JP2007042526A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery which can secure safety by controlling an electric corrosion of a battery case even at a time of over-discharge and a short circuit. <P>SOLUTION: A lithium ion secondary battery is composed of a battery can which is served as a negative electrode outer terminal and made of a nickel plated carbon steel and a group of electrodes of which positive/negative electrode plates are wound around a separator are housed in the above battery can. A negative electrode tab extended from the negative electrode plate is welded with an outer circumference of a negative electrode current collector ring placed below the group of electrodes. Below the negative electrode current collector ring, a negative electrode lead plate made of zinc which connects electrically the negative electrode plate with a battery can is welded and the negative lead plate is fixed with an inner bottom of the battery can by a resistance welding. An oxidation reduction potential of the negative electrode lead plate is set lower than that of the battery can. Even if a battery voltage becomes 0V due to a melting of the negative electrode lead plate, a negative electrode potential becomes lower than the oxidation reduction potential of the battery can. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery in which a positive and negative electrode plate is accommodated in a battery container that also serves as a negative electrode external terminal, and a steel material is used for the battery container.

  Conventionally, in the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have been mainstream. However, as electric devices have become smaller and lighter, lithium secondary batteries with high energy density have attracted attention, and research, development, and commercialization have progressed. At present, lithium secondary batteries for mobile phones and laptop computers are being used for small consumer applications. Secondary batteries are widely used.

  On the other hand, due to the problems of global warming and fuel depletion, each automobile manufacturer has developed an electric vehicle (EV) whose driving source is only an electric motor and a hybrid electric vehicle (HEV) where a part of driving is assisted by the electric motor. As a battery used for the power source, a battery having a higher capacity and a higher output has been demanded. As a power source that meets such requirements, a non-aqueous lithium secondary battery having a high voltage has attracted attention.

  In general, a large-sized lithium secondary battery used for a power source such as an EV or HEV is equipped with a voltage monitoring (control) device called a cell controller, and the charge / discharge voltage is controlled. Even if the cell controller breaks down and reaches an overcharged state, the lithium secondary battery is provided with a gas discharge mechanism and a current interruption mechanism, so that safety is maintained. In addition, when an overdischarge or a short circuit between positive and negative plates occurs, energy is released by the discharge, so that the amount of generated heat and the amount of gas generated are negligible, and no change in appearance is observed. In other words, even if the battery voltage becomes extremely low due to overdischarge, short circuit, etc., no dangerous state will be reached at that time, and sufficient safety is ensured even if a special mechanism is not provided for the battery. Yes. The safety of the battery here means that the battery behavior when the battery is exposed to an abnormal state does not cause damage to the human body, while minimizing damage to peripheral devices and vehicles. Means that.

  However, steel materials are usually used for battery containers of lithium secondary batteries. For this reason, if the battery is left for several days or weeks with the battery voltage extremely low at around 0V due to overdischarge or short circuit, the battery container will be electrically corroded and damaged. This may lead to leakage of the non-aqueous electrolyte. The amount of corrosion at this time is related to the battery capacity, and the possibility of electrical corrosion increases as the size of the battery increases for a power supply such as EV or HEV. In order to solve this, a technique using an aluminum alloy coated with a synthetic resin as a material of a battery container is disclosed (for example, see Patent Document 1). Further, a technique for forming a nickel plating layer containing a fluororesin fine powder having excellent corrosion resistance on the surface of an iron battery container is disclosed (for example, see Patent Document 2).

JP-A-8-167401 JP 2002-231195 A

  However, in the technique of Patent Document 1, although an aluminum alloy is coated with a synthetic resin, if the synthetic resin is not sufficiently coated and there is an exposed portion of the aluminum alloy, electrical corrosion may occur at that portion. Moreover, since it coat | covers with a synthetic resin, there exists a problem that material becomes expensive and it is hard to seal a battery container. Further, even in the technique of Patent Document 2, if there is an exposed portion of iron due to a crack or the like of the nickel plating layer, electrical corrosion will occur. In order to ensure the safety of the battery, it is important to suppress the electrical corrosion of the battery container and the leakage of the non-aqueous electrolyte when the battery is abnormal such as overdischarge or short circuit. Also, in the overdischarged state, there is no change in appearance and there is a possibility that electrical corrosion has occurred even if the leakage of the non-aqueous electrolyte does not reach, and the active material of the positive and negative electrodes may be deteriorated. It is also necessary to prevent such abnormal batteries from being reused.

