JP2010146960A - Nonaqueous electrolytic liquid secondary battery and positive and negative electrode for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly safe nonaqueous electrolytic liquid secondary battery wherein a porous insulating layer arranged between positive and negative electrodes has a shutdown nature and hardly causes meltdown under a high-temperature environment. <P>SOLUTION: In the nonaqueous electrolytic liquid secondary battery having the positive electrode and the negative electrode capable of occluding and discharging lithium, the porous insulating layer formed between the positive electrode and the negative electrode, and an electrolytic liquid wherein an electrolyte is dissolved into a nonaqueous solvent, the nonaqueous electrolytic liquid secondary battery includes a thermoplastic resin as a constituent component of the porous insulating layer, wherein molecular weight is 200,000-5,000,000. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery that is safe even in a high temperature environment, and a positive electrode and a negative electrode for the non-aqueous electrolyte secondary battery.

  In recent years, lithium secondary batteries, which are non-aqueous electrolyte secondary batteries with high energy density and light weight, have been used in a wide range of fields such as mobile phones and notebook personal computers with the reduction in weight and size of electrical products. Has been. 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.

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 possible 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 comprised from the liquid and the separator which consists of a polymeric porous membrane.

  A separator used in such a lithium secondary battery is required to satisfy requirements such as not impeding ion conduction between both electrodes, being able to hold an electrolytic solution, and having resistance to an electrolytic solution. ing. Also, as an important function of the separator, when the battery temperature rises due to a short circuit or overcharge condition, etc., the resin constituting the separator melts below the decomposition temperature of the electrolyte solution, closing the pores of the porous membrane There is a shutdown function that controls the thermal runaway of the battery by cutting off the current.

  Conventionally, as a separator of a lithium secondary battery, a polymer porous film mainly made of polyolefin such as polyethylene or polypropylene has been used. For example, the separator is made by uniaxial stretching or biaxial stretching as shown in Patent Documents 1 and 2. Polyolefin films are provided. Here, the stretching process is an indispensable process for imparting a certain strength to the film required for making the film porous and performing high-speed winding during battery production. However, stretching increases the mechanical strength of the film and reduces the risk of short-circuiting due to active materials and contaminants, but it leaves the film distorted and remains when exposed to high temperatures. The stress causes heat shrinkage or film breakage, so-called meltdown. Especially in EVs and HEVs that require a large capacity, a large current flows when short-circuited, so heat generation is large, and the temperature rises far beyond the melting point of the resin at a stretch. It will lead to.

  In order to prevent such a short circuit due to meltdown, a method using a porous membrane using a heat resistant resin as a separator or a composite porous membrane combining a conventional separator made of polyolefin and a heat resistant resin has been proposed (patent) References 3 and 4). However, a porous film using a heat-resistant resin naturally lacks the shutdown function of conventional separators and maintains the porous shape up to high temperatures, so that the decomposition product of the electrolyte can freely move between the positive and negative electrodes. By going back and forth and reacting with the active material, a large amount of heat was generated, leading to runaway, and sufficient safety could not always be ensured. On the other hand, in the case of a separator made of a composite porous film, the conventional separator part is used, although the part using the conventional separator material has a shutdown function, so the safety is increased compared to the case of the porous film made of a heat resistant resin alone. If the heat-resistant resin layer breaks due to the heat shrinkage stress of the material, or if the shutdown performance is lost due to meltdown of the conventional separator part without film breakage, the mass transfer between both electrodes is the same as in the case of the heat-resistant resin alone Since this occurred again, it was difficult to ensure sufficient safety.

  Similarly, in order to prevent short-circuiting due to meltdown, techniques for forming a porous layer using inorganic fine particles and the like and mixing inorganic fine particles with a porous substrate such as a heat-resistant nonwoven fabric have been proposed (Patent Documents 5 and 6). . However, even when an inorganic material is used in this way, the mass transfer between the electrodes at high temperatures cannot be controlled as in the case of the heat resistant resin, and it has been difficult to ensure sufficient safety.

