JP2002231195A - Non-aqueous electrolyte secondary battery and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion proof non-aqueous electrolyte secondary battery by coating a metallic armor can with a composite plating material whose corrosion proof characteristic does not easily deteriorate even when it is stored for a long period. SOLUTION: This non-aqueous electrolyte secondary battery has composite plating layers 10a, 10b composed of nickel metal and fluororesin fine powdered particles on a surface of the metallic armor can 10. As the fluororesin fine powdered particles having superior corrosion proof characteristic is uniformly attached to the surface of the metallic armor can 10, with nickel metal by forming the composite plating layers 10a, 10b composed of nickel metal and fluororesin fine powdered particles on the surface of the metallic armor can 10, the corrosion proof characteristic of the metallic armor can 10 can be improved. Whereby the corrosion of the metallic armor can 10 can be prevented even in the rise of potential of the metallic armor can 10 by the rise of potential of a negative electrode in an over-discharge state of the non-aqueous electrolyte secondary battery, and the long-term storage stability can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode group in which a negative electrode capable of occluding and releasing lithium ions and a positive electrode capable of occluding and releasing lithium ions are opposed to each other via a separator, and an organic solvent. The present invention relates to a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte in which a lithium salt is dissolved as a solute, and in particular, an improvement in a metal outer can containing an electrode group and a non-aqueous electrolyte and use of the metal outer can The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, lithium-cobalt composite oxides (LiCo) have been used as batteries used in portable electronic and communication devices such as small video cameras, mobile phones, and notebook computers.
O ₂ ), lithium-nickel composite oxide (LiNi
O ₂ ), lithium-manganese composite oxide (LiMn)
A lithium-containing transition metal composite oxide or manganese dioxide (MnO ₂ ) capable of occluding and releasing lithium ions such as ₂ O ₄ ) is used as a positive electrode active material, and lithium metal, a lithium alloy or lithium ions are inserted and released. Attention has been paid to lithium secondary batteries typified by lithium ion batteries using a carbon material or the like as a negative electrode active material, and lithium secondary batteries using a carbon material as a negative electrode active material have come into practical use.

In this type of lithium secondary battery, a negative electrode provided with the above-described negative electrode active material and a positive electrode provided with the above-described positive electrode active material are laminated with a separator interposed therebetween to form an electrode group. The electrode group and the nonaqueous electrolyte in which a lithium salt is dissolved as a solute in an organic solvent are housed in a metal outer can (battery container) and sealed. As a metal outer can used for this kind of lithium secondary battery, an iron outer can that is inexpensive and easy to manufacture is used.

[0004]

However, when an iron outer can is used, a corrosion current flows through the iron outer can as the battery voltage decreases due to the progress of overdischarge, and the iron outer can becomes corroded. The problem arises. Here, the reason why the iron outer can corrodes is considered as follows.
That is, assuming that the battery voltage (difference between the potential of the positive electrode and the potential of the negative electrode) in the discharge state in normal use is about 3.0 V, the positive electrode based on the potential of lithium metal in the non-aqueous electrolyte is referred to. The potential is 3.5 V to 3.7 V, and the negative electrode potential is 0.5 V to
It is about 0.7V.

By the way, when the battery in such a state is further discharged to an overdischarged state, FIG. 4 (FIG. 4 is based on the lithium metal of the negative electrode and the positive electrode when the nonaqueous electrolyte battery is overdischarged). FIG. 3 is a diagram schematically showing the state of the change of the potential and the battery voltage.)
Battery voltage drops further. More specifically, the potential of the positive electrode does not fluctuate so much even in the overdischarge state, but the potential of the negative electrode gradually increases, and eventually the potential based on the lithium metal of the negative electrode exceeds 3 V. When the potential of the negative electrode rises so as to exceed 3 V, the iron outer can reaches a corrosion potential, and iron constituting the outer can elutes into the electrolytic solution to cause a corrosion current to flow. The outer can will corrode.

