WO2000042669A1 - Lithium secondary cell - Google Patents

Abstract

A lithium secondary cell comprising a positive electrode (10') capable of releasing and capturing lithium ions, a negative electrode (20') made of a material capable of being doped with lithium ions and being dedoped of lithium ions, metallic lithium, or a lithium alloy, and an electrolyte allowing migration of lithium ions, wherein at least either the positive electrode (10') or the negative electrode (20') is formed on a current collector (11') having an insulating resin layer (12') and a metal conductive layer (13') formed on the resin layer (12'), the thickness of the metal conductive layer (13') is 2.5 to 5 νm, and through holes (14') are preferably made through at least the metal conductive layer (13') in the direction of the thickness thereof.

Description

 Satsuki Itoda »Lithium secondary battery technology

 The present invention relates to a lithium secondary battery used as a power source for holding a memory of an electronic device and a power source for driving a portable electronic device. Background art

 In recent years, primary batteries using lithium salt as an electrolyte have attracted attention because of their high energy density at high voltage (3 to 4 V) and have been put to practical use. In the future, in order to promote the portable use of personal computers, personal computers, mobile phones, etc., the development of high-performance secondary lithium batteries is desired.

 Lithium secondary batteries are composed of a positive electrode capable of charging and discharging lithium ions, a material capable of doping and undoping lithium ions, a negative electrode made of lithium metal or an alloy thereof, and an electrolyte that allows lithium ions to move. Has a non-aqueous electrolyte in which a lithium salt is dissolved in an organic solvent), and the positive electrode and the negative electrode are usually formed on a current collector.

 However, lithium secondary batteries have a very high energy density and generally use an organic solvent for the electrolyte, so that the batteries can be compressed (for example, crushed by heavy objects). Severe conditions such as nail penetration (for example, if a nail is accidentally hit with a battery during packing), an internal short circuit, high temperature exposure, or an external short circuit can cause a sudden temperature rise inside the battery, and in some cases, There is a problem such as ignition and burning (thermal runaway).

Attempts to solve this problem include, for example, the invention described in Japanese Patent Application Laid-Open No. 54-512157 and Japanese Patent Application Laid-Open No. 59-207230. There is a method of providing a porous separator between the positive electrode and the negative electrode. These inventions make use of the property that the material constituting the separator melts at the melting point and closes the pores. As a result, the ion flow between the positive electrode and the negative electrode is interrupted, and the current flows between the electrodes. As a result, the rise in temperature is suppressed.

 However, in a lithium secondary battery provided with a porous separator, thermal runaway can only be prevented on the premise that the separator is maintained in an appropriate state. Therefore, when the separator is broken due to the compression of the battery and the positive electrode and the negative electrode come into direct contact, or when the positive electrode and the negative electrode are short-circuited through a nail penetrating the separator when the nail is pierced, Runaway cannot be properly prevented.

 In consideration of such circumstances, for example, Japanese Patent Application Laid-Open No. 9-120818 and Japanese Patent Application Laid-Open No. 9-1213338 disclose a metal conductor layer on the surface of an insulating resin layer. A method is disclosed in which at least one of a positive electrode and a negative electrode is formed on a current collector on which is formed. In these inventions, the thickness of the metal conductor layer is set in the range of 0.05 to 2 μm, and the thickness (cross-sectional area) of the conductor portion in the current collector is reduced. Indeed, if a current collector with such a configuration is adopted, even if the separator is broken by the compression of the battery or the nail penetrates through the separator and the positive and negative electrodes are short-circuited, Since the cross-sectional area of the conductor in the current collector is small, the amount of current flowing between the positive electrode and the negative electrode during a short circuit is reduced. As a result, it is expected that the amount of heat generated during a short circuit will be reduced, the temperature inside the battery will be suppressed from rising, and thermal runaway will be avoided. However, if the force <, if the thickness of the conductor part is reduced, the electric resistance of the current collector increases, and the problem that the charge / discharge capacity of the battery decreases may occur. Therefore, an object of the present invention is to provide a lithium secondary battery that can solve the above-described problems. Disclosure of the invention