  An object of the present invention is to provide a lithium secondary battery that can suppress electrical corrosion of a battery container and ensure safety even during overdischarge or short circuit.

  In order to solve the above-described problems, the present invention provides a lithium secondary battery in which a positive and negative electrode plate is accommodated in a battery container that also serves as a negative electrode external terminal, and a steel material is used for the battery container. A conductive lead made of metal that electrically connects the container, and the oxidation-reduction potential of the conductive lead is higher than the electrode reaction potential of the negative electrode plate and lower than the oxidation-reduction potential of the battery container. And

  In a lithium secondary battery capable of taking out negative electrode power from a battery container using steel, when a battery abnormality such as overdischarge or short circuit occurs, the lithium ion in the negative electrode plate is exhausted and the negative electrode potential reaches the positive electrode potential. Since the negative electrode potential reaches the oxidation-reduction potential of the battery container, the battery container is electrically corroded. In the lithium secondary battery of the present invention, since the oxidation-reduction potential of the metal energizing lead that electrically connects the negative electrode plate and the battery container is lower than that of the battery container, Since the current-carrying lead starts to melt at the oxidation-reduction potential, the negative electrode potential stops rising and the electrical corrosion of the battery container can be suppressed, and the current-carrying path between the negative electrode plate and the battery container is cut by melting the current-carrying lead. Since the function is lost, the safety of the abnormal battery can be ensured.

  In this case, if the current-carrying lead and the battery container are joined by resistance welding, the current-carrying lead of the joined part that has received the thermal history associated with resistance welding is likely to be dissolved by overdischarge or the like. The energization path can be cut reliably. Moreover, it is good also considering the material of a battery container as 1 type selected from nickel plating steel, nickel alloy plating steel, nickel clad steel, and nickel alloy clad steel. At this time, it is preferable that the material of the current-carrying lead is zinc or a zinc alloy.

  According to the present invention, since the oxidation-reduction potential of the current-carrying lead is lower than that of the battery container, even if the negative electrode potential increases due to battery abnormality, the current-carrying lead starts to dissolve at the oxidation-reduction potential of the current-carrying lead. In addition, the current path between the negative electrode plate and the battery container is cut by melting the current-carrying leads and the battery function is lost, so that the effect of ensuring the safety of abnormal batteries can be obtained. it can.

  Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, the cylindrical lithium ion secondary battery 20 of the present embodiment has a bottomed cylindrical battery can 16. In the present example, the battery can 16 is made of nickel-plated carbon steel with a thickness of 0.5 mm, and the dimensions are set to an outer diameter of 40 mm and a height of 100 mm.

  Inside the battery can 16 is accommodated an electrode group 15 in which a strip-shaped positive and negative electrode plate is wound around a spiral cylindrical cross-section through a separator on a hollow cylindrical shaft core 14 made of polypropylene. On the upper side of the electrode group 15, a positive electrode current collection ring 13 for collecting a potential from the positive electrode plate is disposed on a substantially extension line of the shaft core 14. The positive electrode current collecting ring 13 is fixed to the upper end portion of the shaft core 14. The edge of the positive electrode tab 2 led out from the positive electrode plate is joined to the periphery of the flange that integrally extends from the periphery of the positive electrode current collecting ring 13 by ultrasonic welding. A disc-shaped upper lid 12 that also serves as a positive electrode external terminal is disposed above the positive electrode current collecting ring 13. The upper lid 12 includes a safety valve 11 of an internal pressure reduction mechanism that releases gas when the pressure inside the battery reaches a predetermined pressure. The breaking (opening) pressure of the safety valve 11 is set to about 1 MPa. One end of a ribbon-like positive electrode lead made of aluminum is fixed to the upper portion of the positive electrode current collecting ring 13, and the other end of the positive electrode lead is joined to the lower surface of the upper lid 12 by welding.

