JP2012043629A - Separator for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a safe nonaqueous electrolyte secondary battery preventing a short circuit and an explosion even in a state of overcharge in which a voltage of several tens of volts is applied.SOLUTION: The separator for the nonaqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of charging and discharging lithium, a separator, and a nonaqueous electrolyte containing an electrolyte dissolved in a nonaqueous solvent contains a conductive layer. The apparent volume resistivity of the conductive layer is in the range of 1×10to 1×10Ω cm, and the melting point of the separator is 170°C or higher.

Description

  The present invention provides a non-aqueous electrolyte secondary battery separator that can realize a safe non-aqueous electrolyte secondary battery even under overcharge, and a non-aqueous electrolysis using the non-aqueous electrolyte secondary battery separator. The present invention relates to a liquid secondary battery.

A lithium secondary battery has a positive electrode in which an active material layer containing a positive electrode active material such as a lithium compound typified by lithium cobaltate is formed on a current collector, and occlusion / release of lithium typified by graphite. Non-aqueous electrolysis in which an active material layer containing a negative electrode active material such as a carbon material is formed on a current collector and an electrolyte such as a lithium salt such as LiPF ₆ is dissolved in an aprotic non-aqueous solvent It is composed of a liquid and a separator made of a polymer porous membrane, and is characterized by being lightweight while having a high energy density.

  Taking advantage of this feature, lithium secondary batteries have come to be used in a wide range of fields such as mobile phones, notebook personal computers, electric tools, etc., as electric products have become lighter and smaller in recent years. In particular, against the backdrop of the recent growing global interest in global warming, the automobile industry has been expected to reduce carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Development of high-capacity, high-power lithium secondary batteries that are key devices is actively underway.

  Since the lithium secondary battery for EV or HEV requires a high voltage of several hundred volts for driving the motor, a large number of single cells are connected in series to produce a necessary high voltage. At this time, for the convenience of assembly and management, a module battery is usually constructed by connecting several to 10 single cells in series, and a plurality of module batteries are combined to form an overall battery system. Is building. Since battery input / output control is normally performed in module battery units, a voltage of several tens of volts is applied to the module battery. However, if there are defective cells in the module battery, Is assumed to be a situation from an extreme overcharged state in which a voltage of several tens of volts of the entire module battery is applied to one single cell, to an internal short circuit, thermal runaway, and thermal runaway to other normal batteries. . The same situation also occurs when a battery is mistaken when connecting a plurality of batteries in series, when a battery malfunctions, or when a battery is damaged due to a traffic accident. The most effective way to prevent this situation is to individually monitor and control a single cell, but it is not a practical method due to the complexity and cost of control, and it is resistant to overcharged conditions. There is a strong demand for such a material system.

  As a countermeasure against the overcharged state, as shown in Patent Document 1, a method of adding an overcharge preventing agent to the electrolytic solution has been conventionally used. In these methods, a compound having an oxidation potential equal to or higher than the upper limit voltage value of the battery is added to the electrolyte as an overcharge inhibitor, and when the overcharged state is reached, the compound is oxidized and polymerized to increase the active material surface. In this method, the overcharge current is suppressed by forming a resistance film to stop the progress of overcharge, or the charge is stopped by detecting changes in internal pressure and temperature due to gas or heat generated by the polymerization reaction. However, many of the compounds used as overcharge inhibitors are electrochemically and chemically active substances for that purpose, and when added in large amounts in the electrolyte, they may react even under normal battery usage conditions. This causes an increase in battery resistance and a decrease in capacity. On the other hand, if the amount of addition is reduced, in a lithium secondary battery for EV or HEV in which a large current flows, the amount of current that can be consumed during overcharging becomes small, making it difficult to achieve a sufficient effect.

  In addition, the charging upper limit voltage of a battery for portable devices is usually about 4V to 16V, whereas the charging upper limit voltage of a battery module for EV or HEV is 20V to several hundreds V, as described above. When an excessive overcharged state is reached due to the inclusion of a defective battery, the reaction proceeds rapidly, and the film with the overcharge inhibitor is easily decomposed, so it is difficult to ensure safety with the overcharge inhibitor alone. is there.

  On the other hand, apart from measures against overcharging of the battery, attempts have been made to prevent the short circuit of the battery by imparting conductivity to the separator. Examples of such techniques include Patent Documents 2 to 5. Patent Documents 6 and 7 disclose techniques for improving cycle characteristics by imparting conductivity to a separator. Patent Document 8 discloses a technique for preventing winding slippage by applying an acrylic pressure-sensitive adhesive material in which graphite or the like is dispersed to a separator so as to improve adhesion with an electrode. Patent Document 9 discloses a technique for improving safety by applying metal particles to a separator and adsorbing a gas generated by overcharging.

  In Patent Document 2, an antistatic agent is mixed or applied or sprayed on the separator surface to make the separator antistatic and prevent the adhesion of conductive fine particles such as active materials in the battery manufacturing process due to static electricity. Thus, a technique for preventing a short circuit due to penetration of fine particles is disclosed. However, antistatic agents are generally used to prevent charge by using ions that adsorb and liberate moisture in the air, and are basically effective in non-aqueous electrolyte secondary batteries that exclude moisture. It was impossible. That is, even if the separator obtained by this method is used for a non-aqueous electrolyte secondary battery, it does not function as a separator having conductivity on the surface.

  Patent Document 3 discloses a technique for improving irreversible characteristics by forming an alkali metal powder layer made of Li, Na, or K on the separator surface. However, as is well known, an alkali metal is a highly reactive metal and easily reacts with oxygen and moisture in the air, so forming such a metal powder layer on the separator surface is a big problem for safety. There is. Even in Patent Document 3, a problem regarding safety is pointed out, and as a means for solving the problem, an alkali metal polymer coating or the like is mentioned, but if the polymer coating is performed, the conductivity of the metal is inhibited, A conductive separator cannot be formed on the surface.

  Patent Document 4 discloses a separator formed by stretching a resin composition containing a thermoplastic resin and a conductive filler. However, the technique disclosed in Patent Document 4 is generally used under the condition of using a battery. The separator is non-conductive because the distance between the conductive fillers in the separator is sufficiently large, and when there is an abnormality such as an internal short circuit, the separator thermally contracts and the conductive fillers contact each other to form a conductive path (shutdown) (Effect), the remaining capacity of the battery is quickly discharged to make it safe. That is, the separator of Patent Document 4 does not have conductivity as a whole as well as the surface when a normal battery is used.

  Patent Document 5 discloses a multilayer porous membrane having an electrically conductive layer containing conductive particles and an electrically insulating layer containing non-conductive particles as one method for increasing the thermal conductivity in the thickness direction of the separator. It is disclosed. However, in order to increase the thermal conductivity of the separator, these particles need to form a percolation with each other. For this reason, Patent Document 5 describes the necessity of adding a large amount of filler. A polymer film containing a large amount generally tends to be fragile due to a decrease in flexibility. On the other hand, as is well known, the active material of a non-aqueous electrolyte secondary battery, in particular, the negative electrode active material expands in volume due to occlusion of lithium, and thus a large pressure is applied to the separator. In particular, since the volume expansion of the active material is further promoted in the overcharged state, and a pressure higher than that in the normal battery use state is applied to the separator, the strength brittle separator disclosed in Patent Document 5 is in the overcharged state. There is a problem that the possibility of causing an internal short circuit is high. In order to prevent a short circuit due to volume expansion of the active material in an overcharged state, usually a puncture strength of at least 250 g is required, preferably 300 g or more, more preferably 350 g or more. Patent Document 5 states that the thickness of the electrically conductive layer is preferably 2/3 or more of the entire separator, but if the thickness of the electrically conductive layer is thick, it may function as a current collector, and a large charge / discharge current flows on the separator surface. There is a problem that the heat deterioration of the separator is accelerated by the Joule heat generation.

