JP2004103554A - Nonaqueous electrolyte liquid secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte liquid secondary battery equipped with a battery case hard to be corroded even at time of over discharge. <P>SOLUTION: The battery is provided with a battery case 11 functioning as a negative electrode terminal, and a positive electrode, a negative electrode, a separator and a nonaqueous electrolyte liquid housed in the battery case 11. The positive electrode and the negative electrode have an active material reversibly absorbing and releasing lithium. The battery case 11 includes a case 11a formed of a metal plate with iron as a main ingredient, and a metal layer 11b formed at least at a part of the inner face of the case 11a. The metal layer 11b contains a metal element M dissolved in the nonaqueous electrolyte liquid, of which the potential is lower than that of iron and higher than that of lithium. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery, and particularly to, for example, a lithium secondary battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the development of electronic devices, there has been a demand for the development of a secondary battery that is small and lightweight, has a high energy density, and can be repeatedly charged and discharged. As such batteries, nonaqueous electrolyte secondary batteries, particularly lithium secondary batteries using a positive electrode containing a composite oxide such as lithium cobalt oxide and a negative electrode containing a carbon material, are being actively researched. .
[0003]
[Problems to be solved by the invention]
In a non-aqueous electrolyte secondary battery, a battery case also serving as a negative electrode terminal is generally formed of a nickel-plated iron plate. This battery case is electrically connected to the negative electrode and has the same potential as the negative electrode. The potential of the negative electrode is a potential at which the carbon material intercalates / deintercalates lithium, and is a physical property of the carbon material, particularly the degree of development of the layered structure (interlayer distance, c-axis direction of the layer). It is about 1.5 V or less with respect to the dissolution potential of lithium, though it depends on the overlap and the spread of the layer in the a-axis direction). Since the potential of the negative electrode is lower than the corrosion potential of the metal used as the material of the battery case, the battery case is not corroded in a normal state.
[0004]
However, when the battery is over-discharged, the potential of the negative electrode rises to about 3.2 V or more with respect to the dissolution potential of lithium and becomes equal to the potential of the positive electrode. Since this potential is a potential at which iron dissolves, if the battery case is formed of a metal plate containing iron, the iron of the battery case is corroded. For example, when the battery case is formed of a nickel-plated iron plate, iron is more easily corroded than nickel, so that iron is corroded at a nickel-plated pinhole portion or a nickel-plated damaged portion. Such imperfect nickel plating is likely to occur in the constricted part of the case. If the battery case is severely corroded, a hole may be opened in the battery case and the non-aqueous electrolyte may leak.
[0005]
In order to solve such a problem, a battery case formed using austenitic stainless steel having high resistance to corrosion has been proposed (for example, see Patent Document 1). However, such a stainless steel has a complicated forming process and is expensive.
[0006]
In view of such circumstances, an object of the present invention is to provide a non-aqueous electrolyte secondary battery including a battery case that is hardly corroded even during overdischarge.
[0007]
[Patent Document 1]
JP-A-6-11849
[0008]
[Means for Solving the Problems]
To achieve the above object, a non-aqueous electrolyte secondary battery of the present invention includes a battery case that functions as a negative electrode terminal, and a non-aqueous electrolyte including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte contained in the battery case. An electrolyte secondary battery, wherein the positive electrode and the negative electrode each include an active material that reversibly stores and releases lithium, and the battery case is formed of a metal plate containing iron as a main component. And a metal layer formed on at least a part of the inner surface of the case, wherein the metal layer contains a metal element M whose potential dissolved in the non-aqueous electrolyte is lower than iron and higher than lithium. Features. In this specification, the main component means a component contained at a content of 95% by weight or more. Further, in this specification, the “iron plate” includes a general steel plate to which an element such as carbon is added in a small amount (for example, 5% by weight or less).
