JP5422373B2 - Battery separator and non-aqueous lithium secondary battery - Google Patents

Description

  The present invention relates to a battery separator and a non-aqueous lithium secondary battery incorporating the battery separator, and in particular, the battery separator has an appropriate surface roughness and is suitable as a battery separator for a non-aqueous lithium secondary battery. It can be used for.

  Secondary batteries are widely used as power sources for portable electronic devices such as OA, FA, home appliances, and communication devices. In particular, portable devices using non-aqueous lithium secondary batteries are increasing because they have high volumetric efficiency when mounted on devices and lead to miniaturization and weight reduction of the devices.

  On the other hand, large rechargeable batteries are being researched and developed in many fields related to environmental issues such as road leveling, UPS, and electric vehicles, and are excellent in large capacity, high output, high voltage, and long-term storage. Accordingly, the use of non-aqueous lithium secondary batteries, which are a type of secondary battery, is expanding.

  The working voltage of the non-aqueous lithium secondary battery is usually designed with an upper limit of 4.1 to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages.

  As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of causing more lithium ions to be present is used, and organic carbonates such as polypropylene carbonate and ethylene carbonate are used as the high dielectric constant organic solvent. Yes. As a supporting electrolyte that becomes a lithium ion source in the solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.

  The separator of the non-aqueous lithium secondary battery is required to be insulative from the viewpoint of preventing an internal short circuit by directly contacting the positive electrode and the negative electrode and interposing between the two electrodes. Moreover, it is necessary to have a microporous structure in order to provide air permeability as a lithium ion passage and a function of diffusing and holding the electrolyte. Inevitably, a porous film is used as the separator.

  Recently, improvement in battery performance has been demanded due to an increase in the amount of electricity consumed by products such as mobile phones and PDAs, or power tools. In addition, from the viewpoint of environmental problems, etc., application to hybrid electric vehicles, plug-in hybrid vehicles, electric vehicles, etc. has been studied, and higher battery performance is required. Improvement of characteristics of battery members such as a negative electrode, an electrolyte, and a separator is being promoted.

  Japanese Patent Application Laid-Open No. 11-060791 (Patent Document 1) proposes a porous film made of polyethylene and application of the film to a separator as a technique for improving the characteristics of the separator. Japanese Patent No. 4049416 (Patent Document 2) also proposes a polyethylene porous film using a roughening agent and application of the film to a separator as a technique for improving the characteristics of the separator.

  A separator in which polypropylene and polyethylene are laminated has been proposed (Japanese Patent No. 2883726: Patent Document 3).

JP-A-11-060791 Japanese Patent No. 4049416 Japanese Patent No. 2883726

However, the polyethylene resin separator obtained by Patent Document 1 or 2 has room for improvement with respect to the safety of the battery, in particular, the heat resistance of the separator, with the recent increase in capacity of the battery. Furthermore, when an inorganic filler is used as a roughening agent, the mass per unit area is increased by the addition thereof, which is a contradictory direction from the viewpoint of reducing the weight of the battery.
In the separator described in Patent Document 3, although the safety of the battery is ensured, there is room for improvement in terms of surface properties, particularly arithmetic average roughness, from the viewpoint of improving battery performance. there were.

  This invention is made | formed in view of the said problem, and makes it a subject to obtain the battery separator which has heat resistance and improves a battery characteristic using the porous film which has polyolefin resin as a main component.

In order to solve the above-mentioned problems, the present invention provides a film-like product obtained by laminating a resin composition mainly composed of a polypropylene- based resin having β activity and another resin composition by a co-extrusion method. It consists of a laminated porous film formed by biaxial stretching,
Porous layer mainly composed of polypropylene resin having the β activity is arranged on at least one side surface, the arithmetic mean roughness Ra of the surface is not less 0.3μm or more, the longitudinal direction of the separator in the separator both surfaces The battery separator is characterized in that the ratio Ra1 / Ra2 comprising the arithmetic average roughness Ra1 and the arithmetic average roughness Ra2 in the width direction is 0.80 to 1.20.

