JP5250466B2 - Non-aqueous electrolyte secondary battery and lithium secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a lithium secondary battery.

  In the field of rechargeable secondary batteries, non-aqueous electrolysis with high energy density in addition to batteries using aqueous electrolyte such as lead batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. Batteries using liquids have attracted attention. A battery using a non-aqueous electrolyte has a high energy density and is suitable for reducing the size and weight of electrical equipment. Currently, it is widely used as a power source for small-sized consumer electronics such as mobile phones, notebook computers, and various portable devices. Large non-aqueous electrolyte secondary batteries have also been put into practical use and are mounted, for example, in electric vehicles.

  A lithium secondary battery is one of the batteries using a non-aqueous electrolyte, and is used for the above-described applications. A lithium secondary battery has a battery container in which a metal battery can and a metal battery lid are caulked. The metal battery can has an opening on the negative electrode side (upper side) and is excellent in impact resistance. The battery can accommodates a group of electrodes obtained by winding or laminating positive and negative electrodes, and after a non-aqueous electrolyte is injected, the battery can be sealed by caulking a metal battery lid in the opening. For the metal battery can and the metal battery lid, a steel plate having a plating layer, a metal plate such as aluminum, an aluminum laminate film, or the like is used.

  When the metal (metal) constituting the metal battery can comes into contact with the non-aqueous electrolyte, metal ions of the metal may be eluted into the non-aqueous electrolyte. The eluted metal ions are deposited and grown on the negative electrode surface as a metal when the battery is charged and discharged. As a result, a minute short circuit between the positive and negative electrodes occurs through the separator separating the positive and negative electrodes, leading to a decrease in battery voltage.

  Corrosion on the outside of the battery can is caused by non-aqueous electrolyte adhering to the outside of the battery can in the manufacturing process or by adsorbing and absorbing halides such as sea salt particles in the atmosphere. Become.

  If a metal such as iron that elutes metal ions in the non-aqueous electrolyte is not used in the battery can, elution of metal ions in the metal can be prevented. However, in terms of cost, a battery can using a metal such as iron is preferable.

  By connecting the battery can to the negative electrode and using it in a negative polarity, when the lithium secondary battery is charged, the battery can is reduced by an electrical effect, so that metal ions can be hardly eluted. However, before charging the non-aqueous electrolyte secondary battery (from the time when the electrode group is accommodated in the battery can and the non-aqueous electrolyte is injected and then charged), the metal in the battery can elutes. In order to spread the non-aqueous electrolyte over the entire surface of the positive and negative electrodes and stabilize the initial charge and discharge characteristics, the non-aqueous electrolyte is injected depending on the area of the positive and negative electrodes and the injection method of the non-aqueous electrolyte. It is desirable that there are several days between charging and charging.

  In order to suppress elution of metal ions from the base metal of the battery can, there is a method of plating the battery can with a metal that is difficult to elute metal ions. For example, Patent Document 1 discloses a technique for forming a nickel plating layer containing a fine powder of fluororesin having excellent corrosion resistance on the surface of an iron battery can. As a plating method, barrel plating excellent in mass productivity (a method of plating while rotating a plating container containing a battery can) is effective.

  However, in ordinary barrel plating, a plating layer is hardly formed on the inner surface of the battery can. Moreover, even if a plating layer is formed, it becomes a thin layer. Therefore, micropores (micropores) of plating defects are easily formed. In addition, in the portion where the battery lid is crimped to the battery can, the battery can is deformed, so that the plating layer may break along with the deformation of the battery can. In particular, the thicker the plating layer, the higher the frequency. In the cracked part of the plating layer or the part where the micropores are formed, the base metal of the battery can comes into contact with the nonaqueous electrolytic solution, and metal ions are eluted from the base metal into the nonaqueous electrolytic solution.

  Therefore, in Patent Document 2, a lithium secondary battery formed by caulking a metal battery can and a metal battery lid, wherein the battery can is a negative electrode, the battery lid is a positive electrode, and the metal battery can It is disclosed that a plating layer is provided on the inner surface of the substrate, the thickness of the plating layer is 1 μm or more at the inner bottom surface, and 1 μm to 10 μm at the portion where the battery can and the battery lid are caulked.

