 1 are shown as square-wise points. Its value was 84.22 degrees C. at its initial state, was 84.28 degrees C. after 24000 times of ON/OFF, was 85.11 degrees C. after 48000 times of ON/OFF, was 87.9 degrees C. after 75000 times of ON/OFF, and was 90.52 degrees C. after 120000 times of ON/OFF. The temperatures of the jointed sample in the comparison example 2 are shown as triangle-wise points. Its value was 96.3 degrees C. at its initial state, was 96.89 degrees C. after 24000 times of ON/OFF, was 96.06 degrees C. after 48000 times of ON/OFF, was 97.3 degrees C. after 75000 times of ON/OFF, and was 97.3 degrees C. after 120000 times of ON/OFF. These temperature changes are resulted from any changes in the resistance values of the jointed samples and any changes in Joule heat.

(57) Thus, in the embodiment 1, the temperature of the jointed sample remain unchanged even after 120000 times of ON/OFF (because the resistance value of the jointed sample shown in FIG. 5 is low), which allows its reliability to be more improved than those of the comparison examples 1 and 2.

(58) Thus, in the energy storage device 100 according to this invention, the Zn layer 21, the Ni layer 22, and the Sn layer 23 are formed on the Al positive electrode 10 by plating. Accordingly, it is possible to solder the positive electrode to the Cu negative electrode 30 composed of Cu, which is different metal from Al, through Sn layer 23. As a result thereof, jointing strength between the Al positive electrode 10 and the Cu negative electrode 30 can be enhanced.

(59) Further, in the energy storage device 100, since a contacting area between the connecting terminal part 10a and the connecting terminal part 30a is increased in comparison with the conventional jointing by soldering (comparison example 1) or the conventional jointing by the spot-welding using ultrasonic wave (comparison example 2) and the conventional fastening by a bolt so that the resistance value at the contacting point is reduced, the voltage drop of the energy storage device 100 by the contact resistance can be reduced. As a result thereof, it is possible to supply the voltage of the energy storage device 100 to a load effectively without any drop of the voltage thereof.

INDUSTRIAL APPLICABILITY

(60) The energy storage device according to this invention is not limited to box-like one: it is applicable to energy storage device of cylinder type such as electric double layer capacitor, lithium ion capacitor and secondary battery.

EXPLANATION OF CODES

(61) 10: Al Positive Electrode 10a, 30a: Connecting Terminal Parts 20: Plating Layers 21: Zn Layer 22: Ni Layer 23: Sn Layer 30: Cu Negative Electrode 40: Separator 50: Solder 100: Energy Storage Device