JP2003100278A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve recovery of a battery capacity after a high output and excessive discharge. SOLUTION: A nonaqueous electrolyte secondary battery comprises: a metal lead tab electrically connecting an anode and a conducive case has a multilayer structure comprising copper or a copper alloy, and the multilayer structure comprises nickel or a nickel alloy as the second layer being in contact with the conductive case working as an anode terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a high power type non-aqueous electrolyte secondary battery having excellent over-discharge resistance.

[0002]

2. Description of the Related Art In recent years, lithium ion secondary batteries and polymer lithium secondary batteries using non-aqueous electrolytes have been widely used in electronic devices such as mobile phones. These secondary batteries are characterized by being lighter in weight than conventional nickel-cadmium batteries and nickel-hydrogen batteries and having high electromotive force of 4 V class, and their excellent performance is drawing attention.

Therefore, recently, the idea of using this lithium secondary battery as a power source for a motor drive device has been activated. In such applications, higher output characteristics are required as compared with conventional lithium secondary batteries.

In order to increase the output of a battery, it is necessary to reduce the internal resistance of the battery as much as possible. For that purpose, it is important to reduce the resistance of the electrode and the battery member to improve the current collection efficiency.

By the way, the conventional lithium ion battery is
Aluminum foil is used for the positive electrode current collector, and copper foil is used for the negative electrode current collector, and the battery active material is applied and fixed onto each current collector, and the separator, the negative electrode, the separator, the positive electrode, and the separator are wound and laminated in this order. The electrode group, which is the wound power generation element, is housed in a metal case. In particular, the cylindrical lithium-ion battery has excellent productivity and mass productivity, and because of the shape of the wound structure, the battery electrode reaction is likely to occur uniformly regardless of the electrode site. It has become the center. Figure 4
FIG. 7 is a cross-sectional view illustrating a conventional cylindrical battery. The cylindrical battery includes a positive electrode sheet 7 in which a positive electrode active material is applied to a positive electrode aluminum foil current collector and a negative electrode copper foil current collector (not shown) in a metal case 4 which also serves as a negative electrode terminal. (Not shown)
It is composed of an electrode group 6 which is a power generation element formed by laminating and winding a negative electrode sheet 9 formed by coating with a separator 8 having a width larger than that of the positive electrode sheet 7. A strip of nickel-made negative electrode lead tab 15 on the copper foil on the winding terminal side of the negative electrode sheet 9.
Are connected by ultrasonic welding or the like, and the other side of the negative electrode lead tab 15 is joined by resistance welding or the like to the bottom portion of the metal case 4 of the metal case which also serves as the negative electrode terminal. In addition, a battery lid 11 also serving as a positive electrode terminal is provided above the conductive metal case 4.
When the abnormal pressure rises inside the battery, the safety valve plate 1 having a current cut-off function that releases the internal pressure and shuts off the current path and a pressure release function that releases the pressure is pressed against the inside of the battery. A strip-shaped aluminum positive electrode lead tab 13 is connected and sealed by laser welding or the like on an aluminum foil on the winding start end side of the positive electrode sheet 7 on the wall plate. Here, 3 is a metal ring, 5 is a bottom insulating plate, 10 is a sealing body,
Reference numeral 12 is a sealing insulator (gasket).

However, when nickel is used as the negative electrode lead tab as in this battery, there is a problem that a large voltage drop (IR loss) occurs when a large current continuous discharge is performed and output characteristics are deteriorated.

Therefore, a method of using copper, which has a lower resistance, instead of nickel as the negative electrode lead tab has been studied.

However, such a battery is over-discharged due to misuse, dark current of an electronic circuit of equipment in which the battery is used, consumption current of a battery protection circuit, etc. The copper as the current collector of the negative electrode and the copper lead tab of the negative electrode are eluted as copper ions in the electrolytic solution by the dissolution reaction of copper as shown in the following formula (1).