JP 2002-231195 A JP 2007-87704 A

  When the battery can described in Patent Document 2 is caulked after deep drawing, the nickel-plated micropores are open. Therefore, iron components may elute from the bare metal on the outer surface. In addition, when a through hole is generated in the battery can due to the elution of iron from the metal part, the battery current may decrease because the electrolyte flows out to the outside.

  In view of the above, the present invention is to provide a secondary battery in which elution of metal ions in a metal battery can is further suppressed.

  A feature of the present invention that solves the above-described problems resides in that a steel plate provided by combining nickel plating and zinc plating is used for a battery container of a secondary battery. In particular, it is a secondary battery in which a non-aqueous electrolyte is filled in a battery container in which a metal battery can and a metal lid are caulked, and the battery can includes a nickel layer, a steel plate, zinc from the electrolyte side. It is comprised using the board | plate material which has a layer structure of the order of a layer and a nickel layer. Moreover, you may provide an aluminum layer and a zinc / aluminum mixed layer instead of a zinc layer. Furthermore, it is preferable that the battery lid has a similar structure. The present invention is particularly used for a lithium secondary battery using an electrolytic solution containing lithium.

  In the present invention, the plating layer of the metal battery can is multi-layered, so that it is possible to suppress the expansion of micropores that occurs when deep drawing or caulking. Further, the corrosion of the steel sheet caused by the intrusion of an external corrosive substance from a defective portion generated in the nickel plating layer is suppressed by using the zinc plating layer as a sacrificial anode. Furthermore, the corrosion product generated by the corrosion of the galvanized layer closes the defective portion of the nickel plating due to the increase in volume, and suppresses the progress of the corrosion. That is, by providing zinc plating, the effect of zinc as a sacrificial anode and the effect of repairing defects in nickel plating can be obtained.

  It is preferable that the battery can have a negative polarity and the battery lid has a positive polarity. Further, the battery can preferably has an outermost layer coated with a resin.

  It is desirable that the nickel plating has a thickness of 1 μm to 5 μm and the zinc plating has a thickness of 3 μm to 20 μm. The thickness of the steel plate is preferably 0.2 mm to 2 mm.

  The plated layer and the steel plate having these thicknesses can avoid the problem that a through hole is formed in the battery can and the battery current is reduced due to the non-aqueous electrolyte flowing out.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery which suppressed more the elution of the metal ion of a metal battery can can be provided. In addition, it is possible to prevent a short circuit due to metal elution and to prevent an electrolyte from flowing out, thereby reducing a decrease in battery current.

It is sectional drawing which shows the example of the cylindrical lithium secondary battery of this invention.

  Hereinafter, the lithium secondary battery to which the present invention is applied will be described in more detail with reference to the drawings.

  FIG. 1 shows an example of a cylindrical lithium secondary battery. The battery container is composed of a battery can and a battery lid. The battery can 4 is formed into a bottomed cylindrical shape by deep drawing a steel plate. The bottomed cylindrical battery can 4 is sealed with a metal upper lid (battery lid) 7 disposed on the upper side. The battery container has an electrode group 9 wound around the shaft core 10. The electrode group is formed by winding strip-shaped positive and negative electrodes in a spiral shape with a separator interposed therebetween.

  On the upper side of the electrode group 9, a positive electrode current collecting ring 5 for collecting a potential from the positive electrode is disposed on a substantially extension line of the shaft core 10. A disc-shaped upper lid 7 serving as a positive electrode external terminal is disposed on the positive electrode current collecting ring 5. The upper lid 7 is provided with a valve opening 8 that is cleaved when the internal pressure increases.

  On the other hand, a negative electrode current collecting ring 6 for collecting a potential from the negative electrode is disposed below the electrode group 9. The outer peripheral surface of the lower end portion of the shaft core 10 is fixed to the inner peripheral surface of the negative electrode current collecting ring 6.