In order to solve the above-mentioned problems, the present invention provides a positive electrode capable of charging and discharging lithium ions, a negative electrode made of a material capable of doping and undoping lithium ions, a lithium metal or a lithium alloy, and a method of transferring lithium ions. A lithium secondary battery comprising: an electrolyte that allows the following; and at least one of the positive electrode and the negative electrode is formed on a current collector having a metal conductor layer formed on the surface of an insulating resin layer. A lithium secondary battery is provided, wherein the thickness of the metal conductor layer is 2.5 to 5 // m. In a lithium secondary battery having this configuration, a current collector having a configuration in which a metal conductor layer is formed on the surface of an insulating resin layer is employed, and the thickness of the conductor portion (cross-sectional area) of the current collector is reduced. Therefore, even if the battery is compressed and the current collector is broken or the nail is pierced or the nail is short-circuited between the positive electrode and the negative electrode, the amount of short-circuit current between the positive electrode and the negative electrode is not so large.

 And, since the current collector has an insulating resin layer, for example, when the current collector is sheared due to compression of the battery, the insulating resin exposed in the sheared surface extends, and is exposed in the sheared surface by the insulating resin. Part of the metal conductor layer is covered. It is believed that this substantially reduces the cross-sectional area of the exposed conductor portion in the shear plane. Further, when the nail penetrates in the thickness direction of the current collector, the insulating resin constituting the insulating resin layer extends in the thickness direction at a portion in contact with the nail as the nail moves. Thus, it is considered that the insulating resin is interposed between the nail and the hole of the metal conductor layer formed by the penetration of the nail, and the contact area between the nail and the metal conductor layer is reduced. For this reason, in the lithium secondary battery of the present invention, even if the current collector is sheared due to the compression of the battery, or even if the cathode is short-circuited due to the stimulus of a nail, etc. It is considered that the short-circuit current at this time is reduced.

 As described above, the lithium secondary battery of the present invention is devised so that the separator is broken by the compression of the battery or the short-circuit current between the positive electrode and the negative electrode due to nail penetration or the like is reduced. The amount of heat generated between the electrodes is reduced, and the temperature rise inside the battery is suppressed. As a result, thermal runaway (ignition and burning) of the lithium secondary battery is properly avoided.

 In addition to the effects described above, in the present invention, by setting the thickness of the metal conductor layer to 2.5 m or more, it is possible to prevent the electric resistance of the metal conductor layer from becoming unduly large, and It also has the advantage that the charge and discharge capacity of the battery can be sufficiently ensured.

Here, the upper limit of the thickness of the metal conductor layer is set to 5 / m because the size of the battery is standardized.If the thickness of the metal conductor layer is set too large, the thickness of the insulating resin layer is reduced. This is because the thickness and the thickness of the electrode formed on the current collector must be reduced. The metal conductor layer is made of, for example, aluminum, nickel, copper, or the like. Aluminum is preferably used as the material of the force formed by such techniques as vapor deposition, sputtering, and plating.

 Further, it is preferable that a plurality of through holes penetrating in the thickness direction be formed in the metal conductor layer, and the plurality of through holes are formed, for example, in a grid pattern. With this configuration, even if the current collector is sheared due to, for example, compression of the battery, if the current collector is sheared including the through-hole portion, the metal conductor layer exposed in the shear plane is cut. The area is small. On the other hand, even if the nail is stabbed in the thickness direction of the current collector, the area including the through hole is penetrated, so that the area of the contact horn between the nail and the metal conductor layer is small. In this way, even if the current collector is sheared and nailed and short-circuited between the positive electrode and the negative electrode, the short-circuit current can be reduced by forming the through-hole in the metal conductor layer.

 The insulating needle oil layer is formed of a resin material having high insulation properties, for example, polyimide, polyethylene terephthalate, or silicone rubber. In addition, the thickness of the insulating planting fat layer is set, for example, in a range of 3 to 30 m.

 By the way, lithium secondary batteries can be broadly classified into lithium metal secondary batteries and lithium ion secondary batteries, but the technical idea of the present invention can be applied to any form of lithium secondary batteries. is there.

 In a lithium metal secondary battery, the positive electrode includes, for example, a positive electrode active material capable of absorbing and releasing lithium ions, a conductive agent having a function of supplementing the conductivity of the positive electrode, and a bonding agent for bonding the positive electrode active material and the conductive agent. It is composed as a mixture containing a binder (binder).