[0006] Therefore, an outer can having an improved corrosion resistance has been used by increasing the corrosion potential by applying nickel plating to the surface of the outer can made of iron. However, even if nickel plating is performed on the surface of the iron outer can, the nickel plating layer (film) formed on the surface of the outer can is not perfect. This is because there is a defect or the like in the nickel plating film and a crack or the like is generated in the plating of the processed portion because a process such as grooving for caulking the sealing body in the outer can is performed at the time of assembling the battery. Therefore, in a nickel-plated iron outer can, a corrosion current flows through these defects and cracks and the like, and the corrosion progresses, so that it is enough to withstand long-term storage. It was not something. Therefore, the present invention has been made in order to solve the above problems, coating the surface of a metal outer can with a composite plating layer that does not easily deteriorate in corrosion resistance even when stored for a long time, has excellent corrosion resistance, It is an object of the present invention to provide a non-aqueous electrolyte battery having excellent storage characteristics.

[0007]

Means for Solving the Problems and Actions / Effects To achieve the above object, a non-aqueous electrolyte secondary battery of the present invention comprises nickel metal and fluororesin fine powder particles on the surface of a metal outer can. A composite plating layer is provided. As described above, when the composite plating layer composed of nickel metal and fluororesin fine powder particles is provided on the surface of the metal outer can, the fluororesin fine powder having excellent corrosion resistance is uniformly formed on the surface of the metal outer can together with the nickel metal. , The corrosion resistance of the metal outer can is improved. Thereby, even if such a nonaqueous electrolyte secondary battery is in an overdischarged state, the metal outer can electrically connected to the negative electrode in the battery can be prevented from reaching the corrosion potential,
The corrosion current can be prevented from flowing through the metal outer can, and the long-term storage characteristics of the nonaqueous electrolyte secondary battery can be improved. It is desirable to use polyvinylidene fluoride (PVdF) on which a favorable plating layer is formed as the fluororesin, and it is preferable that the metal outer can be an iron outer can that is inexpensive and easy to manufacture.

[0008] In this case, if the metal outer can is immersed in a plating bath in which fine particles of fluororesin are dissolved in an aqueous solution in which nickel metal is dissolved and electrolytic plating is performed, the surface of the metal outer can can be treated. A composite plating layer composed of nickel metal and fluororesin fine powder particles can be easily formed. However, if a composite plating layer composed of nickel metal and fine particles of fluororesin is formed on the inner surface of the bottom of the metal outer can, the composite plating layer is slightly inferior in conductivity. When welding the bottom of the inner surface and the current collecting tab extending from the negative electrode of the electrode group, welding failure may occur.

Therefore, a welding step of previously welding a metal piece to the inner surface of the bottom of the metal outer can and a step of applying an inner protective film to the surface of the metal piece welded to the inner surface of the bottom are performed in advance. Are provided before the plating step. Thereby, after the protective film adhered to the surface of the metal piece is peeled off, if the current collecting tab extending from the negative electrode of the electrode group is welded to the metal piece, the conductivity of the metal piece is good. Therefore, it is possible to prevent welding defects from occurring. In addition, before the plating step, if an external protective film applying step of applying a protective film to the bottom outer surface of the metal outer can in advance is provided, the outer portion of the bottom of the metal outer can which will later become a negative terminal is provided. Since a composite plating layer composed of nickel metal and fluororesin fine powder particles is not formed on the surface, the bottom outer surface of the metal outer can becomes a negative electrode terminal having excellent conductivity. Further, it is desirable to separately apply nickel plating only to a portion that is not composite-plated in order to prevent rust, since the corrosion resistance of the portion is improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described below. 1. Preparation of Sample Piece (1) Example 1 After preparing an electrolytic solution (plating bath) in which fine particles of polyvinylidene fluoride (PVdF) having a particle size of about 5 μm were dispersed in an aqueous solution of nickel sulfamate, the electrolytic solution was prepared. It was filled in the plating tank. Then, an iron piece (having a thickness of 0.25 mm, a width of 8 mm, and a length of 10 mm) was immersed in the electrolytic solution, and a plating current having a cathode current density of 10 A / dm ² was passed through the iron piece. A composite plating layer made of nickel metal and PVdF fine powder particles was formed on the surface of the iron piece to obtain a sample piece α of Example 1.