[0009] ^{Cu → Cu 2+ + 2e - ·} · ························· (1) the current collector of the negative electrode by the dissolution of the copper The current path between the body and the copper lead tab portion is reduced, and the output characteristics are significantly reduced.
Further, as the elution of copper further progresses, the copper lead tab breaks, and there is a problem that the battery does not function as a battery.

Further, the eluted copper is deposited on the surface of the positive electrode and breaks through the separator to cause a short circuit. In such a state, there is a problem that it cannot be used as a battery because it does not recover even if it is charged again.

[0011]

As described above, in the conventional lithium ion battery using copper as the negative electrode lead tab, it is poled when it is in an overdischarged state, and copper and the negative electrode which are current collectors of the negative electrode. Since the copper lead tab of No. 1 causes a dissolution reaction and elutes in the electrolytic solution, the current path decreases and output characteristics deteriorate, and further elution of copper causes breakage and short circuit of the copper lead tab, resulting in a battery. There is a problem that it will not work.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a high output type non-aqueous electrolyte secondary battery which is excellent in capacity recovery even in the event of an over-discharge state.

[0013]

The present invention has been made to solve the above problems. That is, the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material is a positive electrode formed on the positive electrode current collector, a separator containing a non-aqueous electrolyte formed adjacent to the positive electrode, and the positive electrode A negative electrode having a negative electrode active material formed on a negative electrode current collector facing each other with a separator interposed therebetween, the positive electrode, the separator, and a conductive case containing the negative electrode, and the conductive case and the negative electrode current collector. A non-aqueous electrolyte secondary battery comprising a metal lead tab material electrically connected, wherein the metal lead tab material has a multilayer structure including a first layer of copper or copper alloy and a second layer of nickel or nickel alloy, The second layer is in electrical contact with the conductive case that also serves as a negative electrode terminal.

Further, the non-aqueous electrolyte secondary battery of the present invention is the above-mentioned invention, wherein the metal lead tab material is the second one.
A multilayer structure in which a layer, the first layer, and a third layer of nickel or nickel alloy are sequentially stacked, and the third layer is directly electrically connected to the negative electrode. .

With this structure, the voltage drop (IR loss) at the lead tab portion is small, so that the output is high, and even if the battery should be over-discharged, the copper dissolution reaction is unlikely to occur. It is possible to improve the capacity recovery during over-discharge.

As the copper alloy of the metal lead tab material,
Specifically, a copper-nickel alloy, a copper-iron alloy, a copper-silver alloy, a copper-phosphorus alloy, etc. are mentioned.

The content of the additional element in the copper alloy is
It is preferably 1% by weight or less. More preferably, it is 0.05% by weight or less. If the content of the additive element exceeds this range, the electrical conductivity may decrease, and high output characteristics may be impaired.