Patent Document 7 proposes a battery having insulating particles between positive and negative electrodes, and there is a disclosure that shutdown is preferably performed at 120 ° C. to 130 ° C., particularly when polyethylene or the like is selected as the insulating particles. . When this insulating resin particle layer is formed by coating or the like, strain or the like usually does not remain, so shrinkage does not occur even if it melts beyond the melting point of the resin, compared to a conventional separator obtained by stretching. Safety is high. However, since these resin particle layers melt and then decrease in viscosity and increase in fluidity as the temperature rises, they are often sucked into a porous active material layer. There was a problem that it was easy to invite and it was difficult to ensure sufficient safety. That is, in Patent Document 7, there is no study on the molecular weight of polyolefin resins such as polyethylene used as insulating particles, no mention is made about the effect on the safety caused by the molecular weight, and the separator substitute in a high temperature environment. There is no disclosure about maintaining the insulating properties.
JP-A-7-304110 JP 2001-164018 A JP 2003-138057 A Japanese Patent Laid-Open No. 2001-23602 JP 2007-258160 A JP 2005-536857 A JP 2006-173001 A

  The present invention has been made in view of the above-described conventional situation, and the porous insulating layer provided between the positive and negative electrodes has a shutdown property and does not cause a meltdown even in a high temperature environment, and is highly safe. It aims at providing the positive electrode and negative electrode for non-aqueous electrolyte secondary batteries and the non-aqueous electrolyte secondary battery therefor.

  In order to solve the above-mentioned problems, the present inventors have intensively studied to form a porous insulating layer as a separator between the positive and negative electrodes. As one of the components constituting the porous insulating layer, the molecular weight is 200,000 or more, It has been found that by using a thermoplastic resin of 5 million or less as an essential component, it is possible to achieve both shutdown properties and meltdown resistance that maintains insulation without causing meltdown even at temperatures exceeding 200 ° C. The present invention has been completed.

  That is, the gist of the present invention is that a positive electrode and a negative electrode capable of inserting and extracting lithium, a porous insulating layer formed between the positive electrode and the negative electrode, and a non-aqueous system obtained by dissolving an electrolyte in a non-aqueous solvent A non-aqueous electrolyte secondary battery comprising an electrolyte solution, comprising a thermoplastic resin having a molecular weight of 200,000 or more and 5,000,000 or less as a constituent component of the porous insulating layer Battery.

  Another gist of the present invention is a positive electrode for a non-aqueous electrolyte secondary battery capable of occluding and releasing lithium, and having a porous insulating layer containing a thermoplastic resin having a molecular weight of 200,000 to 5,000,000. The present invention resides in a positive electrode for a non-aqueous electrolyte secondary battery.

  Still another subject matter of the present invention is a negative electrode for a non-aqueous electrolyte secondary battery capable of occluding and releasing lithium, comprising a porous insulating layer containing a thermoplastic resin having a molecular weight of 200,000 to 5,000,000. And a negative electrode for a non-aqueous electrolyte secondary battery.

  According to the present invention, it has a shutdown property below the decomposition temperature of the non-aqueous electrolyte solution, does not cause meltdown even at a temperature exceeding 200 ° C., and suppresses movement between positive and negative electrodes such as a decomposition product of the electrolyte solution. A non-aqueous electrolyte secondary battery that can prevent heat generation and runaway of the battery and is highly safe even in a high temperature environment is provided.

  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.

[Non-aqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode and a negative electrode capable of inserting and extracting lithium, a porous insulating layer formed between the positive electrode and the negative electrode, and an electrolyte dissolved in a non-aqueous solvent. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte solution comprising a thermoplastic resin having a molecular weight of 200,000 to 5,000,000 as a constituent component of the porous insulating layer. is there.

<Porous insulating layer>
(Thermoplastic resin with a molecular weight of 200,000 or more and 5 million or less)
The porous insulating layer formed between the positive and negative electrodes of the non-aqueous electrolyte secondary battery of the present invention is a thermoplastic having a molecular weight of 200,000 to 5,000,000 as one of the components constituting the porous insulating layer. Resin (hereinafter sometimes referred to as “high molecular weight thermoplastic resin”) is an essential component.