(2) Example 2 After preparing an electrolytic solution (plating bath) in which fine particles of polytetrafluoroethylene (PTFE) having a particle size of about 5 μm are dispersed in an aqueous solution of nickel sulfamate, the electrolytic solution is plated. The tank was filled. Then, an iron piece (having a thickness of 0.25 mm, a width of 8 mm, and a length of 10 mm) was immersed in the electrolytic solution, and a plating current having a cathode current density of 10 A / dm ² was passed through the iron piece. A composite plating layer composed of nickel metal and PTFE fine powder particles was formed on the surface of the iron piece to obtain a sample piece β of Example 2.

(3) Comparative Example 1 After an electrolytic solution (plating bath) composed of an aqueous solution of nickel sulfamate was filled in a plating tank, iron pieces (thickness 0.25 mm, width 8 mm, long Saga 10m
m), and a plating current having a cathode current density of 10 A / dm ² was passed through the iron piece to form a nickel metal layer on the surface of the iron piece.

(4) Comparative Example 2 An iron piece (having a thickness of 0.25 mm, a width of 8 mm, and a length of 1
0 mm) was prepared, and a polypropylene sheet was adhered to both surfaces of the iron piece to obtain a sample piece δ of Comparative Example 2.

(5) Comparative Example 3 Iron piece (thickness 0.25 mm, width 8 mm, length 1
0 mm) is prepared, an N-methyl-2-pyrrolidone (NMP) solution in which polyvinylidene fluoride (PVdF) is dissolved is applied to both surfaces of the iron piece, and then dried to evaporate NMP. A PVdF layer was formed on the surface of the iron piece to obtain a sample piece ε of Comparative Example 3.

2. Fabrication of Triode Electrochemical Cell Next, as shown in FIG. 1 (FIG. 1 is a diagram schematically showing a schematic configuration of the trielectrode electrochemical cell), these sample pieces α, β, Using γ, δ, ε as the working electrode 1 and using a lithium metal plate as the counter electrode 2 and the reference electrode 3 of the working electrode 1, the three-electrode electrochemical cells Α, Β, Γ,
Δ and Ε were prepared respectively. That is, a solution prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) mixed at a volume ratio of 1: 1 is used as an organic solvent. These organic electrolytes, the working electrode 1, the counter electrode 2 and the reference electrode 3 were housed in a glass cell container 7 to form a three-electrode electrochemical cell Α, Β, Γ,
Δ and Ε were prepared respectively. Then, each working electrode 1, counter electrode 2 and reference electrode 3 were connected to a power supply 8 with an ammeter via a working electrode lead 4, a counter electrode lead 5 and a reference electrode lead 6, respectively.

3. Measurement of Corrosion Current Next, at room temperature (about 25 ° C.), each working electrode 1 of each of the three-electrode electrochemical cells Α, Β, Γ, Δ, Ε prepared as described above.
After holding for 10 minutes while applying a potential of 3.2 V with respect to the lithium metal of each reference electrode 3, the current (μA) flowing through the ammeter was measured, and the total amount of electricity flowing through each working electrode 1 was measured. (ΜC) yielded the results shown in Table 1 below. Applying a potential of 3.2 V to each working electrode 1 based on the lithium metal of each reference electrode 3 means that the negative electrode potential of the overdischarged battery of FIG. Therefore, it can be said that the overdischarge state of the nonaqueous electrolyte secondary battery is reproduced.