The content of the additional element in the nickel alloy is preferably 1% by weight or less for the same reason. Further, in the metal lead tab material, the thickness of the first layer made of copper or copper alloy. Is T ₁ , and the thicknesses of the second and third layers made of nickel or nickel alloy are T ₂ and T ₃ , respectively, T ₂ = T ₃ and (T ₂ + T ₃ ) / T ₁ ≦ 1 In that case, high output characteristics can be obtained, which is preferable.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a non-aqueous electrolyte secondary battery according to the present invention (for example, a cylindrical non-aqueous electrolyte secondary battery) will be described below with reference to FIG. (Form of Metal Lead Tab Material According to the Present Invention) First, the metal lead tab material 14 according to the present invention will be described in detail. Reference numeral 14 denotes a metal lead tab material, and a negative electrode current collector (not shown) housed in the electrode group 6 and a conductive metal case 4
It has a multi-layer structure that electrically connects to each other. The negative electrode lead tab 14 is made of a strip-shaped material having a total thickness of 0.1 mm and a width of 4 mm, and a first layer 14-2 made of a copper plate having a width of 4 mm and a thickness of 50 μm and a second layer of nickel having a thickness of 25 μm.
A three-layer structure is formed by sandwiching the layer (layer on the drawing) and the third layer (layer on the drawing) 14-1 from both sides. As described above, in the multilayer structure negative electrode lead tab, it is desirable to dispose a material having a large specific resistance value on the side in contact with the metal case 4. In this three-layer structure, the material is on the nickel layer side, and the negative electrode lead tab 14 and the metal case are arranged. With the connection method by resistance welding with No. 4, excellent weldability (strength, workability) can be exhibited. The method for forming the multilayer structure is not particularly specified, and for example, electroless and electrolytic plating of nickel on a copper plate, the second layer and the third layer of the first layer copper plate and the nickel plate, A method using clad processing may be used. The cross-sectional structure is preferably a multi-layer structure without being restricted to a three-layer structure. Where this first
Another metal such as an alloy of copper and nickel, gold, silver, or an alloy of two or more of these metals may be interposed between the layers, the second layer, and the third layer. (Form of Non-Aqueous Electrolyte Secondary Battery According to Embodiment of the Present Invention) FIG. 1 is a cross-sectional view showing a non-aqueous electrolyte secondary battery according to a most preferable embodiment of the present invention. The same parts as those of the conventional non-aqueous electrolyte secondary battery described with reference to FIG. 4 are designated by the same reference numerals except important parts, and detailed description thereof will be omitted.

For example, in a metal case 4 made of nickel-plated iron which also serves as a negative electrode terminal, a positive electrode sheet 7 and a negative electrode copper foil in which a positive electrode active material is applied and formed on a positive electrode aluminum foil so as to widen the electrode reaction area. A negative electrode sheet 9 having a negative electrode active material applied thereon is laminated and wound with a width larger than the negative electrode sheet and larger than the negative electrode sheet with a thin separator 8 interposed between the electrode group 6 and the electrode group 6. The separator 8 is formed of, for example, a non-woven fabric, a polypropylene microporous film, a polyethylene microporous film, or a polyethylene-polypropylene microporous laminated film. The strip-shaped multi-layered structure negative electrode lead tab 14 whose main constituent is copper is connected to the copper foil on the winding terminal end side of the negative electrode sheet 9 by ultrasonic welding or the like, and the other of the negative electrode lead tabs 14 is a negative electrode terminal. It is joined to the bottom of the double metal case by resistance welding. In addition, on the upper part of the metal case, the battery lid 11 also serving as the positive electrode terminal has a current cut-off function for releasing the internal pressure to cut off the current path and a pressure release function for releasing the pressure when the pressure inside the battery is abnormally increased. The safety valve plate is pressure-welded, and a strip-shaped aluminum positive electrode lead tab 13 is formed on the aluminum foil on the winding start end side of the positive electrode sheet 7 by laser welding or the like on the wall plate located on the battery inner side of the safety valve plate. To be done.

Next, the positive electrode 7, the negative electrode 9 and the separator 8
The electrolytic solution impregnated inside will be specifically described. a) Positive electrode 7 For the positive electrode 7, for example, a positive electrode mixture coating liquid obtained by dispersing a positive electrode active material, a conductive agent and a binder in an appropriate solvent is applied to one side or both sides of a positive electrode current collector made of a metal foil. It is produced by

As the positive electrode active material, LiCoO ₂ or composition formulas LiCo _1-x M _x O ₂ and LiNi _1-x M _x O ₂ (where M is at least one element and x is 0 <x ≦ 0 .5)
A lithium mixed metal oxide represented by can be used. Specifically, LiCo _{1- x} Ni _x O ₂ , LiNi _1-x C
_{o x O 2, LiNi 1-} xy Co x B y O 2, LiNi 1-xy C
_{o x Al y O 2, LiNi} 1-xy Co x Mn y O 2, LiNi
_1-xy Co _x Sn _y O _{2 and the} like can be mentioned. (X, y
Is 0 <x ≦ 0.5, 0 ≦ y <0.5, and 0 <x + y ≦
Also, a mixture of two or more of these lithium mixed metal oxides may be used.