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
A non-aqueous electrolyte secondary battery of the present invention includes a battery case that functions as a negative electrode terminal, and a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte stored in the battery case. The positive electrode and the negative electrode each include an active material that reversibly stores and releases lithium. The battery case includes a case formed of a metal plate containing iron as a main component, and a metal layer formed on at least a part of an inner surface of the case, and the potential at which the metal layer dissolves in the nonaqueous electrolyte. Contains a metal element M lower than iron and higher than lithium. In this non-aqueous electrolyte secondary battery, even when the potential of the battery case rises above the potential at which iron dissolves in the overdischarge state, the metal element M is preferentially dissolved, so that iron can be prevented from dissolving. . Therefore, according to the present invention, it is possible to prevent the occurrence of liquid leakage due to corrosion of the battery case.
[0010]
The metal layer may be a layer formed by plating.
[0011]
Further, the battery case may include a nickel layer formed on an inner surface of the case, and the metal layer may be formed on the nickel layer.
[0012]
Further, the battery case may be formed of a clad material obtained by pressing the metal plate and the metal layer plate.
[0013]
The metal layer may be formed on at least a bottom corner of the inner surface of the case. Corrosion of the battery case is particularly likely to occur at the bent portion of the battery case. By forming the metal layer at the corner of the bottom of the case, corrosion at the bent portion of the bottom can be prevented.
[0014]
Further, the secondary battery of the present invention includes a sealing plate for sealing the battery case, wherein the battery case is formed with a constriction for fixing the sealing plate, and the metal layer is formed on the constricted portion. May be formed. The bent constricted portion is easily corroded, but by forming a metal layer on that portion, corrosion of the constricted portion can be prevented.
[0015]
The positive electrode, the negative electrode, and the separator may be wound in a coil shape to form an electrode group, and the metal layer may be formed near an end of the electrode group. Since the battery case is particularly susceptible to corrosion near the positive electrode, it is preferable to form a metal layer near the end of the electrode plate group.
[0016]
Further, it is preferable that the amount of electricity necessary for dissolving all of the metal elements M contained in the metal layer as metal ions is 4% or more of the battery capacity. According to this configuration, corrosion of the case formed of the metal plate can be particularly prevented. In this specification, the “battery capacity” means the battery capacity when the battery charged until the battery voltage reaches 4.2 V is discharged until the battery voltage reaches 3.0 V.
[0017]
Preferably, the metal element M is zinc. According to this configuration, it is possible to suppress deterioration of battery characteristics due to the metal element M.
[0018]
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. As an example of the non-aqueous electrolyte secondary battery of the present invention, a partially exploded side view of a non-aqueous electrolyte secondary battery 10 is shown in FIG.
[0019]
The non-aqueous electrolyte secondary battery 10 includes a battery case 11 functioning as a negative electrode terminal (hatching is omitted), a sealing body 12 for sealing the battery case 11, a positive electrode 13, a negative electrode 14, housed in the battery case 11, A separator 15 and a non-aqueous electrolyte (not shown) are provided. The positive electrode 13 and the negative electrode 14 each include an active material that reversibly stores and releases lithium. The positive electrode 13 and the negative electrode 14 are spirally wound with a separator 15 interposed therebetween to form an electrode plate group 16. Insulating plates 17 and 18 for preventing a short circuit are arranged on the upper and lower portions of the electrode plate group 16.
[0020]
In the non-aqueous electrolyte secondary battery of the present invention, members generally used for a lithium secondary battery can be used as members other than the battery case 11. Hereinafter, a specific description will be given.
[0021]
The sealing body 12 includes a positive electrode lid 12a and an insulating gasket 12b arranged around the positive electrode lid 12a. The sealing body 12 is supported and fixed by a constriction 11 c formed in the battery case 11.
[0022]
Positive electrode 13 includes a current collector and an active material layer formed on the current collector. As the current collector, for example, an aluminum foil can be used. As the active material included in the active material layer, a composite oxide containing lithium and a transition metal element can be used. For example, lithium cobaltate (LiCoO 2 ₂ ) Can be used. The positive electrode 13 is electrically connected to the positive electrode lid 12a by a positive electrode lead 19.