[0017]

[Table 1]

As is evident from the results shown in Table 1, the current value and the total amount of electricity of the cell 用 い using the sample α (formed with a composite plating layer composed of nickel metal and PVdF fine powder particles) are remarkably large. It can be seen that the current value and the total amount of electricity of the cell 用 い using the specimen β (the composite plating layer formed of nickel metal and PTFE fine powder particles) were small. On the other hand, a cell を using a sample ε (with a PVdF layer formed), a cell 試 料 using a sample γ (with a nickel metal layer formed), and a sample δ
It can be seen that the current value and the total amount of electricity increase in the order of the cells Δ using (adhered polypropylene sheet).

This is because, in the sample piece δ in which the polypropylene sheet is adhered to the iron piece, the entire surface of the iron piece cannot be completely covered with the polypropylene sheet, and the portion not covered with the polypropylene sheet or the iron piece and the polypropylene sheet This is because current (corrosion current) flows through the gap. Further, in the sample piece γ in which the nickel metal layer was formed on the iron piece, the nickel metal layer formed by plating was not perfect, and there were defects and the like, and current (corrosion current) flowed through the defects and the like. It is. Furthermore, in the sample ε in which the PVdF layer was formed on the iron piece, the NMP solution in which PVdF was dissolved could not be uniformly applied to the iron piece, and a current (corrosion current) flowed through the non-uniform portion.

On the other hand, in the sample piece β on which the composite plating layer composed of nickel metal and PTFE fine powder particles was formed, the PTFE fine powder particles adhering to the nickel metal uniformly adhered to the iron pieces, and the composite plating layer was uniformly formed. It is considered that the current (corrosion current) flowing through the specimen β was reduced due to the formation. Furthermore, in the sample piece α on which the composite plating layer composed of nickel metal and PVdF fine powder particles was formed, the PVdF fine powder particles adhered to the nickel metal uniformly adhered to the iron piece, and the composite plating layer was formed uniformly. At the same time, although the reason is unknown, it is considered that the current (corrosion current) flowing through the sample α was further reduced because a plating layer better than PTFE was formed.

Next, in order to examine the difference in corrosion resistance when a lithium secondary battery was formed, a lithium secondary battery was manufactured in the following procedure, and the difference in corrosion resistance was examined.

4. Production of Metallic Outer Can (1) Example 1 Using an iron plate having a predetermined thickness, this iron plate was subjected to plastic working (press processing) to obtain a cylindrical outer can 10 having a predetermined size as shown in FIG. Is prepared, a nickel plate having a predetermined shape (having a thickness of 0.1 mm) is formed at the center of the inner surface of the bottom of the cylindrical outer can 10.
17 mm in length and 5 mm in length and width, respectively, were resistance welded. Thereafter, a polypropylene protective film 18 was adhered to the surface of the nickel plate 17 and a polypropylene circular protective film 19 was adhered to the outer surface of the bottom of the cylindrical outer can 10.

Thereafter, polyvinylidene fluoride (PVd) having a particle size of about 5 μm is added to an aqueous nickel sulfamate solution.
F) The cylindrical outer can 10 produced as described above was immersed in a plating tank filled with an electrolytic solution (plating bath) in which fine powder particles were dispersed. Then, a plating current having a cathode current density of 10 A / dm ² was passed through the cylindrical outer can 10,
A composite plating layer 10a made of nickel metal and PVdF fine powder particles was formed on the entire surface of the cylindrical outer can 10. Thereafter, the protective film 18 and the circular protective film 19 were peeled off, and the outer can a of Example 1 was manufactured.

(2) Embodiment 2 Similarly, as shown in FIG. 2 (a), a cylindrical outer can 10 was prepared, and a nickel plate (thickness) was formed at the center of the inner surface of the bottom of the cylindrical outer can 10. Is 0.1 mm, and the vertical and horizontal lengths are each 5 mm.) 17 After welding, a protective film 18 made of polypropylene is stuck on the surface of the nickel plate 17 and the bottom of the cylindrical outer can 10 is A circular protective film 19 made of polypropylene was adhered to the outer surface. Next, the cylindrical outer can 10 is placed in a plating tank filled with an electrolytic solution (plating bath) in which fine particles of polytetrafluoroethylene (PTFE) having a particle size of about 5 μm are dispersed in an aqueous nickel sulfamate solution.
Was immersed. Then, 10 A /
By passing a plating current having a cathode current density of dm ^2, a composite plating layer 10 b composed of nickel metal and PTFE fine powder particles was formed on the entire surface of the cylindrical outer can 10. Next, the protective film 18 and the circular protective film 19 were peeled off, and an outer can b of Example 2 was produced.