As the conductive agent, for example, acetylene black, carbon black, artificial graphite or natural graphite can be used.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), hydrogen or fluorine of PVdF, and
Modified PVdF in which at least one is substituted with another substituent,
A copolymer of vinylidene fluoride-6-fluorinated propylene, a ternary copolymer of polyvinylidene fluoride-tetrafluoroethylene-6-propylene fluoride, or the like can be used.

As the organic solvent for dispersing the binder, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF) and the like are used.

The metal foil current collector has a thickness of 10 to 10, for example.
Examples include 30 μm aluminum foil, stainless steel foil, titanium foil, and the like.

B) Negative Electrode 9 The negative electrode 9 is made of, for example, a carbonaceous material that absorbs and releases lithium ions or a material containing a chalcogen compound, a light metal, or the like. Above all, a negative electrode containing a carbonaceous material or a chalcogen compound that occludes / releases lithium ions is preferable because battery characteristics such as cycle life of the secondary battery are improved.

Examples of the carbonaceous material which occludes / releases lithium ions include coke, carbon fiber, pyrolytic vapor-phase carbonaceous material, graphite, resin fired body, mesophase pitch carbon fiber or mesophase spherical carbon fired body. You can Above all, it is preferable to use mesophase pitch carbon fiber or mesophase spherical carbon graphitized at 2500 ° C. or higher because the electrode capacity increases.

Examples of chalcogen compounds that absorb and release lithium ions include titanium disulfide (TiS ₂ ), molybdenum disulfide (MoS ₂ ), and niobium selenide (NbSe ₂ ).
And so on. When such a chalcogen compound is used for the negative electrode, the voltage of the secondary battery drops, but the capacity of the negative electrode increases, so that the capacity of the secondary battery is improved. Further, since the negative electrode has a high diffusion rate of lithium ions, the rapid charge / discharge performance of the secondary battery is improved.

Examples of the light metal include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like.

The negative electrode (for example, a negative electrode made of a carbon material) is, specifically, a negative electrode mixture obtained by dispersing a carbon material, a conductive agent and a binder in an appropriate solvent, on one side of a current collector made of a metal foil. Alternatively, it is prepared by coating on both sides.

Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PV).
dF), ethylene-propylene-diene copolymer (EP
DM), styrene-butadiene rubber (SBR) and the like can be used.

As the metal foil current collector, for example, copper foil, nickel foil and the like can be used. However, in consideration of electrochemical stability and flexibility during winding, copper foil is most preferable and electrolytic Can be used with copper, electroless copper, and with or without gloss. It can be used similarly to copper in a copper alloy. In this case, copper, metal such as nickel, iron, etc.
Copper alloy can be obtained by adding about 05% by weight. On the other hand, the thickness of the foil at this time is preferably 6 μm or more and 20 μm or less.

C) Electrolyte The electrolytic solution has a composition in which an electrolyte is dissolved in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), such as dimethyl carbonate (D).
Chain carbonate such as MC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC),
Chain ethers such as 1,2-dimethoxyethane (DME) and diethoxyethane (DEE), tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-Me
THF) and other cyclic ethers and crown ethers, γ-
At least one selected from fatty acid esters such as butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfur compounds such as sulfolane (SL) and dimethyl sulfoxide (DMSO) can be used.

Among them, at least one selected from EC, PC and γ-BL, EC, PC and γ-B
At least one selected from L and DMC, MEC, DE
It is desirable to use a mixed solvent containing at least one selected from C, DME, DEE, THF, 2-MeTHF, and AN. Further, when a negative electrode containing a carbonaceous material that absorbs and releases the lithium ions is used, from the viewpoint of improving the cycle life of the secondary battery including the negative electrode, EC and PC and γ-BL, and EC and PC are used. MEC, EC
And PC and DEC, EC and PC and DEE, EC and AN, E
C and MEC, PC and DMC, PC and DEC, or EC
It is desirable to use a mixed solvent consisting of and DEC.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (LiP).
F ₆ ), lithium borofluoride (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ]
Examples thereof include lithium salts. Above all, LiP
If F ₆ , LiBF ₄ , and LiN (CF ₃ SO ₂ ) ₂ are used,
It is preferable because conductivity and safety are improved.