  In Patent Document 6, the separator surface has conductivity, and the conductive layer on the separator surface acts as a positive electrode conductor (current collector) when the conductivity performance of the positive electrode conductor (current collector) deteriorates. Discloses a separator having a function of extending the cycle life of the battery. However, as disclosed in Patent Document 6, the fact that the conductive layer on the separator surface acts as a positive electrode conductor (current collector) means that a large charge / discharge current flows on the separator surface even under normal battery usage conditions. There is a problem that the thermal degradation of the separator proceeds due to the Joule heat generation.

  In Patent Document 7, the active material is applied onto the conductive film provided on the separator surface and the separator and the electrode are integrated, so that the electrode is thinned and the opposing area between the electrodes is widened, thereby reducing the current density. Thus, a technique for improving the cycle life by suppressing the consumption rate of the negative electrode is disclosed. However, as disclosed in Patent Document 7, when a conductive film is formed on one surface of a separator and a paste mainly composed of an active material is applied thereon as a current collector, the solvent of the paste penetrates the separator. Therefore, there is a problem that the binder resin dissolved in the solvent also penetrates into the separator and closes the fine pores of the separator to deteriorate the battery performance. Further, when a non-woven fabric or a woven fabric is used as the substrate instead of the microporous film, there is a risk that the active material penetrates the substrate and penetrates in the thickness direction. In addition, since the conductive film acts as a current collector, a large charge / discharge current flows on the separator surface, and there is a problem that the thermal degradation of the separator proceeds due to the Joule heat generation. In addition, as described in Non-Patent Document 1, a normal electrode is applied and dried and then compressed by a roll press to make the thickness uniform, smooth the surface, and prevent peeling from the current collector. In the integrated separator and electrode disclosed, it is difficult to perform pressing because there is a risk of deformation of the separator, crushing of fine holes, or breakage of the separator by an active material. There is a problem that the yield is lowered as described in. Furthermore, the lithium transition metal composite oxide used as the positive electrode active material has high electrical resistance. Therefore, when the positive electrode is formed only with this lithium transition metal composite oxide, the conductivity is insufficient. Therefore, when the lithium transition metal composite oxide is used as the positive electrode active material, acetylene black, carbon black, natural graphite In addition, the conductivity is ensured by adding a conductive agent such as fine particles of artificial graphite, but when the pressing is not performed, there is a problem that the conductive path is not sufficiently formed and the battery performance is lowered.

  Patent Document 8 discloses a technique for preventing winding slippage by applying graphite or an acrylic pressure-sensitive adhesive in which graphite is dispersed on the separator surface to enhance the adhesion between the separator and the electrode. However, in order to develop sufficient adhesive strength, the thickness of the adhesive layer needs to be 5 μm or more, and like other patent documents, the adhesive layer functions as a current collector to greatly increase the separator surface. There is a problem that the discharge current flows and the thermal deterioration of the separator proceeds. Further, if the thickness of the adhesive layer is 5 μm or more, it may be a factor that impairs air permeability.

  In Patent Document 9, oxygen is generated in an overcharged state by using a separator whose surface is opposite to the positive electrode and coated with Ti, Al, Sn, Bi, Cu, Si, Ga, W, Zr, B, Mo, or the like. A technique for suppressing ignition and explosion by absorbing gas is disclosed. However, in order to sufficiently absorb the oxygen gas generated from the positive electrode, it is necessary to coat with the same amount of metal as the positive electrode active material, and since the metal oxidation reaction is generally an exothermic reaction, There is a problem that the risk of meltdown and the like is high. In Patent Document 9, this problem is avoided by taking a relatively low charging speed of 1.5 to 2.5 C, but it cannot sufficiently cope with a higher discharging speed. . In the technology disclosed in Patent Document 9, when the safety is taken into consideration, the thickness of the metal coating layer is important as described above, but there is no description about these, and the safety improvement of the battery is insufficient.

JP 2003-297423 A Japanese Patent Laid-Open No. 10-154499 JP 2005-317551 A Japanese Patent No. 4145087 JP 2006-269358 A JP 2008-84866 A Japanese Patent Laid-Open No. 5-21069 Japanese Patent Laid-Open No. 11-213980 Japanese Patent Laid-Open No. 11-16666

Lithium-ion secondary battery (2nd edition) published by Nikkan Kogyo Shimbun, January 27, 2000, page 174 Latest heat-resistant polymer Published by Technical Center, Inc., 1st May, 1987, from the first row to the fourth row on the right column of page 6. Latest lithium-ion secondary battery Published by Information Technology Corporation, February 29, 2008, page 65, line 7 to line 8

  The present invention has been made in view of the above-described conventional situation, in which defective cells are mixed in a module battery, and a voltage of several tens of volts of the entire module battery is applied to one or a few single cells. Separator for non-aqueous electrolyte secondary battery that realizes highly safe non-aqueous electrolyte secondary battery that can prevent short circuit and explosion even if it reaches overcharged condition, and for this non-aqueous electrolyte secondary battery An object is to provide a non-aqueous electrolyte secondary battery using a separator.

  As a result of earnest research to solve the above problems, the present inventors have found that the separator can be provided with a conductive layer, and that the meltdown temperature of the separator can be set to 170 ° C. or more, whereby the overcharge resistance can be significantly improved. The present invention has been completed.

That is, the gist of the present invention is as follows.
In a separator for use in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, The separator has a conductive layer, and the apparent volume resistivity of the conductive layer is 1 × 10 ^−4.
A Omega · cm to 1 × 10 ⁶ Ω · cm, the non-aqueous electrolyte secondary battery separator, wherein the meltdown temperature of the separator is 170 ° C. or higher, consists in.

Another gist of the present invention is as follows.
In a separator for use in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, The separator has a conductive layer, the volume resistivity of the conductive layer is 1 × 10 ⁻⁶ Ω · cm to 1 × 10 ⁶ Ω · cm, and the meltdown temperature of the separator is 170 ° C. or higher. And non-aqueous electrolyte secondary battery separator.

Another gist of the present invention is as follows.
In a separator for use in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, The separator has a conductive layer, the surface electrical resistance of the conductive layer is 1 × 10 ⁻² Ω to 1 × 10 ⁹ Ω, and the meltdown temperature of the separator is 170 ° C. or higher. It exists in the separator for electrolyte solution secondary batteries.

Another gist of the present invention is as follows.
In a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, the separator includes the book The present invention resides in a non-aqueous electrolyte secondary battery, which is a separator for a non-aqueous electrolyte secondary battery of the invention.

Another gist of the present invention is as follows.
The present invention resides in a non-aqueous electrolyte secondary battery module in which five or more non-aqueous electrolyte secondary batteries are connected in series and requires a voltage of 20 V or more for full charge.

  According to the present invention, since the separator has a conductive layer and the meltdown temperature is 170 ° C. or higher, defective cells are mixed in the module battery, and one to a small number of single cells dozens of the entire module battery. Provided is a highly safe non-aqueous electrolyte secondary battery that can prevent a short circuit and an explosion even when an overcharged state in which a voltage of V is applied.

  Details of the reason why the overcharge resistance for a non-aqueous electrolyte secondary battery can be greatly improved by providing a conductive layer on the separator for a non-aqueous electrolyte secondary battery and having a melt-down temperature of the separator of 170 ° C. or higher. Although it is unknown, it is presumed that the effect of the conductive layer provided on the surface of the separator or in the middle is due to some influence on the electric field inside the battery in the overcharged state. Further, the meltdown temperature of the separator is considered to be basically determined by the melting point of the material constituting the base material. However, when the base material is a resin, as described in Non-Patent Document 2, for example, an amorphous resin is used. If the temperature is 20 to 30 ° C. lower than the glass transition temperature, and if it is a crystalline resin, the temperature range up to several tens of degrees below the melting point is practically usable, and the resin starts to soften at a temperature higher than that. There are many. Therefore, when the meltdown temperature is less than 170 ° C., it is considered that the base resin constituting the separator often starts to soften at a temperature of approximately 150 ° C. or less. When the softening of the resin starts, it is considered that the thermal contraction or deformation of the separator occurs and the conductive path of the conductive layer formed on the separator surface is likely to break. As a result, it is estimated that the effect of improving the overcharge resistance of the surface conductive layer may be reduced. Although the detailed reason why 150 ° C. is the threshold for overcharge resistance is unknown, as described in Non-Patent Document 3, the non-aqueous electrolyte solution is thermally decomposed at 150 to 160 ° C. or reacted with the positive electrode. Therefore, it is considered that the gas and other by-products generated at that time may have some influence.

  Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is limited to these specific contents. However, various modifications can be made within the scope of the invention.

[Separator for non-aqueous electrolyte secondary battery]
The separator for a non-aqueous electrolyte secondary battery of the present invention is characterized by having a conductive layer, and the apparent volume resistivity of the conductive layer is 1 × 10 ⁻⁴ Ω · cm to 1 × 10 ⁶ Ω · cm. . Alternatively, a conductive layer is provided on at least one surface, and the volume resistivity of the conductive layer is 1 × 10 ⁻⁶ Ω · cm to 1 × 10 ⁶ Ω · cm. Alternatively, the separator has a conductive layer, and the surface electrical resistance of the conductive layer is 1 × 10 ⁻² Ω to 1 × 10 ⁹ Ω.
Furthermore, the meltdown temperature of each of the separators is 170 ° C. or higher.

{Base material}
As the base material of the separator of the present invention, a porous film or a non-woven fabric obtained by a conventionally known method can be appropriately used as long as the meltdown temperature is 170 ° C. or higher. There is no restriction | limiting, It can manufacture by forming a conductive layer in the at least one surface of this base material.
Moreover, even if the meltdown temperature of the substrate is lower than 170 ° C., the meltdown temperature may be 170 ° C. or higher as a whole separator by providing a heat-resistant layer on at least one surface thereof. The heat-resistant layer may be composed of either an organic material such as a resin or an inorganic material such as an inorganic filler, or both may be used in combination.

Specific examples of the method for obtaining the separator substrate of the present invention include the following methods. Moreover, the form of the multilayer which combined two or more of the following methods may be sufficient, and the form of the multilayer which formed the several layer by one method may be sufficient.
(1) A low molecular weight material that is compatible with the polyolefin resin and can be extracted in a later step is added to the polyolefin resin, melt kneaded and formed into a sheet, and the low molecular weight material is extracted after stretching or before stretching. (2) Stretching method in which low-temperature stretching and high-temperature stretching are added to a highly elastic sheet prepared by forming a crystalline resin into a sheet with a high draft ratio, and (3) a thermoplastic resin is inorganic or organic. Interfacial exfoliation method in which filler is added to melt knead and sheet, and the interface between resin and filler is exfoliated by stretching to make it porous (4) Addition of β crystal nucleating agent to polypropylene resin to melt knead and form sheet The β crystal nucleating agent method in which a β crystal-generated sheet is stretched and made porous by utilizing crystal transition (5) Fleece formation methods such as dry method, wet method, spunbond method, melt blown method, and chemical Bond law, support -Nonwoven fabric forming method that combines fiber bonding methods such as the marbond method, needle punch method, and spunlace method as appropriate

{Heat-resistant layer}
An example of a method for imparting a meltdown temperature of 170 ° C. or higher to the separator of the present invention includes a method of forming a heat resistant porous layer on the separator base material obtained by the above-mentioned known method. The heat-resistant porous layer needs to be formed on at least one surface of the base material, the base material may be disposed on both surfaces of the heat-resistant layer, and the heat-resistant layer may be formed on both surfaces of the base material, More preferably, the heat-resistant layer is formed on both surfaces of the substrate.

<Constituent material of heat-resistant layer>
Examples of the material constituting the heat-resistant layer include a heat-resistant inorganic or organic filler, a heat-resistant inorganic or organic fiber, or a heat-resistant resin. These may be used alone, or two or more kinds of materials may be appropriately selected and used.
For example, as an inorganic filler having heat resistance, carbonates such as calcium carbonate, magnesium carbonate and barium carbonate; sulfates such as calcium sulfate, magnesium sulfate and barium sulfate; chlorides such as sodium chloride, calcium chloride and magnesium chloride; In addition to oxides such as aluminum oxide, calcium oxide, magnesium oxide, zinc oxide, titanium oxide, and silica, silicates such as talc, clay, and mica may be used. Among these, from the viewpoint of solvent resistance, oxides such as aluminum oxide, magnesium oxide, and titanium oxide, and sulfates such as magnesium sulfate and barium sulfate are preferable, and aluminum oxide, magnesium oxide, titanium oxide, and barium sulfate are particularly preferable.
Examples of heat-resistant organic fillers include polymethylpentene, polyamide, polyimide, polyamideimide, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polytrimethylene terephthalate, polysulfone, polyphenylene sulfide, polyether ketone, polyether sulfone. Hong, polyetherimide, polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, polychlorotrifluoroethylene, polyvinyl fluoride, ethylene / tetrafluoroethylene copolymer Examples of particles made of heat-resistant resins such as polymers and ethylene / chlorotrifluoroethylene copolymers Door can be. Alternatively, crosslinked resin particles such as a crosslinked methacrylic resin and particles of a high melting point organic material such as benzoguanamine or norbornene oligomer can be used.
Examples of the inorganic fiber having heat resistance include amorphous fibers such as glass fibers, polycrystalline fibers such as alumina fibers, and single crystal fibers such as potassium titanate fibers.
As the organic fiber having heat resistance, cellulose fiber or a fiber made of the above-mentioned heat-resistant resin can be preferably used.
As the heat resistant resin, the aforementioned heat resistant resin can be preferably used. A solvent-soluble resin can form a heat-resistant layer by preparing and applying a resin solution. If the solvent-insoluble resin is a thermoplastic resin, the heat-resistant layer can be formed using a technique such as multilayer molding.

  When the filler is used for the heat-resistant layer, the filler content is usually 60 to 99 parts by weight, preferably 70 to 97 parts by weight, more preferably 80 to 95 parts by weight with respect to 100 parts by weight of the heat-resistant layer. If the filler content in 100 parts by weight of the heat-resistant layer is 60 parts by weight or more, sufficient heat resistance as the heat-resistant layer can be obtained. If the filler content in 100 parts by weight of the heat-resistant layer is less than 99 parts by weight, sufficient strength as the heat-resistant layer can be obtained by the action of the binder, which is the remaining component.

The particle size of the filler used for the heat-resistant layer is usually 0.001 μm to 3 μm, preferably 0.01 μm to 2 μm, more preferably 0.05 μm to 1 μm. The aspect ratio of the filler is usually 1 to 10, preferably 1 to 5, and more preferably 1 to 2.
When the particle size of the filler is 0.001 μm or more, it is possible to form a heat-resistant layer having a uniform structure in which filler aggregation is less likely to occur when the heat-resistant layer is formed. If the particle size of the filler is 3 μm or less, the heat-resistant layer can be thinned, and the heat-resistant layer can be prevented from being reduced in air permeability and, in turn, ion permeability. When the aspect ratio of the filler is 10 or less, the heat-resistant layer can be densely configured.

<Formation method>
The formation method in particular of a heat insulation layer is not restrict | limited, A well-known method is used.
The heat-resistant layer can be easily formed on the substrate by using a known technique such as coating or spraying on a slurry made of inorganic or organic filler, or inorganic or organic fiber, or a heat-resistant resin solution. Examples of methods include forward roll coaters, reverse roll coaters, gravure coaters, knife coaters, blade coaters, rod coaters, air doctor coaters, curtain coaters, fountain coaters, die coaters, kiss coaters, spin coaters, cast coaters, dip coatings. And spray coating.
Alternatively, the heat-resistant layer may be formed using an electrospinning method (electrospinning), or the heat-resistant layer can be formed using a technique such as multilayer molding.