[0023]
The negative electrode 14 includes a current collector and an active material layer formed on the current collector. For the current collector, for example, a copper foil can be used. As the active material included in the active material layer, a carbon material that reversibly stores and releases lithium can be used. As the separator 15, for example, a microporous film made of a polyethylene resin can be used. The negative electrode 14 is electrically connected to the battery case 11 by a negative electrode lead 20. The non-aqueous electrolyte will be described later.
[0024]
Hereinafter, the battery case 11 will be described. FIG. 2 shows a cross-sectional view of the battery case 11. Battery case 11 includes a case 11a formed of a metal plate containing iron as a main component (having a content of 95% by mass or more), and a metal layer 11b formed on at least a part of the inner surface of case 11a. FIG. 2 shows a battery case 11 in which a metal layer 11b is formed on the entire inner surface of the case 11a.
[0025]
As the metal plate forming the case 11a, a plate made of iron or a general steel plate made of a metal obtained by adding an element such as carbon to iron can be used. The metal layer 11b contains a metal element M (which may be two or more elements) whose potential dissolved in the nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery 10 is lower than iron and higher than lithium. As the metal element M, zinc can be used. By using a zinc layer as the metal layer 11b, it is possible to suppress a decrease in battery characteristics caused by the metal layer 11b. Further, it is expected that elements such as magnesium, titanium, vanadium, and indium can be used as the metal element M. The amount of the metal element M contained in the metal layer 11b is such that the amount of electricity required to dissolve all of the metal element M is at least 4% of the battery capacity of the nonaqueous electrolyte secondary battery 10. Is preferred.
[0026]
Hereinafter, an example of measuring the dissolution potential of zinc and iron will be described. LiPF as non-aqueous electrolyte ₆ Was used at a concentration of 1.25M. As the solvent, a solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed at a volume ratio of 2: 3: 3 was used. When the dissolution potential of zinc in the non-aqueous electrolyte was measured, it was about +2.8 (V) with respect to the dissolution potential of lithium. On the other hand, when the dissolution potential of iron was measured, it was about +3.0 (V) with respect to the dissolution potential of lithium.
[0027]
The metal layer 11b can be formed by, for example, a plating method. The type of plating method is not particularly limited, and for example, an electrolytic plating method can be used. In this case, the case 11a may be formed by molding a metal plate on which the metal layer 11b is formed by a plating method. Further, the metal layer 11b may be formed on the case 11a by a plating method. Further, the battery case 11 may be formed by using a clad material obtained by pressing a plate serving as the metal layer 11b and a metal plate serving as the case 11a.
[0028]
Although FIG. 2 shows a case where the metal layer 11b is formed on the entire inner surface of the case 11a, the metal layer 11b may be formed on a part of the case 11a. The metal layer 11b is formed at least in a portion where the case 11a is particularly susceptible to corrosion. Of the case 11a, particularly easily corroded portions are portions where the case 11a is bent (for example, a constricted portion and a bottom portion) and portions located near both ends of the electrode plate group 16. Therefore, it is preferable that the metal layer 11b is formed at least in these portions.
[0029]
Further, as shown in FIG. 3, a battery case in which a nickel layer 21 is formed on the inner surface of a case 11a and a metal layer 11b is formed on the nickel layer 21 may be used. In this case, the case 11a including the nickel layer 21 can be formed using a nickel-plated metal plate. Alternatively, the nickel layer 21 may be formed by performing nickel plating on the case 11a formed of a metal plate. In this case, the nickel layer 21 can be formed using an electrolytic plating method or an electroless plating method. Also in the battery case of FIG. 3, the metal layer 11b (for example, a zinc layer) can be formed by the method described above, for example, the plating method. When the case 11a including the nickel layer 21 is used, a defect is easily generated in the nickel plating layer at the constriction 11c of the case 11a. Therefore, it is preferable to form the metal layer 11b at least on the constriction 11c.
[0030]
Hereinafter, an example of the method for manufacturing the nonaqueous electrolyte secondary battery of the present invention will be described. First, a carbon material (negative electrode active material) obtained by calcining an organic polymer compound (phenol resin, polyacrylonitrile, cellulose, etc.) and a rubber binder (for example, SBR) are added to a solvent and kneaded. A paste for a negative electrode is prepared. Then, this paste is applied to a current collector to form a negative electrode sheet, which is dried and then rolled. Thus, the negative electrode 14 having the active material layer formed on the surface is obtained.