  On the other hand, a negative electrode current collecting ring 17 for collecting a potential from the negative electrode plate is disposed below the electrode group 15. The outer peripheral surface of the lower end portion of the shaft core 1 is fixed to the inner peripheral surface of the negative electrode current collecting ring 17. The edge of the negative electrode tab 3 led out from the negative electrode plate is joined to the outer peripheral edge of the negative electrode current collecting ring 17 by ultrasonic welding. A negative electrode lead plate 18 serving as an energization lead for electrically connecting the negative electrode plate and the battery can 16 is disposed below the negative electrode current collecting ring 17.

  The negative electrode lead plate 18 has a disc shape and is formed with a recess capable of fixing the lower end portion of the shaft core 14 at a substantially central portion, and the material thereof is zinc or galvanized steel. The oxidation-reduction potentials of zinc and galvanized steel used for the negative electrode lead plate 18 are 2.30 V (vs. Li) and 2.35 V (vs. Li), respectively. Since the redox potential of iron, which is the main component of carbon steel used for the battery can 16, is about 2.7 V (vs. Li), the redox potential of the negative electrode lead plate 18 is set lower than that of the battery can 16. . In the lithium ion secondary battery 20, since the electrode reaction potential of the negative electrode plate is 0.1 to 1.0 V (vs. Li), the oxidation-reduction potential of the negative electrode lead plate 18 is set higher than the electrode reaction potential of the negative electrode plate. Has been. The upper surface of the negative electrode lead plate 18 is joined to the lower surface of the negative electrode current collecting ring 17 by resistance welding, and the lower surface of the recess is joined to the inner bottom surface of the battery can 16 by resistance welding. For this reason, since the battery can 16 is electrically connected to the negative electrode plate via the negative electrode lead plate 18 and the negative electrode current collecting ring 17, the negative electrode power can be taken out from the battery can 16 also serving as the negative electrode external terminal. is there.

The upper lid 12 is caulked and fixed to the upper part of the battery can 16 via an insulating and heat resistant resin gasket. The positive electrode lead is accommodated in a battery can 16 so as to be folded, and the lithium ion secondary battery 20 is sealed. Further, a non-aqueous electrolyte (not shown) is injected into the battery can 16. Non-aqueous electrolyte includes hexafluorophosphoric acid as lithium salt (electrolyte) in a mixed organic solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) in a volume ratio of 1: 1: 1. lithium (LiPF ₆₎ which was dissolved 1 mol / l is used.

  In the electrode group 15, the positive electrode plate and the negative electrode plate are wound around the shaft core 14 with a separator of a microporous polyethylene film having a thickness of 40 μm so that the two electrode plates do not directly contact each other. The positive electrode lead piece 2 and the negative electrode lead piece 3 are arranged on both end surfaces of the electrode group 15 opposite to each other. Insulation coating is applied to the entire circumference of the collar surface of the electrode group 15 and the positive electrode current collector ring 13.

The positive electrode plate constituting the electrode group 15 uses lithium manganate (LiMn ₂ O ₄ ), which is a typical lithium manganese complex oxide, as the positive electrode active material. A positive electrode mixture containing lithium manganate is applied substantially uniformly on both surfaces of an aluminum foil (positive electrode current collector). The thickness of the aluminum foil is set to 20 μm in this example. In the positive electrode mixture, for example, 10 parts by weight of scaly graphite as a conductive material and polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder) with respect to 90 parts by weight of lithium manganate. 5 parts by weight is blended. When the positive electrode mixture is applied to the aluminum foil, the viscosity is adjusted with N-methylpyrrolidone (hereinafter abbreviated as NMP) as a dispersion solvent. The positive electrode plate is dried and then pressed and cut.