(3) Comparative Example 1 Using an iron plate having a predetermined thickness, this iron plate was subjected to plastic working (press processing) to produce a cylindrical outer can 10 having predetermined dimensions as shown in FIG. 2B. Thereafter, a nickel plate of a predetermined shape (having a thickness of 0.1 mm) is formed at the center of the inner surface of the bottom of the cylindrical outer can 10.
17 mm in length and 5 mm in length and width, respectively, were resistance welded. Next, the cylindrical outer can 10 is immersed in a plating tank filled with an electrolytic solution composed of an aqueous solution of nickel sulfamate, and the cylindrical outer can 10 is filled with 10 A / d.
A plating current having a cathode current density of m ² is passed to form a nickel metal layer 10 c on the surface of the cylindrical outer can 10.
An outer can c of Comparative Example 1 was produced.

(4) Comparative Example 2 Using an iron plate having a predetermined thickness, this iron plate was subjected to plastic working (press processing) to produce a cylindrical outer can 10 having predetermined dimensions as shown in FIG. 2 (c). Thereafter, a nickel plate of a predetermined shape (having a thickness of 0.1 mm) is formed at the center of the inner surface of the bottom of the cylindrical outer can 10.
17 mm in length and 5 mm in length and width, respectively, were resistance welded. Next, a polypropylene sheet 10d was bonded to the entire inner surface of the cylindrical outer can 10 except for the nickel plate 17 welded to the center of the inner surface of the bottom of the can to produce an outer can d of Comparative Example 2.

(5) Comparative Example 3 Using an iron plate having a predetermined thickness, this iron plate was subjected to plastic working (press processing) to produce a cylindrical outer can 10 having predetermined dimensions as shown in FIG. 2 (c). Thereafter, a nickel plate of a predetermined shape (having a thickness of 0.1 mm) is formed at the center of the inner surface of the bottom of the cylindrical outer can 10.
17 mm in length and 5 mm in length and width, respectively, were resistance welded. Next, an N-methyl-2-pyrrolidone (NMP) solution in which polyvinylidene fluoride (PVdF) is dissolved on the entire inner surface of the cylindrical outer can 10 except for the nickel plate 17 welded to the center of the inner surface of the can bottom. Was applied. Next, the applied container was dried to evaporate the NMP to form a PVdF layer 10e on the inner surface of the cylindrical outer can 10, thereby producing an outer can e of Comparative Example 3.

5. Preparation of Nonaqueous Electrolyte Secondary Battery (1) Preparation of Positive Electrode A positive electrode active material made of LiCoO ₂ , a carbon-based conductive agent such as acetylene black and graphite, a binder made of polyvinylidene fluoride (PVdF), and the like To N-
Slurries were prepared by mixing those dissolved in an organic solvent such as methyl-2-pyrrolidone (NMP). The slurry was uniformly applied to both surfaces of a positive electrode current collector (for example, an aluminum foil or an aluminum alloy foil) using a die coater or a doctor blade to form a positive electrode plate coated with an active material layer. Thereafter, the slurry is passed through a dryer, and the organic solvent (NM
P) was removed. After drying, the dried positive electrode plate was rolled to a predetermined thickness by a roll press machine, and then cut to a predetermined size to produce a belt-shaped positive electrode 11.

(2) Preparation of Negative Electrode On the other hand, a negative electrode active material made of natural graphite (d = 3.36 °) and a binder made of polyvinylidene fluoride (PVdF) are mixed with N-methyl-2-pyrrolidone ( NMP) was dissolved in an organic solvent or the like to prepare a slurry. These slurries are applied to a negative electrode current collector (for example, copper foil) using a die coater or a doctor blade, dried, rolled to a predetermined thickness, and then cut to a predetermined size to produce a band-shaped negative electrode 12. did.