{Conductive layer}
<Conductive material>
The material constituting the conductive layer according to the present invention (hereinafter sometimes referred to as “conductive material”) is not particularly limited as long as it has conductivity, and examples thereof include metals and carbonaceous materials. Can be used.

When the conductive material is a metal, the criteria for selecting a suitable metal material are different between the conductive layer facing the positive electrode and the conductive layer facing the negative electrode when the non-aqueous electrolyte secondary battery is assembled.
That is, when the conductive layer faces the positive electrode, the conductive layer is exposed to a high potential, so gold, platinum, or an alloy thereof having a high oxidation potential is preferably used. Moreover, the valve metal which produces a passive film by anodization can also be used suitably. Examples of the valve metal include aluminum, tungsten, molybdenum, titanium, and tantalum. Further, stainless steel having a chromium oxide film can also be suitably used.

  For the conductive layer facing the negative electrode, it is necessary to select a metal material that does not form an alloy with lithium. Examples of such a metal include copper, nickel, titanium, iron, molybdenum, and chromium, and any of them can be preferably used.

  When the conductive material is a carbonaceous material, there is no particular difference between the conductive layer facing the positive electrode and the conductive layer facing the negative electrode, and amorphous carbon fine particles such as graphite, carbon black and needle coke, or nanocarbon materials such as carbon nanotubes Any of these can be suitably used. The carbonaceous material is not particularly limited by its production method, and any natural graphite or artificial graphite can be suitably used as long as it is graphite. For carbon black, ketjen black, channel black, furnace black are black carbon powders obtained by incomplete combustion of natural gas, acetylene, anthracene, naphthalene, coal tar, aromatic petroleum fractions, etc. Acetylene black, thermal black, lamp black and the like are all preferably used.

  A conductive material may be used individually by 1 type, and 2 or more types may be mixed and used for it.

<Formation method>
A method for forming the conductive layer is not particularly limited, and a known method is used.
As an example, a method of forming a conductive layer on at least one surface of the above-mentioned base material by a method such as sputtering, ion plating, or vacuum deposition may be mentioned. As another example, a slurry in which a conductive material is mixed in a solvent together with a binder is prepared, and this slurry is at least a substrate by a known method such as doctor blade or roll coater, die coater, dipping or spraying. The method of apply | coating to one surface and drying and forming a conductive layer is mentioned. In addition, when the conductive layer is formed inside the separator, a method in which another porous material is laminated and integrated on the separator having the conductive layer formed on one side, or a conductive material is contained in the inner layer in multilayer molding. The method etc. are mentioned.

  When the conductive layer is formed by the above coating method, the solvent, binder, etc. used for the preparation of the slurry can be arbitrarily selected according to the conductive material and the resin constituting the base material, but as an example on the surface of the polyolefin base material In the case where a conductive layer using carbon black as a conductive material is formed by a coating method, as the binder, one or more water-soluble compounds such as polyvinyl alcohol and sodium carboxymethyl cellulose can be used. As water, water is preferably used. Therefore, in this case, the conductive layer is formed by applying a slurry in which carbon black is dispersed in an aqueous polyvinyl alcohol solution or an aqueous solution of sodium carboxymethyl cellulose to the separator surface and drying.

  The solid content concentration of the conductive material in the slurry is usually 1% by weight or more, preferably 3% by weight or more, more preferably 5% by weight or more. Moreover, it is 50 weight% or less normally, Preferably it is 40 weight% or less, More preferably, it is 30 weight% or less. When the solid content concentration of the conductive material is within the above range, uniform and uniform coating is possible, which is preferable.

  Moreover, binder content, such as polyvinyl alcohol in a slurry, is 1 weight part or more normally with respect to 100 weight part of electrically conductive materials, Preferably it is 3 weight part or more, More preferably, it is 5 weight part or more. Further, it is usually 50 parts by weight or less, preferably 35 parts by weight or less, more preferably 20 parts by weight or less. When the content of the binder is in the above range, the conductive layer can have appropriate mechanical strength, air permeability, and conductivity, which is preferable.

<Thickness>
The thickness of the conductive layer (thickness per one surface) is usually 0.001 μm, preferably 0.003 μm or more, more preferably 0.005 μm or more. Moreover, it is 15 micrometers or less normally, Preferably it is 10 micrometers or less, More preferably, it is 5 micrometers or less. When the thickness of the conductive layer is within the above range, the effect of improving the overcharge resistance is more effectively exhibited, which is preferable.

  The conductive layer may be formed on one surface of the separator, may be formed on both surfaces, or may be formed inside as an intermediate layer, but is preferably formed on the surface.

When the conductive layers are formed on both surfaces of the separator, the total thickness of the conductive layers on both surfaces is preferably 15 μm or less, and more preferably 10 μm or less, in order to suppress the thickness of the entire separator. Further, when the conductive layer uses a carbonaceous material, it is preferably 0.002 μm or more, and more preferably 0.01 μm or more.
When the conductive layer is made of a metal material, it is preferably 0.002 μm or more, and more preferably 0.01 μm or more. On the other hand, the upper limit is preferably 1 μm or less, more preferably 0.6 μm or less, and further preferably 0.2 μm or less. In addition, the thickness of a conductive layer is measured by the method as described in the term of the below-mentioned Example.

  When forming the conductive layer on both surfaces of the separator, the thickness of the formed conductive layer and the conductive material used may be different or the same on both surfaces of the separator. Thus, a metal suitable for the negative electrode facing surface side may be used for one surface of the separator, and a metal suitable for the positive electrode facing surface side may be used for the other surface of the separator.

<Surface electrical resistance, surface resistivity, and volume resistivity>
The separator of the present invention has (1) an apparent volume resistivity of 1 × 10 ⁻⁴ Ω · cm to 1 × 10 ^6.
Ω · cm, or (2) volume resistivity is 1 × 10 ⁻⁶ Ω · cm to 1 × 10 ⁶ Ω · cm, or (3) surface electrical resistance is 1 × 10 ⁻² Ω to 1 × 10 ⁹ Ω, It has a conductive layer.
(1) The apparent volume resistivity of the conductive layer is 1 × 10 ⁻⁴ Ω · cm to 1 × 10 ⁶ Ω · cm, preferably 1 × 10 ⁵ Ω · cm or less, more preferably 1 × 10 ⁴ Ω · cm or less.
(2) The volume resistivity of the conductive layer is 1 × 10 ⁻⁶ Ω · cm to 1 × 10 ⁶ Ω · cm, preferably 1 × 10 ⁻³ Ω · cm or more, more preferably 1 × 10 ⁻² Ω · cm or more. The upper limit is preferably 1 × 10 ³ Ω · cm or less, and more preferably 1 × 10 ² Ω · cm or less.

Here, the volume resistivity is a value specific to the material forming the conductive layer. For example, “Chemical Handbook, Basic, Revised 5th Edition, II-611, Table 14.9, published by Maruzen Co., Ltd.” Guided on the 20th of the month. However, for acetylene black, the value of volume resistivity was obtained from the list of physical properties on the homepage of Denki Kagaku Kogyo Co.
Since the conductive layer is porous because it requires a permeation path for ions such as lithium ions, the volume resistivity inherent in the conductive material is affected by the influence of the voids and the contact resistance between the conductive materials. The apparent volume resistivity has a higher value.
If the apparent volume resistivity or volume resistivity of the conductive layer exceeds the above upper limit, details of the reason are unclear, but it is difficult to obtain a sufficient overcharge resistance improving effect according to the present invention. When the apparent volume resistivity or volume resistivity is less than the lower limit, the ventilation resistance due to the conductive layer is increased, and the characteristics of the separator as a lithium ion movement path may be impaired. If the apparent volume resistivity or volume resistivity is less than the lower limit, the conductive layer may function as a current collector, and the separator may be thermally deteriorated due to Joule heat generation.