[0031]
On the other hand, the positive electrode 13 has LiCoO as an active material. ₂ And using a fluorine-based binder (for example, PVDF) as the binder, in the same manner as the anode 14.
[0032]
Next, these are wound so that the separator 15 is disposed between the positive electrode 13 and the negative electrode 14, thereby producing a spiral electrode group 16. Next, the positive electrode 13 and the positive electrode lid 12 a are connected by the positive electrode lead 19, and the negative electrode 14 and the battery case 11 are connected by the negative electrode lead 20. At this time, insulating plates 17 and 18 are arranged at both ends of the electrode group 16. Next, a non-aqueous electrolyte is injected into the battery case 11. Next, the battery case 11 is sealed by the sealing body 12. Next, the battery is initially charged at a predetermined voltage. Thus, the non-aqueous electrolyte secondary battery of the present invention can be manufactured.
[0033]
The current collector of the negative electrode 14 may be a metal foil subjected to lath processing or a metal foil subjected to etching processing, in addition to the copper foil. The thickness of the current collector of the negative electrode 14 is preferably in the range of 10 to 50 μm.
[0034]
As the active material of the negative electrode, in addition to the above-described carbon material, a carbon material obtained by firing coke or pitch, artificial graphite, or natural graphite may be used. The shape of the negative electrode active material is preferably spherical, scaly, or massive. As the binder, at least one selected from the group consisting of a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (SBR), an acrylic polymer, and a vinyl polymer can be used. . As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, or polytetrafluoroethylene resin can be used. These binders are used after being dispersed in water or an organic solvent.
[0035]
The paste for the negative electrode may include a conductive aid and a thickener as necessary. As the conductive additive, at least one selected from the group consisting of acetylene black, graphite, and carbon fiber can be used. As the thickener, at least one selected from the group consisting of ethylene-vinyl alcohol copolymer, carboxymethyl cellulose, and methyl cellulose can be used.
[0036]
As a solvent for forming the paste for the negative electrode, a liquid capable of dispersing a binder can be used. For example, when using a binder dispersible in an organic solvent, the solvent may be N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethylsulfoxide, hexamethylsulfamide, tetramethyl At least one organic solvent selected from the group consisting of urea, acetone and methyl ethyl ketone can be used. On the other hand, when a binder dispersible in water is used, water can be used as a solvent.
[0037]
For kneading the paste for the negative electrode, for example, a planetary mixer, a homomixer, a pin mixer, a kneader, a homogenizer and the like can be used. Further, the paste may be kneaded by combining a plurality of them. At the time of kneading, a dispersant, a surfactant, a stabilizer and the like may be added to the paste.
[0038]
The paste can be applied to the negative electrode current collector using, for example, a slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure coater, or a dip coater. Drying after application is preferably performed in a state close to natural drying. However, productivity can be increased by heating and drying. Heating conditions are preferably in the range of 70 to 300 ° C. for 1 minute to 5 hours.
[0039]
The negative electrode sheet is rolled using a roll press until it reaches a target thickness. Rolling may be performed several times at a constant linear pressure, or may be performed several times while changing the linear pressure. In any case, the linear pressure is preferably in the range of 9800 to 19600 N / cm (1000 to 2000 kgf / cm).
[0040]
As the current collector of the positive electrode 13, a metal foil subjected to lath processing or a metal foil subjected to etching processing can be used in addition to the aluminum foil. The thickness of the current collector is preferably in the range of 10 to 60 μm.
[0041]
LiCoO is used as the positive electrode active material. ₂ Alternatively, a transition metal compound that accepts lithium ions as a guest can be used. Specifically, a composite oxide containing at least one element selected from the group consisting of cobalt, manganese, nickel, chromium, iron, and vanadium and lithium as the active material can be used. For example, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiCo _x Ni _(1-x) O ₂ (0 <x <1), LiCrO ₂ , ΑLiFeO ₂ And LiVO ₂ Can be used.