(3) Fabrication of Non-Aqueous Electrolyte Secondary Battery Next, as shown in FIG. 3, the band-shaped positive electrode 11 and the band-shaped negative electrode 12 prepared as described above were reacted with an organic solvent with low reactivity. They were superposed with a separator 13 made of a microporous polyolefin resin therebetween. Thereafter, it was wound by a winder (not shown), and the outermost periphery was taped to form an electrode group. Next, after the insulating plates 14 were arranged above and below the electrode group, the electrode group was inserted through the opening of each of the outer cans 10 (a, b, c, d, and e) manufactured as described above. Next, a negative electrode current collecting tab 12a extending from the negative electrode 12 of the electrode group was resistance-welded to a nickel plate 17 that was resistance-welded to the inner bottom of each outer can 10.

Next, a groove was formed on the upper portion of each outer can 10 to form an annular groove 10x, and an insulating gasket 16 was mounted on the annular groove 10x. afterwards,
The positive electrode current collecting tab 11a extending from the positive electrode 11 of the electrode group was welded to the bottom of the bottom plate of the sealing body 15. Then, a nonaqueous electrolyte (ethylene carbonate (E)
C) and a mixture of diethyl carbonate (DEC) at an equal volume ratio to a mixture of lithium hexafluorophosphate (LiPF ₆ )
Was dissolved at 1 mol / liter).

Thereafter, the sealing body 15 is placed on the opening of the outer can 10 via the insulating gasket 16, and the upper end of the opening of the outer can 10 is caulked toward the sealing body 15 and sealed in a liquid-tight manner. And lithium secondary batteries A, B, C, D and E, respectively. The lithium secondary batteries A (using the outer can a), B (using the outer can b), C (using the outer can c), and D (using the outer can) prepared in this manner. d
), E (using the outer can e) are 65 mm in height, 18 mm in diameter and 1600 m in nominal capacity.
Ah.

6. Overdischarge test of non-aqueous electrolyte secondary battery Next, the battery voltage (voltage before standing) of each of the batteries A, B, C, D, and E prepared as described above and subjected to a predetermined charge / discharge test was measured. After that, each of these batteries A, B, C, D, E
Was discharged at room temperature (about 25 ° C.) at a constant current of 10 mA until the battery voltage reached 2.10 V. Then
After the open circuit voltage of the batteries has stabilized, each of these batteries A, B,
C, D, and E were left in a thermostat kept at 60 ° C.
After standing, the battery voltages after 20 days and 30 days have been measured, respectively, and these batteries A, B, C,
When the overdischarge characteristics of D and E were determined, the results were as shown in Table 2 below. A battery left in a thermostat at 60 ° C. for 20 days corresponds to a state left at room temperature (about 25 ° C.) for one year, and a battery left in a state left for 30 days at room temperature (about 25 ° C.). Equivalent to standing for 5 years.

[0034]

[Table 2]

As is evident from the results in Table 2, the voltage drop of the battery A using the outer can a (in which a composite plating layer composed of nickel metal and PVdF fine powder particles is formed on the inner surface) is remarkably reduced. It can be seen that the voltage drop of the battery B using the battery case B, which is small and then the outer can b (having a composite plating layer made of nickel metal and PTFE fine powder particles formed on the inner surface), is small. On the other hand, a battery E using an outer can e (having a PVdF layer formed thereon), a battery D using an outer can d (having a polypropylene sheet bonded thereto), and an outer can c (having a nickel metal layer formed thereon) It can be seen that the voltage drop increases in the order of the battery C using.