(3) The surface electrical resistance of the conductive layer is 1 × 10 ⁻² Ω to 1 × 10 ⁹ Ω, preferably 1 × 10 ⁻¹ Ω or more, more preferably 1Ω or more. The upper limit is preferably 1 × 10 ⁸ Ω or less, more preferably 1 × 10 ⁷ Ω or less.
Further, the surface resistivity of the conductive layer is preferably 4 × 10 ⁻² Ω / □ or more, more preferably 1 × 10 ⁻¹ Ω / □ or more, and further preferably 1Ω / □ or more. The upper limit is preferably 1 × 10 ⁹ Ω / □ or less, more preferably 1 × 10 ⁸ Ω / □ or less, and further preferably 1 × 10 ⁷ Ω / □ or less.

  If the surface electrical resistance of the conductive layer is larger than the above upper limit, details of the reason are unclear, but it is difficult to obtain a sufficient overcharge resistance improving effect according to the present invention. If the surface electrical resistance is less than the lower limit, the ventilation resistance by the conductive layer is increased, and the characteristics of the separator as a lithium ion transfer path may be impaired. If the surface electrical resistance is less than the lower limit, the conductive layer may function as a current collector, and the separator may be thermally deteriorated due to Joule heat generation. In addition, the surface electrical resistance, the surface resistivity, and the apparent volume resistivity of the conductive layer are measured by the methods described in the examples described later.

<Features>
As described above, the conductive layer according to the present invention may be formed on at least one surface of the separator, or may be formed as an intermediate layer sandwiched between base materials. And, with respect to the conventional technology for imparting conductivity to the separators as described in Patent Documents 2 to 5, it is clearly distinguished as follows, and has excellent overcharge resistance due to its characteristic configuration. can get.

In the separator using the antistatic agent described in Patent Document 2, as described above, the antistatic agent generally performs antistatic using ions liberated by adsorbing moisture in the air. In a non-aqueous electrolyte secondary battery that excludes moisture, the effect cannot be exhibited.
On the other hand, the conductive layer formed on the separator of the present invention is made of, for example, a metal or a carbonaceous material, and exhibits sufficient conductivity even in the environment of a non-aqueous electrolyte secondary battery from which moisture is excluded. Is.

  In the technique for improving the irreversible characteristics by forming an alkali metal powder layer on the separator surface described in Patent Document 3, as described above, the alkali metal is a highly reactive metal and can easily be combined with oxygen and moisture in the air. In order to react, forming such a metal layer on the separator surface has a big problem on safety, but the conductive layer according to the present invention is not reactive like an alkali metal, and is in a normal environment. It can be handled and has excellent handleability.

As described above, the separator containing a conductive filler in the thermoplastic resin described in Patent Document 4 has no conductivity when the battery is used normally.
Since the conductive layer according to the present invention is present as the surface of the separator or as an intermediate layer, there is no short circuit between the positive and negative electrodes during normal battery use, and sufficient conductivity can be imparted as necessary.

  As described above, the separator described in Patent Document 5 is brittle in strength and has a high possibility of causing an internal short circuit in an overcharged state. However, the conductive layer according to the present invention is formed on the surface or intermediate layer of the separator. Since it exists, it has little or no effect on the strength of the separator, can sufficiently withstand the expansion of the active material during overcharge, and does not cause a problem such as an internal short circuit. Moreover, since the separator described in Patent Document 5 contains a large amount of filler having high thermal conductivity, the thermal conductivity in the thickness direction is 0.5 W / (m · K) or more. The thermal conductivity is about 0.2 W / (m · K).

{Porosity}
The porosity as the degree of porosity of the separator of the present invention is usually 30 to 90%, preferably 35 to 80%, more preferably 38 to 70%. Moreover, it is 90% or less normally, Preferably it is 80% or less, More preferably, it is 70% or less. When the porosity of the separator is within the above range, the battery performance can be sufficiently exhibited, and an internal short circuit is hardly generated, which is preferable.

In addition, the porosity of the separator in this invention is defined by the weight method as follows.
That is, when the separator thickness (total thickness including the conductive layer) is t ₀ , the weight per unit area (total weight including the conductive layer) is w ₀ , and the average specific gravity is ρ, the separator porosity P _v Can be obtained by the following equation.
P _v (%) = 100 × {1− (w ₀ / [ρ · t ₀ ])}
(However, the sample area is the unit area.)
Note that the average specific gravity ρ is the specific gravity of the components of the base material such as the porous film and the conductive layer and the weight ratio per unit area as ρ _i and k _i , respectively.
ρ = 1 / (Σk _i / ρ _i )
Can be obtained at The weight ratio can be obtained by measuring the weight before and after forming the conductive layer.

{thickness}
The thickness (total thickness including the conductive layer) of the separator of the present invention is usually 5 μm or more, preferably 9 μm or more, more preferably 15 μm or more. Moreover, it is 50 micrometers or less normally, Preferably it is 35 micrometers or less, More preferably, it is 30 micrometers or less. When the thickness of the separator is in the above range, the mechanical strength is in a suitable range, and it is preferable that breakage and internal short circuit are not easily caused during high-speed winding, and battery performance can be sufficiently exhibited.

{Puncture strength}
The puncture strength of the separator of the present invention (the puncture strength of the separator including the conductive layer) is usually 250 g or more, preferably 300 g or more, more preferably 350 g or more. When the piercing strength is 250 g or more, the pressure due to expansion of the active material at the time of overcharge can be withstood, and the possibility of causing an internal short circuit is reduced. There is no particular upper limit for the piercing strength, and it does not matter if the separator characteristics such as electrical resistance satisfy the performance required from the battery performance, but it is usually 700 g or less.
In addition, the piercing strength of the separator in the present invention means strength measured by the method described below.

<Measurement of puncture strength>
A hole made of a metal (SUS440C) needle with a diameter of 1 mm and a radius of curvature of the tip of 0.5 mm is pierced at a speed of 300 mm / min in the thickness direction on a sample (measurement part: a circle with a diameter of 20 mm) fixed with a holder. Measure the maximum load.

<Meltdown temperature>
The meltdown temperature of the separator of the present invention is 170 ° C or higher, preferably 180 ° C or higher, more preferably 200 ° C or higher, and further preferably 220 ° C or higher. When the meltdown temperature is less than 170 ° C., the overcharge resistance tends to decrease. There is no particular upper limit for the meltdown temperature, and it is preferable that the separator maintain its shape up to a higher temperature. The meltdown temperature is measured by the following method.
<Measurement of meltdown temperature>
The separator of the present invention is cut out, and the four sides are fixed by being sandwiched by two aluminum plates having an outer dimension of 60 × 60 mm with a 30 × 30 mm rectangular hole. Place in a windowed oven with thermocouple to monitor temperature. The temperature at which the temperature inside the oven was increased at a rate of 5 ° C./min and the separator was visually observed and the occurrence of holes penetrating from the front to the back of the separator was recognized as the meltdown temperature.

[Non-aqueous electrolyte secondary battery]
A non-aqueous electrolyte secondary battery of the present invention includes a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte comprising a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent. In the liquid secondary battery, the separator is the separator for a non-aqueous electrolyte secondary battery of the present invention.

{Non-aqueous electrolyte solution}
<Non-aqueous solvent>
As the non-aqueous solvent of the electrolyte used in the non-aqueous electrolyte secondary battery of the present invention, any known solvent can be used as the solvent for the non-aqueous electrolyte secondary battery. For example, alkylene carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate; dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, and ethyl methyl carbonate (the alkyl group of the dialkyl carbonate is an alkyl having 1 to 4 carbon atoms) A cyclic ether such as tetrahydrofuran and 2-methyltetrahydrofuran; a chain ether such as dimethoxyethane and dimethoxymethane; a cyclic carboxylic acid ester such as γ-butyrolactone and γ-valerolactone; methyl acetate, methyl propionate and propion Examples thereof include chain carboxylic acid esters such as ethyl acid. These may be used alone or in combination of two or more.