The amount of the electrolyte dissolved in the non-aqueous solvent was 0.
It is preferably in the range of 5 mol / L to 2.0 mol / L.

As described above in detail, in the non-aqueous electrolyte secondary battery according to the present invention using the metal lead tab material having the above-mentioned multilayer structure, the voltage drop (IR loss) at the lead tab portion is small, and by any chance Since the dissolution reaction of copper is unlikely to occur even in the overdischarge state, a non-aqueous electrolyte secondary battery with high output and excellent capacity recovery can be obtained.

In the above-mentioned embodiment, the example applied to the cylindrical non-aqueous electrolyte secondary battery has been described, but the present invention can also be applied to the rectangular non-aqueous electrolyte secondary battery.

[0041]

EXAMPLES The details of the present invention will be described below with reference to examples.

(Embodiment 1) This embodiment 1 relates to a lithium ion secondary battery having the structure shown in FIG. 1, and the battery structure and its characteristics will be described in detail along with its manufacturing procedure.

Polyvinylidene fluoride was added to N-methyl-2-
LiCoO ₂ powder (average particle size: 10 μm), acetylene black as a conductive agent, and artificial graphite were added to a solution dissolved in pyrrolidone, and the mixture was stirred and mixed to obtain LiCoO ₂
A positive electrode mixture coating liquid composed of 90.3% by weight, acetylene black 2.5% by weight, artificial graphite 3% by weight, and polyvinylidene fluoride 4% by weight was prepared. This positive electrode mixture coating liquid is applied to both sides of an aluminum foil (1N30, thickness 20 μm),
After drying, a positive electrode 7 was prepared by pressure molding using a rolling mill so that the mixture layer of the positive electrode had a porosity of 25%.

On the other hand, the mesophase pitch carbon fiber (MCF) made from mesophase pitch was carbonized at 1000 ° C. in an argon gas atmosphere, and then the average fiber length was 30 μm.
m, an average fiber diameter of 11 μm, a particle size of 1 to 80 μm, and 90% by volume, and appropriately pulverized so that particles having a particle size of 0.5 μm or less become 5% or less, and then 3000 ° C. in an argon atmosphere. A carbonaceous material was produced by graphitizing with. Then, polyvinylidene fluoride was added to N-methyl-
A carbonaceous material and artificial graphite are added to a solution dissolved in 2-pyrrolidone, and the mixture is stirred and mixed, and the negative electrode mixture composition is 86.5% by weight of carbonaceous material, 9.5% by weight of artificial graphite, and 4% by weight of polyvinylidene fluoride. A mixture coating solution was prepared. This is copper foil (N
(C-WS, thickness 12 μm) was applied on both surfaces, dried and then pressure-molded by a rolling mill to prepare a negative electrode having a thickness of 124 μm. At this time, the ratio (capacity balance) of the negative electrode design counter electrode capacity to the positive electrode design capacity after molding is
The packing density and the electrode length were adjusted so as to be 1.05 or more and 1.15 or less.

The negative electrode lead tab 14 is made of a strip material having a total thickness of 0.1 mm and a width of 4 mm, and has a width of 4 mm.
A three-layer structure in which the first layer consisting of a 50 μm thick copper plate is sandwiched from both sides by a second layer and a third layer of nickel with a thickness of 25 μm (clad processed product of nickel 14-1 and copper 14-2) Was used. After welding this with an ultrasonic welding machine, a positive electrode, a separator made of a polyethylene porous film, and a negative electrode were laminated in this order, and were spirally wound so that the negative electrode was located outside. At this time, the positive electrode and the negative electrode were provided with a portion where the active material was not applied and mounted on the front and end portions of the electrode, and the electrode group 6 was produced by winding.