[0042]
Note that a conductive assistant, a thickener, a dispersant, a surfactant, a stabilizer, and the like may be added to the positive electrode paste as needed. As these, those similar to those described for the negative electrode 14 can be used. Further, the application of the paste for the positive electrode to the current collector, drying, and rolling can be performed in the same manner as the method for manufacturing the negative electrode 14.
[0043]
As the separator 15, a microporous film made of a polyolefin resin such as a polypropylene resin can be used in addition to a microporous film made of a polyethylene resin. The thickness of the separator 15 is preferably in the range of 15 to 30 μm.
[0044]
As the non-aqueous electrolyte, a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent can be used. Non-aqueous solvents include, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-dichloroethane, 1,3-dimethoxypropane, 4-methyl -2-pentanone, 1,4-dioxane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, sulfolane, 3-methyl-sulfolane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylformamide, dimethylsulfoxide, trimethyl phosphate, Or triethyl phosphate can be used. In addition, you may use these non-aqueous solvents in mixture of 2 or more types.
[0045]
As the lithium salt, a lithium salt having a high electron-withdrawing property is used. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ Can be used. You may use these electrolyte solutions in combination of 2 or more types. These electrolytes are preferably dissolved in the non-aqueous solvent so as to have a concentration in the range of 0.5 to 1.5 mol / liter.
[0046]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples. In the following examples, eighty kinds of batteries having different battery cases were produced, each of which was 50 pieces. Each battery had an ICR17500 size (17 mm in diameter and 50 mm in height) described in JIS C8711, and was manufactured so as to have a battery capacity of 800 mAh. Then, it was tested whether or not liquid leakage occurred at the time of overdischarge for the produced battery.
[0047]
The test was performed as follows. After finishing charging and discharging the assembled battery, it was aged at a temperature of 45 ° C. for 2 weeks and further left at a room temperature of 20 ° C. for 1 week. After that, constant current charging of 800 mA (1 CmA) was performed until the battery voltage reached 4.2 V, and then constant current discharging of 800 mA (1 CmA) was performed until the battery voltage reached 3.0 V. Thereafter, the battery was left in an environment at a temperature of 60 ° C. for 30 days in a state where a constant resistance of 1 kΩ was connected to the battery, so that the battery was overdischarged. Thereafter, the number of leaked batteries was counted. Hereinafter, a method for manufacturing each battery will be described.
[0048]
(Battery A)
A mixture of 100 parts by mass of flaky graphite as a negative electrode active material, 4 parts by mass of a styrene butadiene rubber (binder), and an aqueous solution of 0.8 parts by mass of carboxymethyl cellulose (thickener) A paste was prepared by kneading with a planetary mixer. Next, this paste was applied to a strip-shaped copper foil (thickness: 14 μm) using a slit die coater and dried to prepare a sheet (thickness: 300 μm) having an active material layer formed on the surface. Next, this sheet was rolled three times at a linear pressure of 1080 N / cm (110 kgf / cm) using a roll press to obtain a negative electrode plate having a thickness of 196 μm.
[0049]
An aqueous dispersion of 100 parts by mass of lithium cobalt oxide as a positive electrode active material, 3 parts by mass of acetylene black carbon powder (conductive agent), 4 parts by mass of polytetrafluoroethylene resin (binder), and carboxymethyl cellulose A mixture with 0.8 parts by mass of an aqueous solution was kneaded with a planetary mixer to prepare a paste. Next, this paste was applied to a strip-shaped aluminum foil (thickness: 20 μm) using a slit die coater and dried to prepare a sheet (290 μm thick) having an active material layer formed on the surface.
[0050]
Next, this sheet was rolled three times using a roll press at a linear pressure of 9800 N / cm (1000 kgf / cm) to obtain a positive electrode plate having a thickness of 180 μm. Subsequently, the positive electrode lead 19 was spot-welded to a portion of the positive electrode plate where the current collector (aluminum foil) was exposed, and then dried at 250 ° C. for 10 hours. Next, a polypropylene separator (thickness: 20 μm) was sandwiched between the positive electrode 13 and the negative electrode 14 and spirally wound to form an electrode group. This electrode plate group was housed in a battery case in which an insulating plate was arranged at the bottom. In the battery A, an iron plate case having a galvanized layer formed on the inner surface was used as the battery case. This battery case was manufactured by molding an iron plate having zinc plated on one side into the shape of the case.