If the molecular weight of this high molecular weight thermoplastic resin falls below the above lower limit, the fluidity of the resin at a high temperature of 200 ° C. or higher is so high that it is sucked into the porous active material layer, so that insulation can be maintained. Have difficulty. In addition, as a standard of insulating maintenance here, as shown in the below-mentioned Example, the electrical resistance of the porous insulating layer in room temperature (usually 20-40 degreeC, 30 degreeC in the below-mentioned Example), and the porosity at 250 degreeC The electrical resistance ratio of the insulating material layer is at least 100 or more, preferably 200 or more, more preferably 500 or more. On the other hand, when the molecular weight of the high molecular weight thermoplastic resin exceeds the above upper limit, even if it exceeds the melting point, it hardly flows and does not shut down, so that the movement of the decomposition product of the electrolytic solution cannot be prevented, and the decomposition product and the electrode An exothermic reaction occurs, leading to runaway.
The molecular weight of the high molecular weight thermoplastic resin used in the present invention is preferably 300,000 or more and 5 million or less, more preferably 500,000 or more and 4 million or less, more preferably 1 million or more and 4 million or less, and most preferably 2 million or more. 3 million or less.

  The molecular weight of the thermoplastic resin in the present invention is a weight average molecular weight measured by size exclusion chromatography (SEC), but a resin having a particularly high molecular weight has a high viscosity and may be difficult to measure by SEC. In that case, if it is JIS K-7367 or ultra high molecular weight polyethylene, the viscosity average molecular weight prescribed | regulated by ASTM D4020 is made into molecular weight.

  The melt mass flow rate (MFR) of a thermoplastic resin having a molecular weight of 200,000 or more and 5 million or less in the present invention is usually 0.1 or less, preferably 0.06 or less, more preferably 0.04 or less, still more preferably. 0.02 or less. If the MFR is greater than 0.1, the fluidity of the resin at a high temperature of 200 ° C. or higher is too high, and it may be sucked into the active material layer of the porous electrode and the insulation may not be maintained. The MFR of the thermoplastic resin is measured according to JIS K-7210. The MFR values in the examples described later were measured at a temperature of 190 ° C. and a load of 2.16 kg. The unit is g / 10 minutes.

  This high molecular weight thermoplastic resin is required to have a function of blocking the current by blocking pores of the insulating layer by fluidizing the thermoplastic resin at a temperature lower than the decomposition temperature of the electrolyte. In the case of resin, the melting point is used, and in the case of amorphous resin, the glass transition point is lower than the decomposition temperature of the electrolytic solution. Therefore, the melting point of the crystalline high molecular weight thermoplastic resin or the glass transition point of the amorphous high molecular weight thermoplastic resin is 80 ° C. to 200 ° C., preferably 100 ° C. to 180 ° C., more preferably 120 ° C. to 160 ° C.

  Therefore, the high molecular weight thermoplastic resin used in the present invention is not particularly limited as long as the molecular weight is 200,000 or more and 5,000,000 or less and the thermal characteristics satisfy the above relationship with the decomposition temperature of the electrolytic solution. For example, examples of the crystalline resin include polyolefin resins such as polyethylene and polypropylene, fluorine resins such as polyvinylidene fluoride, and polyacetal. Examples of the amorphous resin include styrene resins such as polystyrene, AS, and ABS, acrylic resins such as polymethyl methacrylate, vinyl chloride resin, polycarbonate, modified polyphenylene ether, polysulfone, and polyarylate.

  Among these thermoplastic resins, the high molecular weight thermoplastic resin having a molecular weight of 200,000 or more and 5,000,000 or less used as an essential component of the porous insulating layer in the present invention is a polyolefin resin from the viewpoint of heat resistance and electrolytic solution resistance. In particular, polyethylene and polypropylene are preferably used from the viewpoint of the temperature and reliability of the shutdown performance.

  These high molecular weight thermoplastic resins may be used individually by 1 type, and may use 2 or more types together.

(Other ingredients)
If the porous insulating layer formed between the positive and negative electrodes in the present invention contains the above-described high molecular weight thermoplastic resin as an essential component as one of the components constituting the porous insulating layer, other thermoplastic resins Or a thermosetting resin or an inorganic substance.

  Examples of the other components include thermoplastic resins having a molecular weight of less than 200,000. In order to sufficiently obtain the above-described effects of the high molecular weight thermoplastic resin used as an essential component in the present invention, the porous insulating layer The proportion of the high molecular weight thermoplastic resin in all the constituent components is usually 50% by weight or more, particularly preferably 60% by weight or more, and more preferably 75% by weight or more.