The electrode group 6 is housed in the bottomed cylindrical container 4, the negative electrode lead 14 is resistance welded to the bottom of the bottomed cylindrical container 4, and the positive electrode lead 13 is the positive electrode terminal of the bottomed cylindrical container 4. Laser sealing connection was made to the sealing body 10 arranged at 11.

Subsequently, in a bottomed cylindrical container 4, lithium hexafluorophosphate (LiPF ₆ ) was added to a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (mixing volume ratio 1: 2). A 1 M dissolved non-aqueous electrolytic solution was injected to sufficiently impregnate the electrode group with the non-aqueous electrolytic solution.

The bottomed cylindrical container 4 is loaded with the positive electrode terminal 11 and the pressure release valve (rupture) 1 via the insulator (glass, resin or ceramics) 12 and together with the bottomed cylindrical container 4. By the sealing body 10, the sealing body 10
The entire circumference of the boundary was sealed and sealed by a mechanical caulking structure. It has a structure in which a current cutoff valve mechanism having a breaking pressure of 15 kg / cm 2 and a pressure release valve (rupture) 1 mechanism having a breaking pressure of 20 kg / cm 2 provided with a thin portion in advance is provided.

As described above, the design rated capacity 1600
A mAh cylindrical non-aqueous electrolyte secondary battery (18650 size (diameter 18 mm, height 65 mm)) was assembled.

Example 2 As the negative electrode lead tab 14,
Made of strip-shaped material with a total thickness of 0.1 mm and a width of 4 mm,
The thickness of the first layer made of a copper plate having a width of 4 mm and a thickness of 30 μm is 3 mm.
A design rated capacity of 1600 mA was obtained in the same manner as in Example 1 except that a three-layer structure (clad processed product) sandwiched from both sides by a second layer and a third layer of 5 μm nickel was used.
A cylindrical non-aqueous electrolyte secondary battery (18650 size (diameter 18 mm, height 65 mm)) of h was assembled.

Example 3 As the negative electrode lead tab 14,
Made of strip-shaped material with a total thickness of 0.1 mm and a width of 4 mm,
Copper-nickel alloy with a width of 4 mm and a thickness of 50 μm (nickel:
(0.05% by weight), except that a three-layer structure (clad processed product) in which a first layer made of a plate was sandwiched from both sides by a second layer and a third layer of nickel having a thickness of 25 μm was used. Cylindrical non-aqueous electrolyte secondary battery (18650 size (diameter 18 m
m, height 65 mm)) was assembled.

Example 4 As the negative electrode lead tab 14,
Made of strip-shaped material with a total thickness of 0.1 mm and a width of 4 mm,
A three-layer structure in which a first layer made of a copper-iron-gold (iron: 0.05% by weight) plate having a width of 4 mm and a thickness of 50 μm is sandwiched from both sides by a second layer and a third layer of nickel having a thickness of 25 μm ( A cylindrical non-aqueous electrolyte secondary battery (18650 size (diameter 18 mm, height 65 mm) having a design rated capacity of 1600 mAh was used in the same manner as in Example 1 except that a clad processed product) was used.
mm)) was assembled.

Example 5 As the negative electrode lead tab 14,
Made of strip-shaped material with a total thickness of 0.1 mm and a width of 4 mm,
The first layer made of a copper plate having a width of 4 mm and a thickness of 50 μm has a thickness of 2 mm.
In the same manner as in Example 1 except that a three-layer structure (clad processed product) sandwiched from both sides by a second layer and a third layer of a 5 μm nickel-copper alloy (copper: 1% by weight) was used. Cylindrical non-aqueous electrolyte secondary battery with design rated capacity of 1600 mAh (18650 size (diameter 18 mm, height 65 m
m)) was assembled.