  On the other hand, the negative electrode plate uses an amorphous carbon powder of a carbon material as a negative electrode active material. A negative electrode mixture containing amorphous carbon powder is applied substantially uniformly on both sides of a rolled copper foil (negative electrode current collector). In this example, the thickness of the rolled copper foil is set to 10 μm. For example, 10 parts by weight of PVDF as a binder is blended with 90 parts by weight of amorphous carbon powder in the negative electrode mixture. When the negative electrode mixture is applied to the rolled copper foil, the viscosity is adjusted with the dispersion solvent NMP. The negative electrode plate is pressed and cut after being dried.

  Uncoated portions of the positive electrode mixture and the negative electrode mixture are formed on the side edges on one side in the longitudinal direction of the aluminum foil and the rolled copper foil, respectively. Uncoated portions are cut out at equal intervals and in a rectangular shape (comb shape), and strip-like positive electrode tabs 2 and negative electrode tabs 3 are formed at the remaining portions of the cutouts. The negative electrode plate is slightly wider than the positive electrode plate.

(Action etc.)
The operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  Generally, the electrode reaction potential of the negative electrode in a lithium ion secondary battery is 0.1 to 1.0 V (vs. Li). However, when the battery voltage decreases to near 0V due to overdischarge or short circuit, the negative electrode potential may increase to about 3V (vs. Li). That is, in the discharge reaction of the lithium ion secondary battery, lithium is released as ions from the carbon material, which is the negative electrode active material, into the non-aqueous electrolyte, and the lithium ions in the non-aqueous electrolyte are taken into the positive electrode active material. I'm stuck. Although slightly different depending on the active material used for the positive and negative electrodes, in the overdischarged state, the amount of lithium ions in the negative electrode plate is exhausted first and rises to the positive electrode potential (the positive electrode potential hardly changes). For this reason, when a steel material mainly composed of iron is used for the battery can, since the iron redox potential is about 2.7 V (vs. Li), the iron is dissolved and the electric corrosion of the battery can occurs. . Even when using steel materials whose surfaces are plated with nickel, or clad materials of steel materials and nickel materials, it is only necessary to cover the iron surface reliably. If there is an exposed part, corrosion may occur. When corrosion increases, the battery can is damaged and the non-aqueous electrolyte leaks. The lithium ion secondary battery 20 of the present embodiment solves these problems.

  In the lithium ion secondary battery 20 of the present embodiment, carbon steel with nickel plating applied to the material of the battery can 16 is used, and the negative electrode lead plate 18 that electrically connects the negative electrode plate and the battery can 16 is used. Zinc and galvanized steel are used as the material. Since the oxidation-reduction potentials of zinc and galvanized steel are 2.30 and 2.35 V (vs. Li), respectively, the oxidation-reduction potential of the negative electrode lead plate 18 is the oxidation-reduction potential 2 of iron, which is the main component of carbon steel. It is set lower than 0.7V (vs. Li). For this reason, when the negative electrode potential rises due to overdischarge or the like and reaches the oxidation-reduction potential of the negative electrode lead plate 18, the negative electrode lead plate 18 starts to dissolve. As a result, the increase in the negative electrode potential stops at the oxidation-reduction potential of the negative electrode lead plate 18, and lithium ions contained in the non-aqueous electrolyte take up in the positive electrode active material by the amount corresponding to the dissolved amount of the negative electrode lead plate 18. Therefore, the positive electrode potential is lowered, and the battery voltage becomes 0 V at the redox potential (dissolution potential) of the negative electrode lead plate 18. Therefore, even if the battery voltage becomes 0V due to the dissolution of the negative electrode lead plate 18, the negative electrode potential becomes lower than 2.7V (vs. Li). Corrosion can be suppressed.

  Further, since the connection between the negative electrode plate and the battery can 16 is cut by the dissolution of the negative electrode lead plate 18, the battery can 16 becomes electrically neutral, not only causing no electrical corrosion but also being unusable as a battery. . For this reason, it is possible to prevent an abnormal battery that has been overdischarged or short-circuited from being reused, and to ensure the safety of the battery.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the negative electrode lead plate 18 is joined to the inner bottom surface of the battery can 16 by resistance welding. In resistance welding, since welding is performed by heat generated by resistance between metals generated by bringing a metal into contact with each other and flowing current, the negative electrode lead plate 18 receives a thermal history during joining. For this reason, since the part which received the thermal history becomes easy to selectively melt | dissolve, between a negative electrode plate and the battery can 16 will be cut | disconnected rapidly at the time of battery abnormality, and safety | security can be ensured.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the redox potential of the negative electrode lead plate 18 is set higher than the electrode reaction potential of the negative electrode plate of 0.1 to 1.0 V (vs. Li). For this reason, since the negative electrode potential does not reach the oxidation-reduction potential of the negative electrode lead plate 18 during normal charge / discharge, the negative electrode lead plate 18 can be charged / discharged without melting, and battery performance can be exhibited. .