  In the examples described later, atactic polypropylene having a molecular weight of 180,000 is used as a component for thickening the slurry and binding resin particles together. As such a binder component, atactic polypropylene is used. However, any material other than atactic polypropylene can be used as long as it is soluble in the solvent of the slurry at room temperature and has an affinity for the resin particles. For example, if the resin particles are polyethylene or polypropylene particles and the solvent is xylene or toluene, one or more elastomers such as SBS (styrene-butadiene-styrene elastomer) can be used. When these binder components are used, the proportion is 1 to 10% by weight, preferably 2 to 8% by weight, more preferably 3 to 6% by weight, based on the total components of the porous insulating layer to be formed. It is. If the binder component is less than 1% by weight, the effect of binding the resin particles may be insufficient. If the binder component exceeds 10% by weight, a film is formed on the surface of the porous insulating layer or electrode after drying and removing the solvent. This may cause an increase in electrical resistance and may lead to a decrease in battery characteristics such as output.

(Resin particles)
The porous insulating layer according to the present invention is preferably formed of fine particles of the above-described high molecular weight thermoplastic resin in order to prevent the growth of acicular crystals of lithium and to lower the electrical resistance. Further, it is also preferable for reducing thermal shrinkage caused by a molding process such as residual stress.
In this case, the average particle size of the resin particles is preferably 0.1 to 200 μm, particularly 0.5 to 150 μm. If the average particle size of the resin particles is smaller than the lower limit, the particles are likely to aggregate and are difficult to handle, which is not preferable. On the other hand, if the average particle size of the resin particles exceeds the above upper limit, the distance between the positive and negative electrodes is increased, the resistance is increased and the battery characteristics are lowered, which is not preferable.

  In addition, the average particle diameter of this resin particle can be obtained by taking the average of the particle diameter obtained by laser diffraction method prescribed | regulated, for example by JISZ-8825-1, etc., or SEM observation.

(Porosity)
The porous insulating layer according to the present invention has a porosity of 30 to 90%, particularly 50 to 80%, particularly 60, as a degree of porosity. The porosity (volume ratio of voids to the apparent total volume of the porous insulating layer) is 30 to 90%. It is preferable to be 70%. If the porosity of the porous insulating layer is smaller than the lower limit, the electrical resistance may be too high, and battery performance such as output may be deteriorated. When the porosity is larger than the above upper limit, the mechanical strength is too low, and the shape cannot be maintained when the active material expands / shrinks due to charge / discharge, which may cause an internal short circuit.

The porosity of the porous insulating layer in the present invention is determined by the weight method as follows.
That is, first, the thickness (t0) and weight (w0) of the electrode before forming the porous insulating layer are measured. Next, after forming the porous insulating layer, the thickness (t1) and weight (w1) of the electrode / porous insulating layer are measured. When the specific gravity of the resin forming the porous insulating layer is ρ0, the porosity Pv of the porous insulating layer can be obtained by the following equation.
Pv (%) = 100 × {1- (ρ1 / ρ0)}
(However, ρ1 = (w1-w0) / (t1-t0), sample area is unit area)

(thickness)
The thickness of the porous insulating layer according to the present invention varies depending on the scale and use of the non-aqueous electrolyte secondary battery to which the porous insulating layer is applied, the formation method of the porous insulating layer, etc. When the porous insulating layer is formed by this coating method, the thickness of the porous insulating layer is preferably 0.1 to 200 μm, more preferably 0.5 to 150 μm. If the thickness of the porous insulating layer is thinner than this lower limit, defects and the like are likely to occur, which is not preferable. On the other hand, if the thickness of the porous insulating layer exceeds this upper limit, the distance between the positive and negative electrodes is increased, the resistance is increased, and the battery characteristics are deteriorated.

(Formation method)
The method for forming the porous insulating layer according to the present invention is not particularly limited, and a known method is used. For example, when forming a porous insulating layer composed of fine resin particles, a slurry of resin particles is prepared, and this slurry is a known method such as doctor blade or roll coater, die coater, and other dipping and spraying methods. Then, it is applied to a surface where a porous insulating layer such as an electrode active material layer is formed, and then the solvent is dried to form a porous insulating layer.

  The type of solvent used and the drying means are not particularly limited, and known solvents and known drying means are appropriately used. Examples of the solvent include aromatics such as xylene and toluene when the resin particles are polyethylene or polypropylene. 1 type or 2 or more types of alicyclic hydrocarbons such as aromatic hydrocarbons, decalin, tetralin, etc. are used, and resin particles are dispersed in such a solvent at a concentration of about 1 to 40% by weight to prepare a slurry. it can. The drying temperature is usually 80 ° C. to the melting point of the resin particles −20 ° C., although it depends on the type of solvent. Further, hot air may be blown to increase the drying efficiency.