As a result of intensive studies on the above problems, the present inventors have succeeded in obtaining a battery separator capable of solving the above-described conventional techniques, and have completed the present invention.
As a result of intensive studies by the inventor, the battery separator preferably has a surface arithmetic average roughness Ra of 0.3 μm or more, more preferably 0.35 μm or more, and further preferably 0.50 μm or more. I found out that there was.
Specifically, as a result of producing a battery using the battery separator of the present invention, a difference occurs in battery cycle characteristics depending on the calculated average roughness Ra of the separator. In particular, the arithmetic average roughness Ra of the separator is 0. It was found that it is preferably 30 μm or more. Although details are still unclear, when the arithmetic average roughness Ra is 0.30 μm or more, the portion where the electrolyte accumulates on the separator surface increases, that is, by improving the liquid retention of the separator electrolyte, This is thought to have greatly contributed to the improvement of cycle characteristics.
The upper limit is not particularly limited, but is preferably 10 μm or less. When it is 10 μm or less, it is particularly preferable when it is used as a thin separator that sufficiently retains the liquid retention of the electrolyte and requires a thickness accuracy.
Further, as described above, the battery separator of the present invention has a ratio Ra ₁ / Ra ₂ composed of the arithmetic average roughness Ra _{1 in} the longitudinal direction of the separator on both sides of the separator and the arithmetic average roughness Ra _{2 in the} width direction. 0.80 to 1.20.
When Ra ₁ / Ra ₂ is in the range of 0.80 to 1.20, the portion where the electrolyte is accumulated is isotropic, there is no unevenness in the electrolyte retention, and the cycle characteristics of the battery from this point It can contribute to improvement. The ratio Ra ₁ / Ra ₂ is more preferably 0.85 to 1.15.

Further, the battery separator of the present invention, ing is biaxially oriented.
In order to give the above-mentioned surface roughness, the stretching condition is a point, and by selecting the stretching condition, Ra, Ra1 / Ra2, and the like can be set within a set range.

In the battery separator of the present invention, at least one outer layer of the battery separator has a laminated structure of a layer mainly composed of a polypropylene resin and a layer composed of another resin composition .
Since the polypropylene resin is excellent in heat resistance, it can contribute to safety and is excellent in workability.

The battery separator of the present invention, that having a β activity.
Specifically, the surface can be roughened as described above, assuming that the polypropylene resin has β activity using a β crystal nucleating agent.

Further, the present invention provides a nonaqueous lithium secondary battery using the separator the cell.
Furthermore, the manufacturing method of the said battery separator is provided .

The battery separator of the present invention is excellent in improving the battery characteristics while improving the cycle characteristics of the battery due to excellent electrolyte retention and maintaining the breakdown characteristics (hereinafter referred to as BD characteristics) as heat resistance. A battery separator can be provided.
Moreover, in the non-aqueous lithium secondary battery provided with the battery separator of the present invention, the battery retention characteristics, output characteristics, particularly battery characteristics such as low temperature output are improved.

(A) (B) is a figure explaining the fixing method of the separator for batteries in X-ray diffraction measurement.

Hereinafter, embodiments of the battery separator of the present invention will be described in detail.
In the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. The content ratio of the components is not specified, but the main component includes 50% by mass or more, preferably 70% by mass or more, particularly preferably 90% by mass or more (including 100%) in the composition. It is.
Further, when “X to Y” (X and Y are arbitrary numbers) is described, “X to Y” is intended unless otherwise specified, and “it is preferably larger than X and smaller than Y”. Includes intentions.

In the present invention, it is important to have a porous layer (A layer) mainly composed of a polypropylene resin having β activity .

  Next, the polypropylene resin will be described. The polypropylene resin in the present invention is homopolypropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene or 1-decene. And a random copolymer or a block copolymer with an α-olefin. Among these, when used for a battery separator, homopolypropylene is more preferably used from the viewpoint of mechanical strength.

The polypropylene resin preferably has an isotactic pentad fraction exhibiting stereoregularity of 80 to 99%, more preferably 83 to 98%, and still more preferably 85 to 97%. use. If the isotactic pentad fraction is too low, the mechanical strength of the battery separator may decrease. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit that can be obtained industrially at present, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.
The isotactic pentad fraction is a three-dimensional structure in which five methyl groups that are side chains are located in the same direction with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Or the ratio is meant. Signal assignment of the methyl group region is as follows. Zambelli et at al. (Macromol. 8, 687 (1975)).

  Moreover, it is preferable that Mw / Mn which is a parameter which shows molecular weight distribution of a polypropylene resin is 1.5-10.0. More preferably, 2.0 to 8.0, and still more preferably 2.0 to 6.0 is used. This means that the smaller the Mw / Mn, the narrower the molecular weight distribution. However, if the Mw / Mn is less than 1.5, problems such as a decrease in extrusion moldability occur, and it is difficult to produce industrially. There are many cases. On the other hand, when Mw / Mn exceeds 10.0, the low molecular weight component increases, and the mechanical strength of the obtained battery separator tends to decrease. Mw / Mn is obtained by GPC (gel per emission chromatography) method.