 The positive electrode active material is, for example, a polymer conductor such as polyaniline, polyacetylene, poly (p-phenylene), polybenzene, polypyridine, polythiophene, polyfuran, polypyrrol, polyanthracene, polynaphthalene, and derivatives thereof, or Metal oxides such as manganese dioxide, vanadium pentoxide, molybdenum trioxide, chromium trioxide, and cupric oxide; metal sulfides such as molybdenum disulfide, titanium disulfide, and iron disulfide; and inorganic conductive materials such as carbon fluoride Body.

Examples of the conductive agent include acetylene black, graphite, and carbon. Examples of the binder include Teflon resin and an ethylene-propylene-gen terpolymer. Examples of the negative electrode in the lithium metal secondary battery include those using lithium metal and an alloy thereof as a negative electrode active material. These negative electrode active materials constitute the negative electrode in a foil or plate shape.

 Examples of the lithium alloy include an alloy of lithium and at least one metal selected from metals such as aluminum, magnesium, indium, mercury, zinc, force dome, lead, bismuth, tin, and antimony. Specifically, a lithium-aluminum alloy, a lithium tin alloy, a lithium-lead alloy and the like can be mentioned.

As the electrolyte, those generally used in this field, for example, lithium salts and the like can be used. The lithium _{salt, L i PF 6, L i} C 10 4, L i A s F 6, L i BF 4, L i A l C l.,, L i C l or L i B r of any inorganic, salts _{or, CH 3 S0 3 L i,} CF 3 S0 3 L i, L i B (C 6 H 5) 4, or include organic salts such as CF ₃ COOL i. These lithium salts may be used alone or in combination of two or more.

 When the electrolyte is in the form of an electrolytic solution, the electrolyte is used after being dissolved in an organic solvent. Examples of the organic solvent include known solvents (high-dielectric solvents and low-viscosity solvents) generally used in this field.

 Examples of the high dielectric constant solvent include cyclic carbonates having 3 to 5 carbon atoms such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

 Examples of the low-viscosity solvent include chain carbonates having 3 to 9 carbon atoms, chain ethers, esters, and aromatic hydrocarbons.

Examples of the chain carbonate having 3 to 9 carbon atoms include dimethyl carbonate (DMC), getyl carbonate (DEC), dipropyl carbonate (DPC), and methyl ethyl carbonate (MEC). Examples of the ethers include 1,2-dimethoxetane (DME), 1,2-diethoxyethane (DEE), and 1,2-dibutoxetane (DBE). Examples of esters include tetrahydrofuran (THF), Cyclic ethers such as 2-methyltetrahydrofuran (2-Me THF), methyl formate, methyl acetate, Examples of the aromatic hydrocarbon include benzene (Bz), toluene, and xylene.

 The high-dielectric solvent and the low-viscosity solvent may be used alone or in combination of two or more, but when a low-viscosity solvent is used, the low-viscosity solvent is low. It is preferable to use in combination with a high dielectric constant solvent to supplement charge and discharge efficiency. Examples of the combination of a high dielectric constant solvent and a low viscosity solvent include EC—DMC, EC—DEC, PC DMC, PC-DEC, Binary solvent systems such as PC—MEC, ternary solvents such as EC DMC-Bz, EC-DEC_Bz, PC—DMC—Bz, PC D EC—Bz, EC—PC DMC, EC—PC—DEC And four-component solvent systems such as EC-PC-DMC-Bz and EC-PC-DEC-Bz. The ratio between the high dielectric constant solvent and the low viscosity solvent is, for example, 1: 4 to 2: 1 (volume ratio), preferably 1: 2 to 1: 1.

 The electrolyte may be in the form of a solid electrolyte. Examples of the solid electrolyte include polyacrylonitrile, polyvinylidene fluoride, photocurable polymerizable monomers composed of ethoxyethyl glycol acrylate and trimethylolpropane triacrylate, and polyphosphazenes.

On the other hand, when the lithium secondary battery is configured as a lithium ion secondary battery, the positive electrode is configured as, for example, a mixture of a positive electrode active material, a conductive agent, and a binder. , for example, general formula L ip (M0 _{2) q} (Dadashi, M represents cobalt, nickel, and at least one metal of manganese, p, q are integers satisfying the valency) lithium complex represented by and metal _{oxides, L i C o 0 2,} L i N i 0 2, L i Mn 2 0 4, L i Mn 3 0 6 intercalation compound you containing lithium and the like.