  In this case, the resin particles used are only dissolved in the solvent and are not dissolved. Therefore, the average particle size of the resin particles in the slurry becomes the average particle size of the resin particles in the formed porous insulating layer. .

  As another method of forming the porous insulating layer, a polymer solution is prepared by dissolving a high molecular weight thermoplastic resin in a solvent, and the surface of the porous insulating layer such as an electrode active material layer is formed by a known method as described above. There is a method in which a porous insulating layer is formed by solidifying a resin that has been applied and then immersed in a poor solvent of a thermoplastic resin to dissolve it.

(Combined use with other separators)
Although the porous insulating layer according to the present invention is provided between the positive and negative electrodes, a conventionally known separator may be laminated on the porous insulating layer and interposed between the positive and negative electrodes. In this case, the porous insulating layer may be formed on the active material layer of the positive electrode, the active material layer of the negative electrode, or the active material layer of both electrodes, or may be formed on at least one side of the separator. Moreover, a conventionally known nonwoven fabric may be laminated on the porous insulating layer according to the present invention instead of the separator and interposed between the positive and negative electrodes. In this case, the porous insulating layer may be formed on the active material layer of the positive electrode, the active material layer of the negative electrode, or the active material layer of both electrodes, or may be formed on at least one side of the nonwoven fabric.

<Non-aqueous electrolyte>
(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.

(Electrolytes)
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 Fluorine-containing organic lithium salts such as ₂ (C ₂ F ₅ SO ₂ ) ₂ are included. Among 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. When the concentration of the lithium salt exceeds this upper limit value, the viscosity of the nonaqueous electrolytic solution increases and the electrical conductivity also decreases. Moreover, since electrical conductivity will become low if less than this lower limit, it is preferable to prepare a non-aqueous electrolyte within the said concentration range.

(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.

  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 and erythritan carbonate; succinic anhydride, anhydrous glutar Carboxylic acid anhydrides such as acid, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride; Sulfur containing ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide, etc. Compound; Nitrogen-containing compound such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide; Examples thereof include hydrocarbon compounds such as heptane, octane, and cycloheptane. 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. If the proportion of the binder is small, the active material cannot be sufficiently retained, so that the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the contrary, if the amount is too large, the battery capacity and conductivity are lowered. It will be.

  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. If the proportion of the conductive agent is small, the conductivity may be insufficient, and conversely if too large, the battery capacity may be reduced.

  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. If the thickness of the positive electrode current collector is thinner than the above range, the strength required for the current collector may be insufficient. On the other hand, if the thickness of the current collector is larger than the above range, the volume ratio of the active material put in the battery is lowered, and the required battery capacity may not be obtained.

  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 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.

  The positive electrode for a non-aqueous electrolyte secondary battery of the present invention is formed on the active material layer of a conventional positive electrode for a non-aqueous electrolyte secondary battery obtained by forming a positive electrode active material layer on a current collector in this way. The porous insulating layer according to the present invention is formed according to the method for forming a porous insulating layer described above. The thickness of the porous insulating layer is determined based on the scale and use of the non-aqueous electrolyte secondary battery to which the positive electrode for the non-aqueous electrolyte secondary battery is applied, whether or not other separators and non-woven fabrics are used in combination, and the non-aqueous system to be applied. Although it varies depending on the presence or absence of the porous insulating layer of the negative electrode for the electrolyte secondary battery, it is usually 0.1 to 200 μm, preferably 0.5 to 150 μm.

<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. If the ratio of the binder is small, the active material cannot be sufficiently retained, so that the negative electrode mechanical strength may be insufficient, and the battery performance such as cycle characteristics may be deteriorated. become.

  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 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. 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. When the proportion of the conductive agent is less than the above range, the required conductivity improvement effect may not be obtained, and when the proportion of the conductive agent is greater than the above range, the active material ratio decreases and the necessary conductivity is reduced. It may not be obtained.

  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. If the thickness of the negative electrode current collector is thinner than the above range, the strength required for the current collector may be insufficient. On the other hand, if the thickness of the current collector is larger than the above range, the volume ratio of the active material put in the battery is lowered, and the required battery capacity may not be obtained.

  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 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.