  In the present embodiment, carbon steel in which the material of the battery can 16 is nickel-plated is exemplified, but the present invention is not limited to this, and for example, carbon steel itself or a special material containing elements such as chromium The present invention can be applied to a lithium ion secondary battery in which a steel material mainly composed of iron such as steel is used for the battery can 16. Further, it has been confirmed that the same effect is obtained when a clad material of nickel and carbon steel is used, and even if a nickel alloy is used instead of nickel, there is no difference in the effect. By using one kind selected from nickel-plated steel, nickel alloy-plated steel, nickel / steel clad material and nickel alloy / steel clad material, the corrosion resistance of the material itself is higher than that of carbon steel alone. Since it becomes high, it can make it easy to suppress the electrical corrosion of a battery can. Furthermore, although the example where the shape of the battery can 16 is cylindrical has been shown, the present invention is not limited to the shape of the battery can, and may be a shape such as a square. In the present embodiment, the electrode group 15 in which the positive and negative electrode plates are wound is illustrated, but the present invention can be applied to an electrode group in which the positive and negative electrode plates are laminated.

  In the present embodiment, zinc and galvanized steel are exemplified as the material of the negative electrode lead plate 18, but the present invention is not limited to this. The material of the negative electrode lead plate 18 may be any material as long as the oxidation-reduction potential is higher than the electrode reaction potential of the negative electrode plate and lower than the oxidation-reduction potential of the battery can 16. What is necessary is just to select according to a material. Furthermore, the size of the negative electrode lead plate 18 is not particularly limited. However, the amount of electrical corrosion of the battery can caused by overdischarge increases as the battery capacity increases, and therefore, it may be set in consideration of the battery capacity. Further, in the present embodiment, an example in which the negative electrode side electrical connection is as follows: negative electrode plate → negative electrode current collecting ring 17 → negative electrode lead plate 18 → battery can 16 is shown. This is because when the lithium ion secondary battery 20 of the present embodiment is used, for example, as a power source for an electric vehicle, even if a large current is applied at the time of starting or accelerating the electric vehicle, In order to avoid the occurrence of a drop (IR drop), the negative electrode current collecting ring 17 is connected.

Furthermore, in the present embodiment, an example in which LiPF ₆ is a lithium salt (electrolyte) and a mixed organic solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate is used as the organic solvent in the nonaqueous electrolytic solution is described. The organic solvent is not particularly limited, and any commonly used nonaqueous electrolytic solution may be used. In addition, although examples in which lithium manganate is used as the positive electrode active material and amorphous carbon is used as the negative electrode active material have been shown, these materials are not particularly limited.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
As shown in Table 1 below, in Example 1, the negative electrode lead plate 18 was made of zinc having a redox potential of 2.30 V (vs. Li), and a lithium ion secondary battery 20 having a capacity of 4.0 Ah was produced. .

(Example 2)
As shown in Table 1, in Example 2, the negative electrode lead plate 18 was made of galvanized steel having a redox potential of 2.35 V (vs. Li), and a lithium ion secondary battery 20 having a capacity of 4.0 Ah was produced. did.

(Comparative Example 1)
As shown in Table 1, in Comparative Example 1, a lithium ion secondary battery having a capacity of 4.0 Ah was manufactured using nickel having a redox potential of 3.90 V (vs. Li) as the material of the negative electrode lead plate.