  The metallic battery can and the metallic battery lid are caulked through an insulator. A constriction is formed in the upper part of the cylindrical can, and a donut-shaped insulator (resin) with an open center is placed, and a metal lid is placed thereon. After the insulator and the metal lid are stacked, the center of the lid is caulked so as to contact the lower positive electrode through the hole of the insulator. The battery can is insulated from the positive electrode and forms + and-electrodes like a dry battery.

  In order to prevent external mechanical damage and corrosion, the battery container is provided with a resin layer. An example of the resin layer is a polyethylene 50 μm film. The thickness of the resin film is preferably 10 to 100 μm in order to maintain mechanical strength and prevent permeation of corrosive substances such as moisture and halides.

  The thickness of the steel sheet is preferably 0.2 mm to 2 mm in order to withstand the mechanical strength of the cylindrical shape and the reduction in thickness against the general corrosion of about 5 years.

  The thickness of nickel plating is preferably 1 μm to 5 μm, and the thickness of zinc plating is preferably 3 μm to 20 μm. By using this level of plating, it is possible to suppress penetrating holes that exist as fine defects.

  In the present invention, it is preferable to apply nickel plating to the one-side galvanized steel sheet. However, as an alternative to zinc plating, aluminum plating, aluminum zinc mixed plating, zinc film, and aluminum foil can be used.

  The battery can is formed by deep drawing a steel plate. When a single-sided galvanized steel sheet is used, the steel sheet is processed so that the galvanized side is the outside of the battery can (the side not in contact with the electrolyte).

  The layer structure from the inner surface of the battery can 4 is shown enlarged in FIG. From the inside of the battery can, nickel plating 3, steel plate 1, zinc plating 2, and nickel plating 3 are laminated in this order. The plate material constituting the battery can is obtained by galvanizing one side of a steel plate and further nickel-plating both sides. A commercially available single-sided galvanized steel sheet may be nickel-plated and used.

  In nickel plating, a plating bath in which nickel sulfate, nickel chloride, boric acid or the like is dissolved in water is used, and in zinc plating, a plating bath in which zinc chloride, sodium hydroxide or the like is dissolved in water is used. When plating, an electrode having a shape similar to that of the battery can 4 is used. When galvanization is used, a plating layer is formed on one side of the steel plate (the side that becomes the outer surface of the battery can). A single-side galvanized steel sheet may be used instead of galvanizing. Next, nickel plating is performed, and plating layers are provided on both sides of the steel plate (the inner surface and the outer surface of the battery can 4). In nickel plating, the plating bath is agitated so that the concentration of the plating bath is constant even inside the battery can 4. The thickness of the plating layer can be adjusted by changing the current value of each electrode, and the thickness of the nickel plating is preferably 1 μm to 5 μm, and the thickness of the zinc plating is preferably 3 μm to 20 μm.

  The battery can is preferably molded after plating. However, if there is a plating defect, the defect is enlarged by molding. On the other hand, plating is preferably performed after molding, since there are few defective holes in plating, but there is a possibility that plating non-uniformity occurs in the plating solution after the plating step is performed with the non-aqueous electrolyte. Moreover, the trouble which prevents the leak of electrolyte solution arises.

After putting an electrode etc. in a battery can and injecting electrolyte solution, a battery can and a battery cover are crimped and sealed. As the electrolyte, various non-aqueous electrolytes can be used. In the examples described later, phosphorus hexafluoride is used as an electrolyte in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). lithium acid (LiPF ₆₎ was prepared by dissolving 1 mol / liter.

  In a conventional lithium secondary battery, a plating layer of nickel or the like is formed on the surface of the battery can in order to prevent metal ions such as iron ions from eluting from the steel plate used in the battery can into the non-aqueous electrolyte. On the outside, corrosion due to adhesion of electrolyte and sea salt particles in the battery manufacturing process may occur, and a nickel plating layer is formed. When the thickness of the plating layer is thinner than 1 μm, micropores (micropores) of plating defects are easily formed in the plating layer. In addition, when the thickness of the plating layer is larger than 10 μm, the plating layer can follow the deformation when the battery can is deformed when the battery can is stepped or when the battery lid is caulked to the battery can. In other words, cracks (including cracks and cracks) occur in the plating layer. Moreover, although there is an example which uses the inhibitor, even if it uses only an inhibitor, the corrosion inhibitory effect is not enough, and the corrosion check by a hand is needed.