 Note that, as the conductive agent and the binder, those similar to those used for the positive electrode of the lithium metal secondary battery can be used.

 The negative electrode of the lithium ion secondary battery is configured as, for example, a mixture of a negative electrode active material, a conductive agent, and a binder.

In this case, a carbon material is preferably used as the negative electrode active material. Examples of this carbon material include graphite, conjugated resins (for example, phenolic resin, acrylic resin, Polyimide resins, polyamide vegetable oils, etc., condensed polycyclic hydrocarbon compounds (eg, naphthalene, phenanthrene, anthracene, etc.), furan resins (eg, furfuryl alcohol, homopolymers of furilal, and copolymers thereof), or Examples include those obtained by firing and carbonizing organic materials such as oxygen crosslinked products of petroleum pitch. These carbon materials may be used alone or in combination of two or more. Graphite is particularly preferably used.

 Note that, as the conductive agent and the binder, those similar to those used for the positive electrode of the lithium metal secondary battery can be used.

 In addition, even in the case of the L-shift of the lithium metal secondary battery and the lithium ion secondary battery, a separator is provided between the positive electrode and the negative electrode in order to retain the electrolyte and prevent a short circuit between the positive electrode and the negative electrode. Is also good. The material of the separator is not particularly limited as long as it is an insulator which is not dissolved in the electrolyte and is easily processed, and examples thereof include porous polypropylene and porous polyethylene.

 Further, as the form of the lithium secondary battery, any of a cylindrical form, a rectangular form, a coin form (button form), and a sheet form can be adopted. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a cross-sectional view showing the structure of a coin-type lithium secondary battery as a typical example to which the present invention can be applied.

 FIG. 2 is an enlarged cross-sectional view of a main part for describing a configuration of a current collector employed in the lithium secondary battery of FIG.

 FIG. 3 is a half sectional view showing the structure of a cylindrical lithium secondary battery as another typical example to which the present invention can be applied.

 FIG. 4 is an enlarged cross-sectional view of a main part for describing a configuration of a laminate (a separator positive electrode body-separator negative electrode body) used to configure the cylindrical lithium secondary battery of FIG.

 FIG. 5 is a diagram for explaining the operation of the positive electrode current collector, taking as an example the laminate employed in the cylindrical lithium secondary battery of FIG.

Figure 6 shows the stack used in the cylindrical lithium secondary battery of Figure 3 as ^. FIG. 4 is a diagram for explaining the operation of a positive electrode current collector.

 Figure 7 is a graph showing the relationship between the thickness of the metal conductor layer of the current collector and the discharge capacity of the battery when the load is 2 C, and the relationship between the thickness of the metal conductor layer and the electrical resistance of the current collector. It is.

 FIG. 8 is a diagram illustrating a state in which the battery is compressed with a round bar.

 FIG. 9 is a diagram illustrating a state where the battery is nailed. BEST MODE FOR CARRYING OUT THE INVENTION

 Hereinafter, two preferred embodiments of the present invention will be described with reference to FIGS. 1 and 2 are diagrams of a coin-type lithium secondary battery, and FIGS. 3 and 4 are diagrams of a cylindrical lithium secondary battery. FIGS. 5 and 6 are diagrams for explaining the operation of the positive electrode current collector, taking as an example the laminate employed in the cylindrical lithium secondary battery.

 The coin-type lithium secondary battery X shown in FIG. 1 has a positive electrode body 1, a negative electrode body 2, and a separator made of, for example, a porous film made of polypropylene interposed between the positive electrode body 1 and the negative electrode body 2. Evening 3 is provided.

Positive electrode 1, for example, L i C o 0 ₂ positive electrode 1 0 for the (lithium cobalt oxide) as an active material is configured to have been formed on the positive electrode current collector 1 1.

 As shown in FIG. 2, the positive electrode current collector 11 has a configuration in which metal conductor layers 13 are formed on both surfaces of an insulating resin layer 12 so as to be electrically connected to each other. A plurality of through holes 14 are formed in the metal conductor layer 13, and the through holes 14 are formed, for example, in a grid pattern. The insulating resin layer 12 is formed to have a thickness of 3 to 3 using, for example, polyimide resin, and the metal conductor layer 13 is formed to have a thickness of 2.5 to 5 μm using, for example, aluminum. The positive electrode current collector 11 thus configured is fixed to the inner surface of a positive electrode can 5 made of, for example, stainless steel.