Example 6 As the negative electrode lead tab 14,
The same procedure as in Example 1 was performed except that a three-layer structure (electroless plating processed product) having a thickness of 2 μm and having a thickness of 2 μm applied to both sides and sides of a copper plate having a width of 4 mm and a thickness of 0.1 mm was used. Cylindrical non-aqueous electrolyte secondary battery with a design rated capacity of 1600 mAh (18650 size (diameter 18 mm, height 65
mm)) was assembled.

Example 7 As the negative electrode lead tab 14,
The same procedure as in Example 1 was performed except that a three-layer structure (electroless plating processed product) in which a copper plate having a width of 4 mm and a thickness of 0.1 mm was plated with nickel having a thickness of 1 μm was used. Cylindrical non-aqueous electrolyte secondary battery with a design rated capacity of 1600 mAh (18650 size (diameter 18 mm, height 65
mm)) was assembled.

Example 8 As the negative electrode lead tab 14,
Designed in the same manner as in Example 1 except that a three-layer structure (electrolytically plated processed product) in which a copper plate having a width of 4 mm and a thickness of 0.1 mm and having a thickness of 2 μm was plated on both sides and side surfaces was used. Cylindrical non-aqueous electrolyte secondary battery (18650 size (diameter 18 mm, height 65 m
m)) was assembled.

(Comparative Example 1) Material is copper (thickness 0.1 mm)
Example 1 except that a negative electrode lead tab consisting of
Non-aqueous electrolyte secondary battery (18650 size)
Assembled.

(Comparative Example 2) The material is nickel (thickness: 0.1).
mm non-aqueous electrolyte secondary battery (18650 size) was assembled in the same manner as in Example 1 except that the negative electrode lead tabs were used.

A predetermined number of the non-aqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 and 2 obtained as described above were prepared and the output characteristics were evaluated. As a method of defining this output characteristic, here, a method of defining the ratio of each discharge capacity obtained when discharging at two current values is adopted. That is, when the current of 1600 mA that discharges 1600 mAh, which is the nominal capacity of a battery, in 1 hour is 1 C, the discharge capacity (0.2 C) when discharged at 0.2 C, 5
The discharge capacity (5C) when discharged at C was measured,
The value of discharge capacity (5C) / discharge capacity (0.2C), which is the ratio of the two discharge capacities, is defined as the large current discharge capacity ratio, and will be used in the following text. At this time, charging is 0.2
Charging was performed up to 4.2 V with a current value of C, and constant current-constant voltage charging with a constant voltage of 4.2 V was performed for a total of 8 hours. The values of the large current discharge capacity ratio are shown in Table 1.

As is clear from Table 1, Examples 1 to 8 using the negative electrode lead tab having the multilayer structure according to the present invention and Comparative Example 1 using the negative electrode lead tab made of copper.
It was confirmed that each of the large current discharge ratios was 90% or more and the output characteristics were excellent.

On the other hand, Comparative Example 2 using the nickel lead tab had a large current discharge ratio of less than 90%, which was not so good as compared with Examples 1 to 8 and Comparative Example 1.

Next, Examples 1 to 8 and Comparative Examples 1 to
With respect to each battery of Comparative Example 2, an over-discharge test was performed assuming an over-discharged state. In the over-discharge test, continuous discharge was forcibly performed at a current value of 1 mA.

FIG. 2 shows the discharge time and the battery voltage characteristic in the overdischarge test for Examples 1 and 2. As shown in FIG. 2, in the battery of Example 1, 30
It was possible to continue discharging without changing the polarity of the battery voltage even if the time was exceeded.

On the other hand, in the battery of Comparative Example 1, it was shown that the polarity inversion occurred after about 5 hours, and it was clearly put into an excessively overdischarged state. In particular, it can be seen that the polarization state is 1 V or more 8 hours before.

Next, after the over-discharge test, the batteries of Examples 1 to 8 and Comparative Examples 1 and 2 were recharged to examine their capacity recoverability. FIG. 3 shows Example 1 and Comparative Example 1.
Regarding the behavior characteristics of charging time and charging current after the over-discharge test.