<Electrolyte>
As the electrolyte that is the solute of the nonaqueous electrolytic solution, a lithium salt is usually used. Any lithium salt can be used, for example, an inorganic lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂₎ (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF Examples thereof include fluorine-containing organic lithium salts such as ₂ (C ₂ F ₅ SO ₂ ) ₂ . Of these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ) ₂ are preferable, and LiPF ₆ and LiBF ₄ are particularly preferable. In addition, also about lithium salt, 1 type may be used independently and 2 or more types may be used together.

  The lower limit of the concentration of these lithium salts in the non-aqueous electrolyte is usually 0.5 mol / l or more, especially 0.75 mol / l or more, and the upper limit is usually 2 mol / l or less, especially 1.5 mol / l. l or less. If the lithium salt concentration is too low, the ionic conductivity of the electrolyte may be insufficient, and if the lithium salt concentration is too high, the ionic conductivity may decrease due to an increase in the electrolyte concentration. However, battery performance tends to decrease.

<Other ingredients>
The non-aqueous electrolyte solution according to the present invention includes other useful components as required in addition to the non-aqueous solvent and the electrolyte, such as conventionally known overcharge inhibitors, dehydrating agents, deoxidizing agents, capacity maintenance after high-temperature storage. Various additives such as an auxiliary agent for improving characteristics and cycle characteristics may be contained.

  Among these, as auxiliary agents for improving capacity maintenance characteristics and cycle characteristics after high temperature storage, carbonate compounds such as vinylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, erythritan carbonate; succinic anhydride , Such as glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride Anhydrides: ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide A sulfur-containing compound of 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide, etc. Nitrogen compounds; hydrocarbon compounds such as heptane, octane, cycloheptane and the like. When the non-aqueous electrolyte contains these auxiliaries, the concentration in the non-aqueous electrolyte is usually 0.1% to 5% by weight.

{Positive electrode}
The positive electrode used for the non-aqueous electrolyte secondary battery of the present invention is usually one in which an active material layer containing a positive electrode active material and a binder is formed on a current collector.

  Examples of the positive electrode active material include materials capable of inserting and extracting lithium, such as lithium transition metal composite oxide materials such as lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide. These may be used individually by 1 type, or may use multiple types together.

  The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), SBS (styrene-butadiene-styrene elastomer), fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like can be mentioned. These may be used individually by 1 type, or may use multiple types together.

  As for the ratio of the binder in the positive electrode active material layer, the lower limit is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and the upper limit is usually 80% by weight or less, preferably 60% by weight or less, more preferably 40% by weight or less, and still more preferably 10% by weight or less. By setting it as the said range, since an active material can be hold | maintained appropriately and favorable battery performance can be exhibited, it is preferable.

  The positive electrode active material layer usually contains a conductive agent in order to increase conductivity. Examples of the conductive agent include carbonaceous materials such as graphite fine particles such as natural graphite and artificial graphite, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke. These may be used individually by 1 type, or may use multiple types together. The ratio of the conductive agent in the positive electrode active material layer is such that the lower limit is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and the upper limit is usually 50% by weight or less. , Preferably 30% by weight or less, more preferably 15% by weight or less. It is preferable to set the ratio of the conductive material within the above range because good battery performance can be exhibited.

  In addition, the positive electrode active material layer can contain additives for a normal active material layer such as a thickener.

  The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type, or may use multiple types together.

Aluminum, stainless steel, nickel-plated steel or the like is used for the current collector of the positive electrode. Although the thickness of the positive electrode current collector is arbitrary, it is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less, more preferably 20 μm or less. When the thickness of the positive electrode current collector is in the above range, the strength necessary for the current collector can be sufficiently secured, and a favorable battery capacity can be obtained. The surface electrical resistance of the positive electrode current collector is 6 × 10 ⁻³ Ω to 6 × 10 ⁻⁵ Ω with respect to the thickness of 1 μm to 100 μm, though it varies depending on the thickness in the case of the most commonly used aluminum foil. By making the surface electrical resistance of the conductive layer on the separator surface larger than this, the conductive layer can be prevented from functioning as a positive electrode current collector, and thermal degradation of the separator due to Joule heat generation can be suppressed.

  The positive electrode can be formed by applying a slurry obtained by slurrying the above-described positive electrode active material, a binder, a conductive agent, and other additives added as necessary with a solvent onto a current collector, and drying the positive electrode active material. .

  As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used individually by 1 type, or may use multiple types together. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  The thickness of the positive electrode active material layer thus formed is usually about 10 μm to 200 μm. The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

{Negative electrode}
The negative electrode used in the non-aqueous electrolyte secondary battery of the present invention is usually one in which an active material layer containing a negative electrode active material and a binder is formed on a current collector.

  As a negative electrode active material, a carbonaceous material capable of occluding and releasing lithium such as organic pyrolysate, artificial graphite and natural graphite under various pyrolysis conditions; capable of occluding and releasing lithium such as tin oxide and silicon oxide Metal oxide material; lithium metal; various lithium alloys can be used. These negative electrode active materials may be used individually by 1 type, and may mix and use 2 or more types.

  The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, and butadiene rubber. These may be used individually by 1 type, or may use multiple types together.

  The ratio of the binder in the negative electrode active material layer is such that the lower limit is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and the upper limit is usually 80% by weight or less. Preferably it is 60 weight% or less, More preferably, it is 40 weight% or less, More preferably, it is 10 weight% or less. By setting it as the said range, since an active material can be hold | maintained appropriately and favorable battery performance can be exhibited, it is preferable.

  The negative electrode active material layer may contain a conductive agent in order to further increase the conductivity. Examples of the conductive agent include carbonaceous materials such as carbon black such as acetylene black and amorphous carbon fine particles such as needle coke. These may be used individually by 1 type, or may use multiple types together. As for the ratio of the conductive agent in the negative electrode active material layer, the lower limit is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and the upper limit is usually 50% by weight or less. , Preferably 30% by weight or less, more preferably 15% by weight or less. By making the ratio of the conductive material within the above range, a favorable improvement in conductivity can be obtained, which is preferable.

  In addition, the negative electrode active material layer may contain additives for a normal active material layer such as a thickener. The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. Specific examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein. These may be used individually by 1 type, or may use multiple types together.

Copper, nickel, stainless steel, nickel-plated steel, or the like is used for the negative electrode current collector. The thickness of the negative electrode current collector is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less, more preferably 20 μm or less. When the thickness of the negative electrode current collector is in the above range, sufficient strength required for the current collector can be secured, and a favorable battery capacity can be obtained. The surface electrical resistance of the negative electrode current collector is 4 × 10 ^{−3 to} 4 × 10 ⁻⁵ Ω with respect to the thickness of 1 μm to 100 μm, although it varies depending on the thickness in the case of the most commonly used copper foil. By making the surface electrical resistance of the conductive layer on the separator surface larger than this, the conductive layer can be prevented from functioning as a negative electrode current collector, and thermal degradation of the separator due to Joule heat generation can be suppressed.

  The negative electrode can be formed by applying a slurry obtained by slurrying the above-described negative electrode active material, a binder, a conductive agent, and other additives added as necessary with a solvent onto a current collector, and then drying the negative electrode active material. .

  As the solvent used for slurrying, an organic solvent that dissolves the binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran and the like are used, but not limited thereto. These may be used individually by 1 type, or may use multiple types together. Moreover, a dispersing agent, a thickener, etc. can be added to water, and an active material can also be slurried with latex, such as SBR.

  The thickness of the negative electrode active material layer thus formed is usually about 10 μm to 200 μm. The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the active material.

{Battery shape}
The battery shape of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and can be appropriately selected from various shapes generally employed according to the application. Examples of commonly used battery shapes include a cylinder type with a sheet electrode and separator in a spiral shape, a cylinder type with an inside-out structure combining a pellet electrode and a separator, a coin type with stacked pellet electrodes and a separator, Examples include a laminate type in which a sheet electrode and a separator are laminated.