The negative electrode body 2 has a configuration in which, for example, a negative electrode 20 using a lithium foil as an active material is formed on a negative electrode current collector 21. The negative electrode current collector 21 is fixed to the inner surface of a negative electrode can 7 made of, for example, stainless steel. In the space formed between the positive electrode can 5 and the negative electrode can 7, for example, LiPF ₆ (lithium hexafluorophosphate) is mixed with ethylene carbonate (EC) and dimethyl carbonate (DMC). A non-aqueous electrolyte prepared by dissolving in a solvent is filled. Then, the space between the positive electrode can 5 and the negative electrode can 7 is sealed with, for example, a packing 8 made of polypropylene to complete the battery.

 On the other hand, the cylindrical lithium secondary battery X 'shown in Fig. 3 has the separator 3' as shown in Fig. 4, the positive electrode, the separator 3, and the negative electrode 2 'stacked in this order. In addition, it has a laminate 9 'which is elongated in a belt shape as a whole. The laminated body 9 'is wound around a center pin 90' as shown in FIG. 3, and is accommodated in a cylindrical negative electrode can made of, for example, stainless steel, and the laminated body 9 ' The battery rechargeable battery X 'is roughly configured.

As shown in FIG. 4, the positive electrode body 、 is formed on both sides of the positive electrode current collector 1 さ れ having the same configuration as the positive electrode current collector 11 used in the coin-type lithium secondary battery X (see FIG. 2). a, L i C o 0 ₂ positive electrode 1 to the (lithium cobalt oxide) as an active material 0 'is configured such that made form.

 The negative electrode body 2 ′ is configured such that, for example, a copper foil as the negative electrode current collector 21 ′ is sandwiched from both sides by a negative electrode 20 ′ made of lithium foil.

 As the separator 3 ', for example, a separator made of a porous film made of polypropylene can be used as in separator 3 of the coin-type lithium secondary battery X (see FIG. 1).

 Further, as shown in FIG. 3, the negative electrode body 2 ′ has a negative electrode lead tab 25 ′, and the negative electrode lead tab 25 ′ extends beyond the lower insulating plate 26 ′ to form a negative electrode can 7 ′. Contacting the inner bottom surface. On the other hand, the positive electrode body 導 通 is electrically connected to the positive electrode lead tab 15 ′, and the positive electrode lead tab 15 ′ extends through the upper insulating plate 16 ′ and passes through the positive electrode lead bin 17 ′. Conducted to the positive electrode lid 5 '.

In the space formed between the positive electrode lid 5 'and the negative electrode can 7', for example L i PF ₆ and (lithium hexafluorophosphate) of ethylene carbonate (EC) and Jimechiruka Ichibo sulfonate (DMC) A non-aqueous electrolyte prepared by dissolving in a mixed organic solvent is filled. Then, the space between the positive electrode lid 5 'and the negative electrode can 7' is made of, for example, polypropylene. The battery is completed by sealing with a packing 8 '.

 Both the coin-type lithium secondary battery X and the cylindrical lithium secondary battery X 'described above employ the positive electrode current collectors 11, 1Γ described with reference to FIG. 2 or FIG. There are features where you are. In the lithium secondary batteries X, X 'employing the positive current collectors 11, 1, Γ having such a configuration, the batteries X, X' are compressed and the positive current collectors 11, 1, Γ are broken, or Even if the positive electrodes 1 and Γ and the negative electrodes 2 and 2 'are short-circuited due to nails, the amount of short-circuit current between the positive electrodes 1 and Γ and the negative electrodes 2 and 2' is small, resulting in thermal runaway. Is properly avoided.

 The first reason is that the thickness (cross-sectional area) of the metal conductor layers 13, 13 '(conductor portion) in the positive electrode current collectors 11, 1Γ is reduced, and second, the metal conductor layers 13c 13 It is considered that a plurality of through holes 14 and 1 ′ are formed in the positive electrode current collector 11, and the third reason is that the positive electrode current collector 11 ′ has the insulating resin layer 12.

 These reasons will be specifically described below with reference to the stacked body 9 'of the cylindrical lithium secondary battery X' shown in FIG. 3 as an example.