This is because, in the outer can c in which the nickel metal layer is formed on the surface of the outer can by plating, the nickel metal layer formed by plating is not perfect, and there are defects and the like. When grooving is performed on the outer can to caulk the sealing body, cracks occur in the nickel metal layer in the grooved portion, and corrosion current flows through these defects and cracks. It is thought that it became. Further, in the outer can d in which the polypropylene sheet is adhered to the inner surface, the inner surface of the outer can d cannot be completely covered with the polypropylene sheet,
It is considered that the corrosion current flowed through a portion not covered with the polypropylene sheet or a gap between the outer can and the polypropylene sheet. Further, in the outer can e having a PVdF layer formed on the inner surface, Nd in which PVdF is dissolved is used.
This is probably because the MP solution could not be uniformly applied to the inner surface of the outer can and current (corrosion current) flowed through the non-uniform portion.

On the other hand, in the outer can b in which a composite plating layer made of nickel metal and PTFE fine powder particles is formed on the outer can, the PTFE fine powder particles are uniformly adhered to the surface of the outer can together with the nickel metal to form a composite plating layer. It is considered that the uniform formation of the layer improved the corrosion resistance and suppressed the increase in the corrosion potential. Further, in the outer can a in which a composite plating layer composed of nickel metal and PVdF fine powder particles is formed on the outer can, the PVdF fine powder particles uniformly adhere to the surface of the outer can together with the nickel metal, and the composite plating layer becomes uniform. Although the reason is unknown, it is considered that the current (corrosion current) flowing through the outer can a was further reduced, probably because a plating layer better than PTFE was formed.

As described above, in the present invention, the composite plating layer 10a made of nickel metal and fluororesin fine powder particles such as PVdF fine powder or PTFE fine powder having excellent corrosion resistance is formed on the surface of the metal outer can 10. 10b, the corrosion resistance of the metal outer can 10 is improved, and even if the non-aqueous electrolyte secondary battery using such a metal outer can 10 is in an overdischarged state, the metal outer can 10 Corrosion current flowing through the can 10 can be suppressed, and long-term storage characteristics are improved.

A metal piece (nickel plate) 17 is welded to the inner surface of the bottom of the metal outer can 10, and the nickel plate 17
The negative electrode current collecting tab 12a extending from the negative electrode 12 of the electrode group is welded to the nickel plate 17 after the protective film 18 is applied and plated on the surface of the negative electrode 12 and the protective film 18 is peeled off. It is possible to prevent the occurrence of poor welding at the welding portion between the nickel plate 17 and the negative electrode current collecting tab 12a, and to obtain a nonaqueous electrolyte secondary battery with reduced internal resistance. . Further, a metal outer can 1
Since the plating is performed after the protective film 19 is also applied to the bottom outer surface of the metal outer can 10, the formation of a composite plating layer on the bottom outer surface of the metal outer can 10 serving as a negative terminal is prevented. Thus, a negative electrode terminal having excellent conductivity can be formed.

In the above-described embodiment, polyvinylidene fluoride (PV) is used as the fluororesin that coats the surface of the metal outer can 10 with nickel metal.
dF) or polytetrafluoroethylene (PTF)
Examples using E) have been described, but in addition to these, polychlorotrifluoroethylene (PCTFE), polyvinyl fluoride (PVF), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PF)
A), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-ethylene copolymer (E / TFE), chlorotrifluoroethylene-ethylene copolymer (E / CTFE), tetrafluoroethylene- Even if a fluororesin such as perfluorodimethyldioxol copolymer (TFE / PDD) is used, almost the same effect can be obtained.

Further, in the above-described embodiment, an example in which an iron outer can is used as the metal outer can has been described. Metal that does not alloy with lithium, due to the effect of the potential of the
Although the effects of the present invention can be achieved by using an alloy (for example, stainless steel), it is preferable to use an iron outer can in consideration of economy, workability, and the like.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a schematic configuration of a three-electrode electrochemical cell.

FIG. 2 is a view schematically showing a main part of a metal outer can; FIG. 2A is a cross-sectional view showing a metal outer can a of Example 1 and a metal outer can b of Example 2; Yes, FIG. 2 (b)
FIG. 2 is a sectional view showing a metal outer can c of Comparative Example 1, and FIG.
(C) is a sectional view showing a metal outer can d of Comparative Example 2 and a metal outer can e of Comparative Example 3.