  The negative electrode for a non-aqueous electrolyte secondary battery of the present invention is formed on the active material layer of a conventional negative electrode for a non-aqueous electrolyte secondary battery obtained by forming a negative electrode active material layer on a current collector in this way. The porous insulating layer according to the present invention is formed according to the method for forming a porous insulating layer described above. The thickness of the porous insulating layer is determined based on the scale and use of the non-aqueous electrolyte secondary battery to which the negative electrode for the non-aqueous electrolyte secondary battery is applied, whether or not other separators and nonwoven fabrics are used in combination, and the non-aqueous system to be applied. Although it depends on the presence or absence of the porous insulating layer of the positive electrode for the electrolyte secondary battery, it is usually 0.1 to 200 μm, preferably 0.5 to 150 μm.

<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. In the present invention, a separator is not always necessary, and a porous insulating layer integrated with an electrode can serve as a separator. Alternatively, the porous insulating layer of the present invention and the separator may be used in combination in order to further increase the safety-related reliability.

<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 porous insulating layer according to the present invention, the above-described non-aqueous electrolyte, the positive electrode and the negative electrode, and if necessary, a conventionally known separator or non-woven fabric is used. It is manufactured by laminating other separators and non-woven fabrics used, injecting a non-aqueous electrolyte between positive and negative electrodes, and assembling into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary. Moreover, it manufactures by using the negative electrode and / or positive electrode which formed the porous insulating layer concerning this invention previously, making these oppose and assembling into an appropriate shape.

<Application>
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 equipment, toys, gaming devices, small devices such as watches, strobes and cameras, and large devices such as electric vehicles and hybrid vehicles Can be mentioned.

  EXAMPLES 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.

[Example 1]
<Preparation of non-aqueous electrolyte solution>
Under a dry argon atmosphere, sufficiently dried LiBF ₄ was dissolved in propylene carbonate at a ratio of 1.0 mol / l, and TOP (trioctyl phosphate) as a surfactant was added at a concentration of 1 wt. % To obtain a non-aqueous electrolyte solution.

<Preparation of positive electrode>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material, 10 parts by weight of acetylene black and polyvinylidene fluoride (Kureha) were added to 85 parts by weight of LiNi _1/3 Mn _1/3 Co _1/3 O _2. 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. This was uniformly applied to one side of a 15 μm-thick aluminum foil as a positive electrode current collector, dried, and then pressed by a press machine so that the density of the positive electrode active material layer was 2.6 g / cm ^3. A positive electrode active material layer having a thickness of 60 μm was formed as a positive electrode.

<Production of negative electrode>
Using natural graphite powder as the negative electrode active material, 94 parts by weight of natural graphite powder is mixed with 6 parts by weight of polyvinylidene fluoride (trade name “KF-1000” manufactured by Kureha Chemical Co., Ltd.), and the mixture is mixed with N-methyl-2-pyrrolidone. It was dispersed to form a slurry. This was uniformly applied to one side of a 9 μm-thick copper foil as a negative electrode current collector, dried, and then pressed by a pressing machine so that the density of the negative electrode active material layer was 1.45 g / cm ^3. A negative electrode active material layer having a thickness of 49 μm was formed as a negative electrode.

<Formation of porous insulating layer>
In a 3 wt% xylene solution of atactic polypropylene (weight average molecular weight = 180,000), ultra high molecular weight polyethylene ("Mipelon XM220" manufactured by Mitsui Chemicals, Inc.), viscosity average molecular weight (ASTM D4020) = 2 million, melting point = 136 ° C, average A slurry was prepared in which particle size = 30 μm, MFR <0.01) was dispersed at a solid content concentration (ultra high molecular weight polyethylene concentration) of 23% by weight. This slurry was applied onto the negative electrode active material layer of the negative electrode produced above using a 200 μm applicator, and then dried in a hot air oven at 80 ° C. for 1 hour to remove xylene from the coating film. The thickness of the coating film on the negative electrode was 64 μm. When the resistance of the copper foil and the coating film was measured with a tester, it was 1 MΩ or more, and an insulating layer was formed.

<Resistance measurement>
The positive electrode and the negative electrode on which the porous insulating layer is formed are cut into a circular shape having a diameter of 10 mm and a square of 2 cm × 2 cm, respectively, and the positive electrode active material layer of the positive electrode and the porous insulating layer of the negative electrode are opposed to each other. Combined and impregnated with non-aqueous electrolyte. The sample assembled by laminating both electrodes in this way is set in an impedance measurement cell, and the AC impedance is measured under a condition of 2 KHz using a milliohm meter (Agilent Technology 4338B), and its real part Z ′ is made porous. The electrical resistance of the quality insulating layer was used.
The temperature was raised at a rate of 5 ° C. per minute, and the resistance of the porous insulating layer at room temperature (30 ° C.) and 250 ° C. was measured. The results are shown in Table 1. In addition, the measurement area of electric resistance was made into the positive electrode area 0.785 cm < ² >.