  In the area where micropores and cracks occur, the base steel plate corrodes when it comes into contact with sea salt particles, moisture, and halogen-containing molecules, which are corrosive factors of the outside environment, and the steel plate is locally thinned, resulting in through holes. May occur and the electrolyte may flow out.

  Such corrosion is eliminated by providing a galvanized layer between the nickel plating and the steel plate. In particular, the corrosion of the steel sheet caused by the invasion of external corrosive substances from the defects generated in the nickel plating layer was suppressed by the galvanization layer serving as a sacrificial anode, and the galvanization layer was corroded. Corrosion products can also have a geometric shape that closes up defects in nickel plating due to their increased volume. That is, there is an effect of zinc as a sacrificial anode and a defect repair effect of nickel plating.

  The nickel layer may contain additives and other impurities as long as there is no problem in the effect of suppressing corrosion from the outside. Similarly, the galvanizing may be changed to a material such as aluminum which has a sacrificial anode effect on the nickel layer, and may contain other compounds as long as the effect is not affected.

  Next, examples of the manufactured lithium secondary battery will be described.

〔Example〕
<Creation of battery can>
In order to confirm the effect of the present invention, a battery can of an example in which a zinc plating layer and a nickel plating layer were provided on the outer surface of the battery can 4 was prepared. In Examples 1 to 9, the average plating thickness of each of the zinc plating layer and the nickel plating layer is changed and formed on the steel plate. The nickel plating thicknesses were 2 μm, 5 μm, and 8 μm, respectively, and the zinc plating thicknesses were 3 μm, 10 μm, and 20 μm. Table 1 shows the average plating thickness of each of the galvanized layer and the nickel plated layer in each example.

  Further, as Example 10, a battery can having a zinc plating layer containing 20% by mass of aluminum on the outer surface of the battery can 4 on a steel plate and a nickel plating layer of 5 μm provided thereon was prepared.

  The timing of plating in Examples 1 to 3 is after deep drawing. The timing of plating in Examples 4 to 10 is before deep drawing.

  As a comparative example, as shown in Table 1, a battery can of Comparative Example 1 formed without forming a nickel plating layer or a zinc plating layer, a comparative example in which only a 2 μm nickel plating layer was formed without providing a zinc plating layer 2 battery cans were made. The timing of nickel plating in Comparative Example 2 was after deep drawing.

  Using these battery cans, lithium batteries of Examples / Comparative Examples were prepared.

<Test and evaluation>
[Test 1: Confirmation of metal elution amount before charging 1 day]
Using the battery cans of Examples 5 to 7 and Comparative Examples 1 and 2, the amount of metal elution when left before charging was measured.

  A lithium battery was prepared by injecting a non-aqueous electrolyte into the battery can, and immersed in a 3.5 wt% aqueous sodium chloride solution at a temperature of 25 ° C. for 24 hours without charging. Thereafter, the iron ion concentration in the aqueous sodium chloride solution was measured. Table 1 shows the measurement results of the iron ion concentration.

In Examples 5 to 7 having a galvanized layer, the iron ion concentrations eluted from the steel sheet through plating were 0.002 g / cm ² , 0.001 g / cm ² and 0.3 g / cm ² , respectively. On the other hand, in the battery can of Comparative Example 1 where neither nickel plating nor zinc plating was applied, 5.3 g / cm ^{2 of} iron ions were eluted. Further, in Comparative Example 2 in which there was no zinc plating and only nickel plating, 2.2 g / cm ^{2 of} iron ions was eluted. In these comparative examples, the steel sheet was significantly corroded.

  Therefore, by providing the zinc plating layer 4 and the nickel plating layer 5, elution of iron ions is reduced, and corrosion of the steel sheet constituting the battery can can be suppressed.