<Test and evaluation>
About each battery of an Example and a comparative example, after leaving for 30 days in the state over-discharged to 0V, the battery was decomposed | disassembled, the negative electrode potential was measured, and the corrosion condition of the battery can 16 was observed visually. Table 1 also shows the measurement results of the negative electrode potential and the observation results of the corrosion status.

  As shown in Table 1, Example 1 using zinc with a redox potential of 2.30 V (vs. Li) for the negative electrode lead plate 18 and galvanized steel with a redox potential of 2.35 V (vs. Li) were used. In the lithium ion secondary battery 20 of Example 2, even when the battery voltage was 0 V, the negative electrode potential was lower than the dissolution potential of iron 2.70 V, and corrosion of the battery can 16 was not observed. On the other hand, in the lithium ion secondary battery of Comparative Example 1 using nickel having a redox potential of 3.90 V (vs. Li) for the negative electrode lead plate, the negative electrode potential reached 2.70 V, and the corrosion of the battery can was reduced. Was observed. Moreover, in the lithium ion secondary battery 20 of Example 1 and Example 2, since the negative electrode lead plate 18 melt | dissolved, it was confirmed that the electrical connection of a negative electrode plate and the battery can 16 is cut | disconnected. In contrast, in the lithium ion secondary battery of Comparative Example 1, dissolution of the negative electrode lead plate 18 was not observed.

  From the above results, the negative electrode plate and the battery can 16 were electrically connected to each other by the negative electrode lead plate 18 using zinc and zinc-plated steel each having a lower oxidation-reduction potential than the nickel-plated steel used as the material of the battery can. In the case of Example 1 and Example 2, it was found that the corrosion of the battery can 16 can be suppressed even when the battery voltage becomes 0V. Further, it has been confirmed that the negative electrode lead plate 18 does not melt during normal charging / discharging of the lithium ion secondary battery 20. This is because the electrode reaction potential of the negative electrode is 0.1 to 1.0 V (vs. Li) during normal charge and discharge, and thus the oxidation-reduction potential of the negative electrode lead plate 18 is higher than the electrode reaction potential of the negative electrode. Conceivable.

  Further, even in the lithium ion secondary battery of Comparative Example 1 in which the corrosion of the battery can was observed, no leakage of the non-aqueous electrolyte was observed, so there was no change in appearance and the battery could be reused if charged. . However, in reality, the battery can is corroded, and the negative electrode active material is considered to be deteriorated. Therefore, it is preferable to avoid reuse in consideration of safety, but the appearance cannot be determined. On the other hand, in the lithium ion secondary battery 20 of Example 1 and Example 2, since the electrical connection between the negative electrode plate and the battery can 16 was cut by the dissolution of the negative electrode lead plate 18, it could not be charged. It could not be reused. Therefore, in the lithium ion secondary battery 20 of Example 1 and Example 2, there is no leakage of the non-aqueous electrolyte, the reuse of the abnormal battery can be avoided, and the battery is excellent in safety. found.

  Since the present invention contributes to the manufacture and sale of lithium secondary batteries in order to provide a lithium secondary battery that can prevent electrical corrosion of the battery container and ensure safety even during overdischarge or short circuit, With the availability of

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment to which this invention is applied.

Explanation of symbols

3 Negative electrode tab 12 Upper lid 15 Electrode group 16 Battery can (battery container)
17 Negative current collector ring 18 Negative electrode lead plate (conductive lead)
20 Lithium secondary battery

Claims (4)

  In a lithium secondary battery in which a positive and negative electrode plate is housed in a battery container that also serves as a negative electrode external terminal, and a steel material is used for the battery container, a metal energization that electrically connects the negative electrode plate and the battery container A lithium secondary battery comprising a lead, wherein a redox potential of the conducting lead is higher than an electrode reaction potential of the negative electrode plate and lower than a redox potential of the battery container.   The lithium secondary battery according to claim 1, wherein the energization lead and the battery container are joined by resistance welding.   3. The lithium secondary according to claim 1, wherein a material of the battery container is one selected from nickel plated steel, nickel alloy plated steel, nickel clad steel, and nickel alloy clad steel. battery.   The lithium secondary battery according to claim 3, wherein a material of the energization lead is zinc or a zinc alloy.

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