FIG. 3 is a diagram schematically showing a schematic configuration of a nonaqueous electrolyte battery of the present invention.

FIG. 4 is a diagram schematically showing changes in negative electrode potential, positive electrode potential, and battery voltage when a nonaqueous electrolyte battery is overdischarged.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... working electrode, 2 ... counter electrode, 3 ... reference electrode, 4 ... working electrode lead, 5 ... counter electrode lead, 6 ... reference electrode lead, 7 ... glass cell container, 8 ... power supply with ammeter, 10 ... outer can, 10a ,
10b: composite plating layer, 10x: annular groove, 11: band-shaped positive electrode, 11a: positive electrode current collecting tab, 12: band-shaped negative electrode, 12a ...
Negative electrode current collecting tab, 13 ... separator (microporous film), 14 ...
Insulating plate, 15 ... sealing body, 16 ... insulating gasket, 17 ...
Nickel plate (metal piece)

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) H01M 10/40 H01M 10/40 Z F term (reference) 4K024 AA03 AB01 AB12 BA03 BB28 BC04 CA02 CA05 GA04 5H011 AA02 AA09 CC06 CC08 DD13 DD18 EE04 KK00 5H022 AA09 BB11 BB22 CC19 CC30 EE03 EE06 KK07 5H029 AJ13 AJ14 AK03 AL07 AM03 AM05 AM07 BJ02 CJ05 CJ24 DJ02 DJ05 EJ01 EJ12 HJ12

Claims (8)

[Claims] An electrode group comprising a negative electrode capable of inserting and extracting lithium ions and a positive electrode capable of inserting and extracting lithium ions via a separator, and a lithium salt as a solute in an organic solvent. A non-aqueous electrolyte secondary battery including a metal outer can containing a dissolved non-aqueous electrolyte, comprising a composite plating layer made of nickel metal and fluororesin fine powder particles on a surface of the metal outer can. A non-aqueous electrolyte secondary battery characterized in that: 2. A part of an inner surface of a bottom of the metal outer can does not include the composite plating layer, and a metal piece is fixed to a part not including the composite plating layer, and the electrode group is attached to the metal piece. The non-aqueous electrolyte secondary battery according to claim 1, wherein a current collection tab extending from the negative electrode is fixed. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the fluororesin is polyvinylidene fluoride (PVdF). 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the metal outer can is an iron outer can. 5. A lithium salt as a solute in an electrode group in which a negative electrode capable of occluding and releasing lithium ions and a positive electrode capable of occluding and releasing lithium ions are opposed via a separator, and an organic solvent. A method for manufacturing a non-aqueous electrolyte secondary battery including a metal outer can containing a dissolved non-aqueous electrolyte, wherein the metal is placed in a plating bath in which fine particles of fluororesin are dissolved in an aqueous solution in which nickel metal is dissolved. A plating step of forming a composite plating layer composed of nickel metal and fine particles of fluororesin on the surface of the metal outer can by immersing the outer can made by electroplating and forming a composite plating layer on the surface of the metal outer can. A method for producing a water electrolyte secondary battery. 6. A welding step in which a metal piece is previously welded to a bottom inner surface of the metal outer can before the plating step, and a metal piece welded to the bottom inner surface of the metal outer can is The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 5, further comprising a step of applying an internal protective film for applying a protective film. 7. The method according to claim 1, further comprising the step of: after peeling off the protective film adhered to the surface of the metal piece, welding a current collecting tab extending from a negative electrode of the electrode group to the metal piece. The method for producing a non-aqueous electrolyte secondary battery according to claim 6. 8. The method according to claim 5, further comprising, before the plating step, an external protective film applying step of applying a protective film on a bottom outer surface of the metal outer can in advance. Item 8. The method for producing a nonaqueous electrolyte secondary battery according to any one of Items 7.