[0051]
Next, the positive electrode lead was connected to the positive electrode cover, and the negative electrode lead was connected to the bottom of the battery case. Then, an insulating plate was arranged above the electrode plate group. Subsequently, a predetermined amount of electrolyte was injected into the battery case. As the electrolyte, a solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate is added to lithium hexafluorophosphate (LiPF) as the electrolyte. ₆ ) Was dissolved at a rate of 1.25 mol / liter. Next, the battery case was sealed using a positive electrode lid and a gasket made of polypropylene resin. Next, the battery was initially charged at a predetermined voltage to prepare a battery A having an ICR17500 size and a battery capacity of 800 mAh described in JIS C8711. The 50 batteries A were placed in an overdischarged state under the above-described conditions, and whether or not liquid leakage occurred was observed.
[0052]
In the battery A, the amount of zinc in the galvanized layer formed on the inner surface of the battery case was about 39 mg. The amount of electricity required to electrochemically dissolve all of the zinc in the zinc layer as zinc ions was about 32 mAh, an amount corresponding to about 4% of the battery capacity. The number of batteries A that leaked due to overdischarge was 0 out of 50, and good results were obtained.
[0053]
(Battery B)
Battery B was produced in the same manner as Battery A except for the battery case. As the battery case of the battery B, a battery case formed using a nickel-plated iron plate was used. 9 out of 50 batteries B leaked due to overdischarge.
[0054]
(Battery C)
Battery C was fabricated in the same manner as Battery A, except that the amount of zinc in the zinc layer formed on the inner surface of the battery case was about 20 mg. The amount of electricity required to electrochemically dissolve all of the zinc in the zinc layer as zinc ions was about 16 mAh, an amount corresponding to about 2% of the battery capacity. The number of batteries C that leaked due to overdischarge was 3 out of 50.
[0055]
(Battery D)
Battery D was produced in the same manner as Battery A except for the battery case. As a battery case of the battery D, a case in which a zinc layer was formed by plating on the inner surface of a case formed of a nickel-plated iron plate was used. The amount of zinc in this zinc layer was about 39 mg. The amount of electricity required to electrochemically dissolve all of the zinc in the zinc layer as zinc ions was about 32 mAh, an amount corresponding to about 4% of the battery capacity. The number of batteries D that leaked due to overdischarge was 0 out of 50, and good results were obtained.
[0056]
(Battery E)
Battery E was produced in the same manner as Battery A except for the battery case. As the battery case of the battery E, a case was used in which a zinc layer was formed by plating around an upper constricted portion on the inner surface of the case formed of a nickel-plated iron plate and its periphery. The zinc content of this zinc layer was about 42 mg. The amount of electricity required to electrochemically dissolve all of the zinc in the zinc layer as zinc ions was about 34 mAh, an amount corresponding to about 4% of the battery capacity. The number of batteries E that leaked due to overdischarge was 0 out of 50, and good results were obtained.
[0057]
(Battery F)
Battery F was fabricated in the same manner as Battery A except for the battery case. As the battery case of the battery F, a case was used in which a zinc layer was formed by plating on the inner bottom surface and the periphery of the case formed of a nickel-plated iron plate. The zinc content of this zinc layer was about 40 mg. The amount of electricity required for electrochemically dissolving all of the zinc in the zinc layer as zinc ions was about 33 mAh, which was about 4% of the battery capacity. The number of batteries F that leaked due to overdischarge was 0 out of 50, and good results were obtained.