 First, if the cross-sectional area of the conductor portion of the positive electrode current collector 1 さ れ is reduced, the lithium secondary battery X 'is compressed and the positive electrode current collector 1 破 is broken as shown in FIG. In addition, even if the positive electrode body Γ and the negative electrode body 2 ′ are in direct contact with each other and short-circuited, the conduction area between the positive electrode body 負極 and the negative electrode body 2 ′ also becomes small. Accordingly, it is considered that the current flowing between the positive electrode body Γ and the negative electrode body 2 'does not become so large.

 On the other hand, as shown in FIG. 6, even when the nail K is pierced into the laminated body 9 ′ and the positive electrode body Γ and the negative electrode body 2 ′ are short-circuited via the nail K which is a conductor, if the thickness of the conductor is small, However, it is considered that the contact area between the nail and the conductor of the positive electrode body 1 'is small, and the short-circuit current between the positive electrode body 1 and the negative electrode body 2' is not so large.

Second, if a plurality of through holes 14 'penetrating in the thickness direction of the metal conductor layer 13' are formed, the lithium secondary battery X 'is compressed as shown in FIG. Even if the body 1 剪 is sheared, if the positive electrode current collector 1 含 ん is sheared including the portion of the through-hole 14 ′, the cross-sectional area of the metal conductor layer 13 ′ exposed in the shear plane, Is smaller than the case where no is formed. On the other hand, as shown in FIG. 6, even if the nail K is pierced in the thickness direction of the positive electrode current collector 1 When the area including 14 'is nailed, the contact area between the nail K and the metal conductor layer 13' is reduced. For this reason, even if the positive electrode current collector 1 剪 is sheared and nailed and short-circuited between the positive electrode body Γ and the negative electrode body 2 ′, a through hole 14 ′ is formed in the metal conductor layer 13 ′. By doing so, the short-circuit current is reduced.

 Third, if the positive electrode current collector 1 有 す る is configured to have the insulating resin layer 12, for example, if the positive electrode current collector 1 剪 is sheared by compression of the battery X ′, It is considered that the exposed insulating resin extends, and this insulating resin covers a part of the metal conductor layer 13 ′ exposed in the shear plane. On the other hand, when the nail Κ penetrates in the thickness direction of the positive electrode current collector 1 、, as the nail 移動 moves, the insulating resin constituting the insulating resin layer 12 extends in the thickness direction at the portion in contact with the nail Κ. . As a result, when the insulating resin is interposed between the nail Κ and the hole of the metal conductor layer 13 ′ formed by the penetration of the nail Κ, the contact area between the nail Κ and the metal conductor layer 13 ′ is reduced. Conceivable. For this reason, in the lithium secondary battery X 'of the present invention, the positive electrode current collector 1 に よ る is sheared due to the compression of the battery, or the nail Κ is pierced and the gap between the positive electrode body 負極 and the negative electrode body 2 っ て is formed. It is considered that the short-circuit current at this time is reduced even if the short circuit occurs.

 In addition to the effects described above, in the lithium secondary batteries X and X 'of the present invention, the thickness of the metal conductor layers 13 and 13' of the positive electrode current collectors 11 and 11 'is set to 2.5 m or more. This has the advantage that the electrical resistance of the metal conductor layers 13, 13 'can be prevented from becoming unduly large, and that the charge / discharge capacity can be sufficiently ensured.

 In addition, since the upper limit of the thickness of the metal conductor layers 13, 13 'is 5 / m, even if the size of the battery is standardized, the insulating resin layer of the positive electrode current collector 11, 1Γ The thickness of 12, 12 'and the thickness of the positive electrodes 10, 10' formed on the positive electrode current collector 11, 1 'are not unduly reduced.

 Next, examples of the present invention will be described together with comparative examples to clarify the advantages of the lithium secondary battery of the present invention.

 [Example 1]

In this embodiment, a separator, a positive electrode body, a separator, and a negative electrode body are sequentially laminated to form a laminate having the same configuration as that shown in FIG. The AA size cylindrical lithium secondary battery having the configuration shown in Fig. 3 was fabricated by housing it in a cylindrical negative electrode can and sealing it with the positive electrode lid. For this lithium secondary battery, the discharge capacity was measured, a compression test and a nail penetration test were performed, and the resistance value of the positive electrode current collector constituting the positive electrode body was measured. The results are shown in Tables 1, 2 and 7.