{Assembly method of non-aqueous electrolyte secondary battery}
The method for assembling the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery. For example, the separator of the present invention having a conductive layer on at least one surface, the above-described non-aqueous electrolyte, the positive electrode and the negative electrode are laminated, and the non-aqueous electrolyte is injected between the positive and negative electrodes to assemble in an appropriate shape. Manufactured by. Furthermore, other components such as an outer case can be used as necessary.

  When assembling the non-aqueous electrolyte secondary battery, when the separator of the present invention has a conductive layer only on one surface thereof, the conductive layer faces the negative electrode side even if it is laminated facing the positive electrode side. May be laminated. When the conductive material constituting the conductive layer is a metal material suitable for facing the positive electrode, it faces the positive electrode side, and when it is a metal material suitable for facing the negative electrode, it faces the negative electrode side. In general, a vigorous reaction such as decomposition of the electrolyte occurs on the positive electrode side, which is at a high potential. The details of the reason are unknown, but a short circuit of the separator due to overcharging occurs from the surface facing the positive electrode. Therefore, it is preferable to dispose the separator so that the conductive layer of the separator faces at least the positive electrode side.

{Usage}
The application of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, and can be used for various conventionally known applications. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CDs, minidiscs, and transceivers. , Electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting fixtures, toys, game devices, watches, strobes, cameras, and other small devices. The non-aqueous electrolyte secondary battery of the present invention is particularly suitable for use in large equipment such as electric vehicles and hybrid vehicles, that is, as a lithium secondary battery for EV or HEV.

The non-aqueous electrolyte secondary battery of the present invention can be used as a non-aqueous electrolyte secondary battery module in which a plurality of non-aqueous electrolyte secondary batteries are connected in series. When the non-aqueous electrolyte secondary battery of the present invention is used as a module, it is preferable that five or more are connected in series, preferably 10 or more are connected in series, and 20 or more are connected in series. preferable. In this way, by connecting a plurality of secondary batteries in series, it can be applied to a large-sized device such as an electric vehicle or a hybrid vehicle.
Moreover, when using as said non-aqueous electrolyte solution secondary battery module, it is preferable that the voltage of 20V or more is required for full charge, it is more preferable to set it as 25V or more, and it is still more preferable to set it as 30V or more.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples as long as the gist thereof is not exceeded.

  In addition, the measuring method of the surface electrical resistance and thickness of the conductive layer of the separator in the following examples and comparative examples is as follows.

<Method for measuring surface electrical resistance of conductive layer>
The measurement was performed using Lorester EP and Hirester UP manufactured by Dia Instruments (currently Mitsubishi Chemical Analytech). If the surface electrical resistance is 10 ⁶ Ω or less, use a four-probe method with a combination of Lorester EP and an ASP probe. If the surface electrical resistance is 10 ⁶ Ω or more, use a two-probe method with a combination of a Hirester UP and a UA probe. Measurements were made. The surface resistivity was obtained by using the correction factor for each probe disclosed by Mitsubishi Chemical Analytech Co., Ltd. Surface resistivity = surface electrical resistance × correction factor. The apparent volume resistivity was determined by the apparent volume resistivity = surface resistivity × thickness.

<Method for measuring thickness of conductive layer>
The thicknesses of the sputtering film and the deposited film were measured using a step / surface roughness / fine shape measuring device P-15 manufactured by KLA-Tencor.
The thickness of the coating film was measured using an upright dial gauge manufactured by Ozaki Seisakusho.

[Example 1]
<Preparation of non-aqueous electrolyte solution>
A solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) sufficiently in a ratio of 1.0 mol / l in a solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3/7 in a dry argon atmosphere. Was used as a non-aqueous electrolyte.

<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material, 90 parts by weight of LiNi _1/3 Mn _1/3 Co _1/3 O _2, 5 parts by weight of acetylene black and polyvinylidene fluoride (Kureha) 5 parts by weight of a chemical trade name “KF-1000” manufactured by Kagaku Co., Ltd. was added and mixed, and the mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. The obtained slurry was uniformly applied to both surfaces of a 15 μm-thick aluminum foil as a positive electrode current collector, dried, and then rolled to a thickness of 81 μm by a press machine. A positive electrode was cut into a shape having an uncoated part with a thickness of 100 mm and a width of 30 mm. The density of the positive electrode active material layer was 2.35 g / cm ³ .

<Production of negative electrode>
Using natural graphite powder as the negative electrode active material, 98 parts by weight of natural graphite powder, 100 parts by weight of an aqueous solution of sodium carboxymethylcellulose (concentration of 1% by weight of carboxymethylcellulose sodium) as a thickener and binder, and styrene-butadiene 2 parts by weight of an aqueous dispersion of rubber (concentration of styrene / butadiene rubber 50% by weight) was added and mixed to form a slurry. The obtained slurry was applied to both sides of a rolled copper foil having a thickness of 10 μm as a negative electrode current collector, dried, and then rolled to a thickness of 75 μm with a press machine. The active material layer had a width of 104 mm and a length of A negative electrode was cut into a shape having an uncoated part with a width of 104 mm and a width of 30 mm. The density of the negative electrode active material layer was 1.35 g / cm ³ .

<Create separator>
6.6 parts by weight of acetylene black “Denka Black HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd., 1.3 parts by weight of polyvinyl alcohol (average polymerization degree 1700, saponification degree 99% or more), alumina particles (particle size 0.2 μm, Aspect ratio 1.1) 23.4 parts by weight and 68.7 parts by weight of water were uniformly dispersed to prepare a slurry. A commercially available three-layer separator (polypropylene / polypropylene) having a thickness of 25 μm, a piercing strength of 380 g, and a porosity of 39%. Polyethylene / polypropylene) was applied to one surface as a base material, and then dried at 60 ° C. to provide a heat resistant conductive layer having a thickness of 4.8 μm. The surface electrical resistance of this conductive layer was 1.7 × 10 ⁴ Ω. The puncture strength of the separator was 380 g, the porosity was 39%, and the meltdown temperature was 190 ° C.

<Creation of battery>
32 positive electrodes and 33 negative electrodes were alternately arranged, and the above-described separator was laminated between each electrode so that the conductive layer was sandwiched opposite the positive electrode. At this time, both active material layer surfaces were positioned so as to face each other so that the positive electrode active material surface of the positive electrode did not deviate from the negative electrode active material surface of the negative electrode. Uncoated portions of the positive electrode and the negative electrode are bundled and spot-welded to produce a current collecting tab, and an electrode group is enclosed in an aluminum battery can (outside dimensions: 120 × 110 × 10 mm). . As the battery can, a battery can having a positive and negative current collecting terminal, a pressure release valve, and a non-aqueous electrolyte injection port at the lid portion was used. The current collecting tab and the current collecting terminal were connected by spot welding. Then, 20 mL of nonaqueous electrolyte solution was inject | poured into the battery can with which the electrode group was loaded, it was made to osmose | permeate an electrode sufficiently, the injection inlet was sealed, and the battery was produced.

<Overcharge test>
For a new battery that has not undergone a charge / discharge cycle, the voltage range is 4.1 to 3.0 V at 25 ° C., and the current value is 0.2 C (the current value that discharges the rated capacity with the discharge capacity of 1 hour rate in 1 hour. The initial charge / discharge was performed for 5 cycles at 1C.
Subsequently, an overcharge test was performed in the same 25 ° C. environment. Charging was performed at a constant current of 3 C from the discharged state (3 V), and the behavior was observed. Here, “valve operation” represents a phenomenon in which a gas discharge valve is activated and a non-aqueous electrolyte component is released, and “rupture” is a case where the battery container is torn violently and the contents are forcibly released. Represents a phenomenon.
The results of the overcharge test are shown in Table 1.