[0058]
(Battery G)
Battery G was produced in the same manner as Battery A except for the battery case. As the battery case of the battery G, a case was used in which a zinc layer was formed by plating on the upper constricted portion and its periphery and on the bottom and its periphery of the inner surface of the case formed of a nickel-plated iron plate. The total amount of zinc in the two zinc layers was about 40 mg. The amount of electricity required for electrochemically dissolving all of the zinc in the zinc layer as zinc ions was about 33 mAh, which was about 4% of the battery capacity. The number of batteries G that leaked due to overdischarge was 0 out of 50, and good results were obtained.
[0059]
(Battery H)
Battery H was fabricated in the same manner as Battery A except for the battery case. As a battery case of the battery H, a case formed by molding an iron plate (cladding material) obtained by pressing a zinc plate was used. A battery case was produced by molding a clad material such that the zinc plate was inside the case. The amount of zinc in the zinc layer (zinc plate) inside the battery case was about 50 mg. The amount of electricity required to electrochemically dissolve all of the zinc in the zinc layer as zinc ions was about 41 mAh, an amount corresponding to about 5% of the battery capacity. The number of batteries H that leaked due to overdischarge was 0 out of 50, and good results were obtained.
[0060]
As is clear from the above results, the batteries A and C to H in each of which the zinc layer was formed on the inner surface of the battery case had a lower rate of liquid leakage than the battery B. By setting the amount of zinc in the zinc layer on the inner surface of the battery case such that the amount of electricity required to dissolve the zinc into zinc ions is 4% or more of the battery capacity, the rate of occurrence of liquid leakage was particularly reduced. .
[0061]
Although FIG. 1 illustrates a cylindrical battery, the present invention is not limited to a cylindrical battery, and can be applied to batteries having other shapes such as a square battery.
[0062]
【The invention's effect】
As described above, in the nonaqueous electrolyte secondary battery of the present invention, the metal layer containing the metal element M having a lower dissolution potential than iron is formed on the inner surface of the battery case. Can be prevented from being corroded. Therefore, according to the present invention, a non-aqueous electrolyte secondary battery with a low possibility of liquid leakage even during overdischarge can be obtained.
[Brief description of the drawings]
FIG. 1 is a partially exploded side view showing an example of a nonaqueous electrolyte secondary battery of the present invention.
FIG. 2 is a cross-sectional view showing an example of a battery case used for the non-aqueous electrolyte secondary battery of the present invention.
FIG. 3 is a sectional view showing another example of the battery case used for the non-aqueous electrolyte secondary battery of the present invention.
[Explanation of symbols]
10 Non-aqueous electrolyte secondary battery
11 Battery case
11a case
11b metal layer
11c Constriction
12 Sealing body
12a Positive electrode lid
12b insulating gasket
13 Positive electrode
14 Negative electrode
15 Separator
16 Electrode group
17, 18 Insulating board
19 Positive electrode lead
20 Negative electrode lead
21 Nickel layer

Claims (9)

A battery case functioning as a negative electrode terminal, a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte contained in the battery case,
The positive electrode and the negative electrode each include an active material that reversibly stores and releases lithium,
The battery case includes a case formed of a metal plate containing iron as a main component, and a metal layer formed on at least a part of an inner surface of the case,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal layer includes a metal element M having a lower potential than the iron to dissolve in the non-aqueous electrolyte. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal layer is a layer formed by plating. The non-aqueous electrolyte secondary battery according to claim 1, wherein the battery case includes a nickel layer formed on an inner surface of the case, and the metal layer is formed on the nickel layer. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the battery case is formed of a clad material obtained by pressing a plate to be the metal layer and the metal plate. 3. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal layer is formed on at least a bottom corner of the inner surface of the case. 3. 2. The battery case according to claim 1, further comprising a sealing plate that seals the battery case, wherein the battery case is formed with a constriction for fixing the sealing plate, and the constriction is formed with the metal layer. 3. Non-aqueous electrolyte secondary battery. The non-electrode according to claim 1, wherein the positive electrode, the negative electrode, and the separator are spirally wound to form an electrode group, and the metal layer is formed near an end of the electrode group. Water electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of electricity required to dissolve all of the metal elements M contained in the metal layer as metal ions is 4% or more of the battery capacity. 3. 9. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal element M is zinc.

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