 (Positive electrode body)

 The positive electrode body had a configuration in which positive electrodes were formed on both sides of a positive electrode current collector.

 The positive electrode current collector is made of a 20 / m thick polyimide resin as an insulating resin layer. Was formed by evaporation. However, no through hole was formed.

The positive electrode, L i C o 0 ₂ (lithium Kobanoreto acid) 9 0 wt% as the positive electrode active material, as a conductive agent of acetylene black 2. 5 wt% and graph eye preparative 2. 5 wt%, as a binder (binder) A mixture of 51% of polyvinylidene fluoride resin (PVDF) uniformly mixed was coated and rolled on both sides of the positive electrode current collector.

 (Negative electrode body)

 The negative electrode body was configured such that a copper foil as a negative electrode current collector was sandwiched from both sides by a lithium foil (100 μμηη) as a negative electrode active material.

 (Separate evening)

 For the separation, a polypropylene porous film with a thickness of 25 m was used.

 (Electrolyte)

As an electrolytic solution, 1 L i PF ₆ (the six Furuororin lithium acid) ethylene carbonate sulfonate (EC) and dimethyl carbonate (DMC): was obtained by dissolving 1 molar ratio of the 2 mixed solvent.

 (Measurement of discharge capacity)

After the voltage value was 4. fully charged lithium batteries until 2 V, a discharge current density as 1. O mA / cm ^2, to discharge the lithium battery under constant load, voltage values of the battery 3. The capacity when the voltage became 0 V was defined as the discharge capacity. The discharge capacity is 0.2 C (1 C is equivalent to 0.8 mA), 0.5 C, 1.0 C, and 2.0 Each was measured for the case of c.

 (Measurement of resistance value)

 The resistance between the end of the positive electrode current collector and a portion 27 cm from this end was measured, and this was evaluated as the resistance of the positive electrode current collector.

 (Compression test)

 After fully charging the lithium battery with the above configuration until the voltage value becomes 4.2 V, as shown in Fig. 8, the center of the battery is 65% of the battery diameter with a round bar of 7.9 mm diameter. The battery was compressed to check whether the battery ignited, and the battery temperature was measured. The compression speed was 1 Omm / sec.

 (Nail penetration test)

 After fully charging the lithium battery until the voltage reaches 4.2 V, penetrate the center of the battery with a 2.5 mm diameter nail as shown in Fig. 9 and check for battery ignition, The battery temperature was measured. The nail penetration speed was 1 Om mZ second. [Example 2]

 In this example, the procedure was the same as in Example 1, except that the thickness of the metal conductor layer in the positive electrode current collector was changed to 5 m. The results are shown in Table 1, Table 2 and FIG.

 [Comparative Example 1]

 This comparative example was the same as Example 1 except that the thickness of the metal conductor layer in the positive electrode current collector was 1 m. The results are shown in Table 1, Table 2 and FIG.

 [Comparative Example 2]

 This comparative example was the same as Example 1 except that a 20 / m aluminum foil was used as the positive electrode current collector. The results are shown in Table 1, Table 2 and FIG. [Reference example]

In this reference example, a so-called A1 expand was used in which a plurality of through-holes having a diameter of 2.5 mm were formed in a grid pattern on a 100-m-thick aluminum foil as a positive electrode current collector. Other than the above, the resistance value of the positive electrode current collector and the discharge capacity of the battery when the load was 2 C were measured, respectively. The results are shown in Table 1, and in FIG. 7, the discharge capacity is shown by a one-dot chain line, and the resistance value is shown by a two-dot chain line. [Examples 3 to 8, Comparative Examples 3 to 5]

 Various positive electrode current collectors having different thicknesses of the metal conductor layers were formed, the electric resistance at a point of 27 cm was measured, and the lithium current was measured in the same manner as in Example 1 for each positive electrode current collector. The secondary batteries were formed, and the discharge capacity when the load was 2 C was measured.

 The thickness of the metal conductor layer in Example 3 was 2 m, Example 4 was 2.1 / m, Example 5 was 2.5 m, Example 6 was 3.5 m, Example 7 was 4 m, Example 8 was 4.5 m, Comparative Example 3 was 1.3 / m, Comparative Example 4 was 1.5 m, and Comparative Example 5 was 1.8 μm.