[Test 2: Confirmation of metal elution amount before charging 7 days]
Similarly to Test 1, the batteries of Examples 4 to 8 were immersed in a 3.5 wt% aqueous sodium chloride solution for 168 hours (7 days). Thereafter, the holes generated in the plating due to the corrosive action were observed, and the number of holes seen with the naked eye was counted in the range of 1 cm ² . In any of the batteries of Examples 4 to 7, the number of holes was 3 or less. In Example 8, no holes were found at all.

  In plating, there are small holes that are invisible to the naked eye before the corrosion test, which expands due to corrosion and can be observed with the naked eye. When the Ni plating is thick, the number of through-holes decreases, so the number of holes seen in the appearance decreases. However, it can be seen that the base metal elution ions from fine defects are increasing. On the other hand, as the galvanizing is thicker, the base iron ions are not eluted. Zinc plating corrodes instead of the base metal (iron) and immediately forms a hydroxide immediately.

[Test 3: Confirmation of discoloration under high temperature and high humidity]
As in Test 1, the batteries of Examples 3 and 6 were left for 10 days in an atmosphere having an environmental temperature of 50 ° C. and a relative humidity of 90% or higher without being charged after the electrolyte solution was poured. Further, the batteries of Example 5 and Example 10 were similarly left for 7 days.

  Thereafter, the appearance of the battery can was visually examined. As a result, no change in appearance was observed in the batteries of Examples 3, 5, and 10. In the battery of Example 6, a change in appearance was observed near the deep surface of the battery can near the deep drawing. The discoloration is yellow brown and is due to the corrosion product of the base metal iron. The battery can of this example can suppress discoloration in appearance even when the battery is left in a hot and humid atmosphere.

  Thus, according to the battery can of the present embodiment, the occurrence of pitting corrosion due to adhesion of sea salt particles from the outside is suppressed, and thus durability is improved. As a result, due to the effect of suppressing the elution of metal ions from the metal, it can be suppressed that local corrosion occurs on the steel sheet and the battery current decreases. In addition, the multi-layered plating layer of the metal battery can suppresses the expansion of micropores that occur when deep drawing or caulking. In this way, it is possible to prevent a through hole from being formed in the battery can, and consequently, the non-aqueous electrolyte to flow out to the outside, and the battery current from being lowered.

  In addition, since the discoloration caused by the corrosion of the iron material due to the adhesion of the non-aqueous electrolyte is remarkably reduced, the yield is improved by 5% or more in production.

  In this example, the evaluation was performed by observing the outer surface. However, the corrosion of the inner surface causes a through hole in the battery can due to elution of metal ions, and the nonaqueous electrolyte flows out, leading to a decrease in battery current. According to the present invention, there is an effect of preventing corrosion on the inner surface side as well.

  Since the present invention provides a non-aqueous electrolyte secondary battery that can suppress a decrease in battery current due to elution of metal ions from a metal battery can, it contributes to the manufacture and sale of non-aqueous electrolyte secondary batteries. Has industrial applicability.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Zinc plating layer 3 Nickel plating layer 4 Battery can 5 Positive electrode current collection ring 6 Negative electrode current collection ring 7 Upper cover (metal battery cover)
8 Valve opening 9 Electrode group 10 Shaft core

Claims (6)

In a secondary battery using a non-aqueous electrolyte, a metal battery can and a metal battery lid are caulked, the battery container holding the electrolyte solution is used,
The battery can has a layer structure of a nickel layer, a steel plate, a zinc layer, and a nickel layer from the non-aqueous electrolyte side.   The secondary battery according to claim 1, further comprising an aluminum layer or a mixed layer of zinc and aluminum instead of the zinc layer.   The secondary battery according to claim 1, wherein the battery can has a resin film as an outermost layer.   The secondary battery according to claim 1, wherein the secondary battery is a lithium secondary battery using an electrolytic solution containing lithium.   2. The secondary battery according to claim 1, wherein the steel plate has a thickness of 0.2 mm to 2 mm, a nickel plating thickness of 1 μm to 5 μm, and a zinc plating thickness of 3 μm to 20 μm. Secondary battery.   The secondary battery according to claim 1, wherein the battery can and the battery lid have a structure that is caulked through an insulator.

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