As shown in FIG. 3, in the battery of Example 1, the battery voltage was gradually increased from the start of charging, and the fully charged state could be reached after 2 hours.

On the other hand, in the battery of Comparative Example 1, the battery voltage did not rise at all because of the reversal of the polarity, and the function as the secondary battery could not be obtained.

The results of examining the capacity recoverability as described above are also shown in Table 1. As an evaluation rank, 100 test samples were prepared in each of the examples and expressed as a ratio to 100 batteries whose capacity was normally restored after an overcharge test. A rank is 100% to 90% or more, and B rank is Is 9
Less than 0%, 80% or more, and C rank less than 80%.

As is clear from Table 1, the batteries of Examples 1 to 8 using the negative electrode lead tab having the multilayer structure according to the present invention were very excellent in capacity recovery.

On the other hand, the battery of Comparative Example 1 using the copper negative electrode lead tab had extremely poor capacity recovery. (Comparative Example 3) As a negative electrode lead tab, the total thickness is 0.1 m.
made of strip-shaped material with a width of 4 mm and a width of 4 mm and 50 μm
A three-layer structure (clad processed product) was used in which a first layer made of an m-thick nickel plate was sandwiched from both sides by a second layer and a third layer of copper having a thickness of 25 μm. This is welded to the negative electrode current collector by an ultrasonic welding machine in the same manner as in Example 1, and then the positive electrode, the separator made of a polyethylene porous film and the negative electrode are laminated in this order, and the negative electrode is located outside. Thus, the electrode group was produced by spirally winding.

This electrode group was housed in a cylindrical container with a bottom,
Example 1 The negative electrode lead is provided on the bottom of the bottomed cylindrical container.
I tried to perform resistance welding under the same conditions as above, but could not weld. Therefore, the welding output (voltage or current, and time) of the resistance welding machine was increased and the operation was performed again, but the welding was still unsuccessful.

[0072]

[Table 1]

[0073]

As described in detail above, according to the present invention,
Even if the battery is in the over-discharged state, the dissolution reaction of copper hardly occurs, so that it is possible to provide a non-aqueous electrolyte secondary battery having excellent capacity recovery.

[Brief description of drawings]

FIG. 1 is a sectional view of a battery according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating discharge characteristics of Example 1 and Comparative Example 1 of the present invention.

FIG. 3 is a diagram illustrating charging characteristics of Example 1 and Comparative Example 1 of the present invention.

FIG. 4 is a cross-sectional view showing a conventional battery.

[Explanation of symbols]

1 ... Metal rupture plate with rupture function 3 ... Metal ring 4 ... Metal case (container) 5 ... Bottom insulation plate 6 ... Electrode group 7 ... Positive electrode 8: Separator 9 ... Negative electrode 10 ... Sealing body 11 ... Positive electrode terminal 12 ... Insulator for sealing (gasket) 13 ... Positive electrode lead tab 14 ... Negative electrode lead tab

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Motoko Kanda             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F-term (reference) 5H022 AA09 CC08 CC19 CC23 CC30                       EE01 EE03

Claims (2)

[Claims] 1. A positive electrode having a positive electrode active material formed on a positive electrode current collector, a separator formed adjacent to the positive electrode and containing a non-aqueous electrolyte, and a negative electrode active material facing the positive electrode through the separator. A negative electrode having a substance formed on a negative electrode current collector, a conductive case accommodating the positive electrode, the separator, and the negative electrode, and a metal lead tab material electrically connecting the conductive case and the negative electrode current collector. And a metal lead tab material having a multilayer structure including a first layer of copper or a copper alloy and a second layer of nickel or a nickel alloy, the second layer serving as a negative electrode terminal. A non-aqueous electrolyte secondary battery, which is in electrical contact with the electrically conductive case that also serves as a battery. 2. The metal lead tab material has a multi-layer structure in which the second layer, the first layer, and a third layer of nickel or nickel alloy are sequentially laminated, and the third layer is the The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is directly electrically connected to the negative electrode.