The measurement results of the resistance values and the discharge capacities of these Examples and Comparative Examples were graphed together with Examples 1, Example 2, Comparative Example 1, and Comparative Example 2 as shown in FIG. I plotted. The discharge capacity is indicated by a black diamond, and the resistance value is indicated by a white diamond.

table

 Note: PI indicates polyimide resin.

 The discharge capacity is the capacity when the battery is discharged from a fully charged state (voltage value is 4.2 V) and the voltage value reaches 3.0 V.

The resistance was measured between the end of the positive electrode current collector and a point at a distance of 27 cm from the end.

Table 2

Note: PI indicates polyimide resin. As is clear from Table 1, the battery of Comparative Example 1 has a small discharge capacity at a load of 2 C and a large positive electrode current collector resistance, and is not practical. On the other hand, in the batteries of Examples 1 and 2, the discharge capacity when the load was 2 C was about the same as that of the A1 expand having a thickness of 100 m shown as the reference example. The resistance value of the positive electrode current collector adopted is about the same as that of the A1 expand of the reference example, that is, the batteries of Examples 1 and 2 have an A1 expandable which can withstand practical use as the positive electrode current collector. It has the same level of performance as the battery used and can withstand practical use. As is clear from Table 2, the battery of Comparative Example 2 provided with a positive electrode current collector formed of A1 foil Ignited in both the compression test and the nail penetration test, and the battery temperature was more than 500 ° C. In contrast, the batteries of Examples 1 and 2 did not ignite in each test, and the battery temperature was in the range of 40 to 60 ° C. I Therefore, the batteries of Examples 1 and 2 were used when the inside of the battery (separator ゃ positive electrode current collector) was sheared due to compression or the separator was not maintained in an appropriate state due to nail penetration, resulting in a short circuit between the positive electrode and the negative electrode. Even so, safety is sufficiently ensured.

Further, as apparent from FIG. 7, in the batteries (Examples 1 to 8) in which the thickness of the metal conductor layer in the positive electrode current collector was 2 _C 5 m or more, the discharge capacity of the battery and the resistance value of the positive electrode current collector However, the results are comparable to or better than the A1 expand of the reference example, and are considered to be sufficiently practical.

 As described above, according to the present invention, thermal runaway can be appropriately performed even when the inside of the battery (separator or the positive electrode current collector) is compressed and the positive electrode and the negative electrode are short-circuited due to nail penetration. It is possible to provide a lithium secondary battery capable of ensuring sufficient safety by suppressing the above and further ensuring a high discharge capacity.

Claims

Scope of word blue 1. A lithium secondary battery including: a positive electrode capable of charging and discharging lithium ions; a negative electrode made of a material capable of doping and removing lithium ions, lithium metal or lithium alloy; and an electrolyte permitting lithium ions to move. And  At least one of the positive electrode and the negative electrode is formed on a current collector in which a metal conductor layer is formed on a surface of an insulating resin layer; and  A lithium secondary battery, wherein the thickness of the metal conductor layer is 2.5 to 5 // m.  2. The lithium secondary battery according to claim 1, wherein the current collector has at least a plurality of through holes penetrating in a thickness direction of the metal conductor layer.  3. The lithium secondary battery according to claim 1, wherein the thickness of the insulating resin layer is 3 to 30 / m.  4. The lithium secondary battery according to claim 1, wherein the metal conductor layer is aluminum.  5. The lithium secondary battery according to claim 1, wherein the insulating resin layer is made of polyimide, polyethylene terephthalate, or silicone rubber.  6. A lithium ion including: a positive electrode capable of charging and discharging lithium ions; a negative electrode made of a material capable of doping and removing lithium ions; lithium metal or a lithium alloy; and an electrolyte permitting lithium ions to move. Next battery  At least the positive electrode is formed on a current collector in which an aluminum metal conductor layer is formed on the surface of an insulating resin layer; and  A lithium secondary battery, wherein the thickness of the metal conductor layer is 2.5 to 5 m, and the thickness of the insulating resin layer is 3 to 30 m.  7. The lithium secondary battery according to claim 6, wherein the current collector has at least a plurality of through holes penetrating in a thickness direction of the metal conductor layer.