[Example 2]
Polymetaphenylene isophthalamide was dissolved in N, N-dimethylacetamide to prepare a 10% by weight solution as a spinning solution. The commercially available three-layer separator used in Example 1 was used as the base material, the voltage was 17 kV, the distance to the collector was 20 cm, the nozzle inner diameter was 0.59 mm, the three-layer separator was fixed on the collector, and the polyspinning was performed by electrospinning. Metaphenylene isophthalamide nanofibers were laminated. Lamination of nanofibers was performed on both sides of the separator, and lamination was performed until the thickness became 2 μm. Next, 15 parts by weight of acetylene black “Denka Black HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd., 2.7 parts by weight of polyvinyl alcohol (average polymerization degree 1700, saponification degree 99% or more) and 82.3 parts by weight of water were uniformly added. A slurry is prepared by dispersing the slurry on the surface of the separator on which the nanofibers of polymetaphenylene isophthalamide are laminated, and then dried at 60 ° C. to form a conductive layer having a thickness of 4 μm. Provided. The conductive layer had a surface electrical resistance of 712Ω. Further, the puncture strength of the separator was 380 g, the porosity was 41%, and the meltdown temperature was 220 ° C. Using the obtained separator, a battery was prepared in the same manner as in Example 1, and an overcharge test was performed. The results are shown in Table 1.

[Example 3]
Composition 1: 80% by weight of poly-4-methylpentene-1 and 20% by weight of paraffin wax Composition 2: Mixture of 30% by weight of ultra high molecular weight PE having a molecular weight of 1 million and 70% by weight of paraffin wax Mixture and composition of composition 1 The mixture of No. 2 was melt-kneaded and sheet-molded to form a multilayer sheet having a composition of composition 1 / composition 2 / composition 1 and a thickness ratio of 2/6/2 and a thickness of 200 μm. Next, the multilayer sheet was biaxially stretched at a temperature of 130 ° C. and a stretching ratio of 4 × 4 using a biaxial stretching machine. Next, after the stretched sheet was fixed on four sides, it was immersed in 2-propanol at 60 ° C. for 30 minutes to extract paraffin wax, and then 2-propanol was removed by drying at 60 ° C. to obtain a porous film. The film had a thickness of 20 μm, a puncture strength of 400 g, a porosity of 50%, and a meltdown temperature of 230 ° C. One surface of the film was subjected to Al sputtering treatment to provide a conductive layer. The thickness of the Al layer was 30 nm, and the surface electrical resistance was 20Ω. Moreover, the puncture strength of the separator formed with the Al layer was 360 g, the porosity was 50%, and the meltdown temperature was 230 ° C. Using the obtained separator, a battery was prepared in the same manner as in Example 1, and an overcharge test was performed. The results are shown in Table 1.

[Comparative Example 1]
A slurry was prepared by uniformly dispersing 1.3 parts by weight of polyvinyl alcohol (average polymerization degree 1700, saponification degree 99% or more), 25.1 parts by weight of alumina particles (particle size 0.2 μm), and 73.6 parts by weight of water. The thickness was prepared by applying a commercially available three-layer separator (polypropylene / polyethylene / polypropylene) having a thickness of 25 μm, a piercing strength of 380 g, and a porosity of 39% as a base material, followed by drying at 60 ° C. A 3.9 μm heat-resistant layer was provided. The puncture strength of this separator was 380 g, the porosity was 39%, and the meltdown temperature was 188 ° C. A battery was prepared and an overcharge test was conducted in the same manner as in Example 1 except that this separator was used. The results are shown in Table 1.

[Comparative Example 2]
Polymetaphenylene isophthalamide was dissolved in N, N-dimethylacetamide to prepare a 10% by weight solution as a spinning solution. The commercially available three-layer separator used in Example 1 was used as the base material, the voltage was 17 kV, the distance to the collector was 20 cm, the nozzle inner diameter was 0.59 mm, the three-layer separator was fixed on the collector, and the polyspinning was performed by electrospinning. Metaphenylene isophthalamide nanofibers were laminated. Lamination of nanofibers was performed on both sides of the separator, and lamination was performed until the thickness became 2 μm. The separator thus obtained had a piercing strength of 380 g, a porosity of 41%, and a meltdown temperature of 220 ° C. A battery was prepared and an overcharge test was conducted in the same manner as in Example 1 except that this separator was used. The results are shown in Table 1.

[Example 4]
A battery was prepared in the same manner as in Example 1. For a new battery that has not undergone a charge / discharge cycle, the voltage range is 4.1 to 3.0 V at 25 ° C., and the current value is 0.2 C (the current value that discharges the rated capacity with the discharge capacity of 1 hour rate in 1 hour. The initial charge / discharge was performed for 5 cycles at 1C.
Subsequently, an overcharge test was performed according to the following procedure in the same 25 ° C. environment. A battery module is formed by connecting 10 batteries that have been initially charged and discharged in series, and one battery having a lower capacity than other batteries is mixed as a virtual defective battery module. The batteries were charged with a constant current at a current value of 5 C from the fully charged state (open end voltage of each battery 4.1 V, assumed open end voltage of the battery module was 41 V), and the behavior was observed. A voltage of 50 V was applied to the battery module, but only a battery with a low capacity was opened.

[Comparative Example 3]
An overcharge test was conducted in the same manner as in Example 4 except that a battery prepared in the same manner as in Comparative Example 1 was used. A voltage of 50 V was applied to the battery module, and a battery with a low capacity burst after the valve was opened.

  From Table 1, according to the present invention, there is provided a highly safe non-aqueous electrolyte secondary battery that can prevent a short circuit and an explosion even when an overcharged state in which a voltage of several tens of volts is applied. It is clear that

Claims (14)

In a separator for use in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, The separator has a conductive layer, the apparent volume resistivity of the conductive layer is 1 × 10 ⁻⁴ Ω · cm to 1 × 10 ⁶ Ω · cm, and the meltdown temperature of the separator is 170 ° C. or higher. A separator for a non-aqueous electrolyte secondary battery. In a separator for use in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, The separator has a conductive layer, the volume resistivity of the conductive layer is 1 × 10 ⁻⁶ Ω · cm to 1 × 10 ⁶ Ω · cm, and the meltdown temperature of the separator is 170 ° C. or higher. A separator for a non-aqueous electrolyte secondary battery. In a separator for use in a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent, The separator has a conductive layer, the surface electrical resistance of the conductive layer is 1 × 10 ⁻² Ω to 1 × 10 ⁹ Ω, and the meltdown temperature of the separator is 170 ° C. or higher. Electrolyte secondary battery separator.   The separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the conductive layer includes a metal or a carbonaceous material.   5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive layer includes at least one selected from the group consisting of aluminum, molybdenum, copper, and titanium. Separator for use.   The non-aqueous electrolyte secondary solution according to claim 1, wherein the conductive layer contains at least one selected from the group consisting of graphite, carbon black, and amorphous carbon fine particles. Battery separator.   The separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the piercing strength of the separator is 250 g or more.   The separator for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the separator has a heat-resistant layer.   The separator for a non-aqueous electrolyte secondary battery according to claim 8, wherein the heat-resistant layer contains a resin having a melting point or a glass transition temperature of 170 ° C or higher.   The separator for a non-aqueous electrolyte secondary battery according to claim 9, wherein the resin in the heat-resistant layer is at least one selected from polymethylpentene, polyamide, polyimide, and polyamideimide.   The separator for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 10, wherein the heat-resistant layer in the separator contains an inorganic filler.   The separator for a non-aqueous electrolyte secondary battery according to claim 11, wherein the inorganic filler in the heat-resistant layer is at least one selected from aluminum oxide, magnesium oxide, titanium oxide, and barium sulfate. .   A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a separator, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent. A non-aqueous electrolyte secondary battery, which is the separator for a non-aqueous electrolyte secondary battery described in any one of 1 to 12.   A non-aqueous electrolyte secondary battery module comprising five or more non-aqueous electrolyte secondary batteries according to claim 13 connected in series and requiring a voltage of 20 V or more for full charge.