[Example 2]
To a 3% by weight xylene solution of atactic polypropylene used in Example 1, ultrahigh molecular weight polyethylene (“Hi-Zex Million 030S” manufactured by Mitsui Chemicals, Inc., weight average molecular weight = 300,000, melting point = 136 ° C., average particle size = 120 μm, A slurry in which MFR = 0.01) was dispersed at a solid content concentration (ultra high molecular weight polyethylene concentration) of 40% by weight was prepared. This slurry was applied onto the negative electrode active material layer of the negative electrode produced above using a 200 μm applicator, and then dried in a hot air oven at 80 ° C. for 1 hour to remove xylene from the coating film. The thickness of the coating film on the negative electrode was 320 μm. When the resistance of the copper foil and the coating film was measured with a tester, it was 1 MΩ or more, and an insulating layer was formed.
Using this porous insulating layer-formed negative electrode, the electrical resistance was measured in the same manner as in Example 1. The results are shown in Table 1.

Example 3
In a 3% by weight xylene solution of atactic polypropylene used in Example 1, high density polyethylene (“Hi-Zex 7000FP” manufactured by Prime Polymer Co., Ltd., weight average molecular weight = 200,000, melting point = 131 ° C., average particle size = 50 μm, MFR = 0.04) was dispersed at a solid content concentration (high density polyethylene concentration) of 40% by weight to prepare a slurry. This slurry was applied onto the negative electrode active material layer of the negative electrode produced above using a 200 μm applicator, and then dried in a hot air oven at 80 ° C. for 1 hour to remove xylene from the coating film. The thickness of the coating film on the negative electrode was 115 μm. When the resistance of the copper foil and the coating film was measured with a tester, it was 1 MΩ or more, and an insulating layer was formed.
Using this porous insulating layer-formed negative electrode, the electrical resistance was measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
To a 3% by weight xylene solution of atactic polypropylene used in Example 1, low density polyethylene (“SK-PE-20L” manufactured by Seishin Enterprise Co., Ltd., weight average molecular weight = 180,000, melting point = 103 ° C., average particle size = 20 μm) , MFR = 24) was dispersed at a solid content concentration (low density polyethylene concentration) of 23% by weight. This slurry was applied onto the negative electrode active material layer of the negative electrode produced above using a 200 μm applicator, and then dried in a hot air oven at 80 ° C. for 1 hour to remove xylene from the coating film. The thickness of the coating film on the negative electrode was 72 μm. When the resistance of the copper foil and the coating film was measured with a tester, it was 1 MΩ or more, and an insulating layer was formed.
Using this porous insulating layer-formed negative electrode, the electrical resistance was measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
To a 3% by weight xylene solution of atactic polypropylene used in Example 1, high density polyethylene (“HY430P” manufactured by Nippon Polyethylene Co., Ltd., weight average molecular weight = 180,000, melting point = 135 ° C., average particle size = 200 μm, MFR = 0 .8) was dispersed at a solid content concentration (high density polyethylene concentration) of 23% by weight. This slurry was applied onto the negative electrode active material layer of the negative electrode produced above using a 200 μm applicator, and then dried in a hot air oven at 80 ° C. for 1 hour to remove xylene from the coating film. The thickness of the coating film on the negative electrode was 415 μm. When the resistance of the copper foil and the coating film was measured with a tester, it was 1 MΩ or more, and an insulating layer was formed.
Using this porous insulating layer-formed negative electrode, the electrical resistance was measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
A commercially available battery separator ("Celgard 2325" manufactured by Celgard) produced by stretching was cut into a size of 2 cm x 2 cm and used.
The positive electrode and the negative electrode are cut into a circular shape with a diameter of 10 mm and a square with a size of 2 cm × 2 cm, and with the active material layers facing each other, the above-mentioned commercially available separator is sandwiched between the two electrodes, and the electrolytic solution is added. Impregnated. Using the sample assembled in this manner, the electrical resistance was measured in the same manner as in Example 1. The results are shown in Table 1.

  In Table 1, the ratio of the measured value of electrical resistance at 250 ° C. to the measured value of electrical resistance at 30 ° C. in each example (250 ° C./30° C.) is shown as the high-temperature short-circuit prevention property.

Table 1 shows the following.
In Examples 1 to 3 in which the porous insulating layer is formed using polyethylene having a molecular weight of 200,000 or more, sufficient insulation is maintained even at a high temperature exceeding the melting point of the used polyethylene by 100 ° C. or more. As described above, this high molecular weight polyethylene has a high molecular weight and thus has a high viscosity and low fluidity even when melted. Therefore, it is not sucked into the porous active material layer, so This is because the film stays on the surface of the material layer in a molten film state, and as a result, occurrence of a short circuit at a high temperature can be well prevented.

  On the other hand, in Comparative Examples 1 and 2 in which the porous insulating layer was formed using polyethylene having a molecular weight of less than 200,000, the resistance at a high temperature of the porous insulating layer was smaller by one digit or more than in Examples 1 to 3, Insulation is greatly reduced. This is because the polyethylene used has a low molecular weight and has a high fluidity when melted. As a result, the resin is sucked into the porous active material layer of the electrode, particularly the negative electrode active material layer having a large gap. Is presumed to be due to the occurrence of a slight short circuit.

  In addition, as shown in Comparative Example 3, the commercially available separator produced by stretching has a lower resistance at a higher temperature than Comparative Examples 1 and 2, but as described above, this is a meltdown due to heat shrinkage. This is thought to be due to the ongoing progress.

  In addition, when the porous insulating layer formed in Examples 1-3 was investigated with the electron microscope, all the porous insulating layers were formed as the aggregate | assembly of the resin particle. Moreover, it was confirmed that the porosity of the porous layer investigated by the above-mentioned method is about 70%.

Claims (16)

  Non-aqueous electrolysis comprising a positive electrode and a negative electrode capable of inserting and extracting lithium, a porous insulating layer formed between the positive electrode and the negative electrode, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent In the liquid secondary battery, a non-aqueous electrolyte secondary battery comprising a thermoplastic resin having a molecular weight of 200,000 to 5,000,000 as a constituent component of the porous insulating layer.   2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thermoplastic resin is a polyolefin resin.   The non-aqueous electrolyte secondary battery according to claim 2, wherein the polyolefin resin is polyethylene and / or polypropylene.   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the thermoplastic resin is resin particles having an average particle diameter of 0.1 to 200 [mu] m. .   5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the porous insulating layer is formed in contact with the positive electrode and / or the negative electrode. 6. .   6. The non-aqueous electrolyte secondary battery according to claim 5, wherein the porous insulating layer is formed by applying and drying a slurry of the thermoplastic resin particles. battery.   A positive electrode for a non-aqueous electrolyte secondary battery capable of inserting and extracting lithium, comprising a porous insulating layer containing a thermoplastic resin having a molecular weight of 200,000 or more and 5,000,000 or less. Positive electrode for liquid secondary battery.   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 7, wherein the thermoplastic resin is a polyolefin resin.   The positive electrode for a non-aqueous electrolyte secondary battery according to claim 8, wherein the polyolefin resin is polyethylene and / or polypropylene.   10. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 7, wherein the thermoplastic resin is a resin particle having an average particle size of 0.1 to 200 μm. Positive electrode for secondary battery.   11. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 10, wherein the porous insulating layer is formed by applying and drying a slurry of the thermoplastic resin particles. Secondary battery positive electrode.   A negative electrode for a non-aqueous electrolyte secondary battery capable of occluding and releasing lithium, comprising a porous insulating layer containing a thermoplastic resin having a molecular weight of 200,000 or more and 5,000,000 or less. Negative electrode for liquid secondary battery.   The negative electrode for a nonaqueous electrolyte secondary battery according to claim 12, wherein the thermoplastic resin is a polyolefin resin.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 13, wherein the polyolefin resin is polyethylene and / or polypropylene.   15. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 12, wherein the thermoplastic resin is resin particles having an average particle diameter of 0.1 to 200 μm. Negative electrode for secondary battery.   The negative electrode for a non-aqueous electrolyte secondary battery according to claim 15, wherein the porous insulating layer is formed by applying and drying a slurry of the thermoplastic resin particles. Negative electrode for secondary battery.