  Further, the melt flow rate (MFR) of the polypropylene resin is not particularly limited, but usually the MFR is preferably 0.1 to 15 g / 10 minutes, and preferably 0.5 to 10 g / 10 minutes. It is more preferable. When the MFR is less than 0.1 g / 10 minutes, the melt viscosity of the resin during the molding process is high, and the productivity is lowered. On the other hand, when it exceeds 15 g / 10 minutes, practical problems such as insufficient strength of the obtained battery separator tend to occur. MFR is measured under the conditions of a temperature of 230 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  Examples of the polypropylene resin include trade names “Novatech PP” “WINTEC” (manufactured by Nippon Polypro), “Versify” “Notio” “Tafmer XR” (manufactured by Mitsui Chemicals), “Zeras” “Thermolan” (Mitsubishi Chemical) , “Sumitomo Noblen”, “Tough Selenium” (manufactured by Sumitomo Chemical), “Prime TPO” (manufactured by Prime Polymer), “Adflex”, “Adsyl”, “HMS-PP (PF814)” (manufactured by Sun Aroma), “ Commercially available products such as “Inspire” (manufactured by Dow Chemical Co., Ltd.) can be used.

  In the battery separator of the present invention, it is important that the arithmetic average roughness Ra of at least one surface is 0.3 μm or more. Examples of the method for providing the surface roughness include a method using sandblasting and a method using a surface roughening agent, and are not particularly limited.

  For example, a fine particle roughening agent can be used as one of the roughening agents. Examples of the fine particle roughening agent include inorganic fillers and organic fillers which are generally referred to, but are not particularly limited as long as they can be extruded together with a polyolefin resin to form a film.

  Examples of inorganic fillers include 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, aluminum oxide and oxidation In addition to oxides such as calcium, magnesium oxide, zinc oxide, titanium oxide, and silica, silicates such as talc, clay, and mica can be used. Among these, barium sulfate and aluminum oxide are preferable.

  As the organic filler, resin particles having a crystal melting peak temperature higher than the stretching temperature are preferable so that the filler does not melt at the stretching temperature, and crosslinked resin particles having a gel fraction of about 4 to 10% are more preferable. Examples of organic fillers include ultra high molecular weight polyethylene, polystyrene, polymethyl methacrylate, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polytetrafluoroethylene, polyimide, polyether. Examples thereof include thermoplastic resins such as imide, melamine, and benzoguanamine, and thermosetting resins. Among these, cross-linked polystyrene and the like are particularly preferable.

  As an average particle diameter of a roughening agent, about 0.1-50 micrometers is preferable, More preferably, it is 0.3-10 micrometers, More preferably, it is 0.5-5 micrometers. When the average particle size is less than 0.1 μm, the dispersibility is reduced due to the aggregation of the surface roughening agents to cause uneven stretching, and the contact area of the interface between the thermoplastic resin and the surface roughening agent increases. Extrusion is difficult, and it tends to adversely affect the porosity. On the other hand, when the average particle size exceeds 50 μm, it is difficult to make the battery separator thin, and the mechanical strength of the battery separator is significantly lowered, which is not preferable.

  The addition amount of the surface roughening agent may be arbitrarily set within a range that does not impair the physical properties of the final battery separator, but considering the moldability in an extruder, it is usually 1 to 70% by mass of the battery separator. Is more preferable, and about 5 to 50% by mass is more preferable.

In the present invention, in addition to the polypropylene resin and the surface roughening agent, various known additives such as an antioxidant are added in a range of about 0.01 to 5% by mass as necessary. May be. Examples of a method for manufacturing a battery separator of the present invention formed by using the raw material components described above, for example, a roughening agent and polypropylene resin kneaded dispersion, coextruded film form, the biaxial extension Shin Thus, there is a method of obtaining a battery separator having excellent battery characteristics, which can be roughened and made porous at the same time.

Thus One preferred technique for roughening the battery separator surface, there is a method of using the roughening agent, in the present invention, using a method utilizing the β crystal of the polypropylene resin It is . Next, a method of using β crystals of polypropylene resin will be described.

Utilizing the β crystal of the polypropylene resin, a polypropylene resin is a shall which have a β activity. The β activity is preferably 20% or more, more preferably 40% or more, and further preferably 60% or more. When the β activity is 20% or more, the ratio of β crystals in the unstretched film can be sufficiently increased. When stretched, many fine and uniform pores are formed at the same time as the surface is formed. As a result, a battery separator having high mechanical strength, excellent air permeability, and improved battery characteristics can be obtained.

The presence or absence of the β activity is determined by performing differential thermal analysis of the battery separator using a differential scanning calorimeter and determining whether or not the crystal melting peak temperature derived from the β crystal of the polypropylene resin is detected. Yes.
Specifically, the battery separator is heated at a scanning temperature of 10 ° C./min from 25 ° C. to 240 ° C. for 1 minute with a differential scanning calorimeter, and then the scanning speed is 10 ° C./min from 240 ° C. to 25 ° C. Was held for 1 minute after cooling down, and when the temperature was raised again from 25 ° C. to 240 ° C. at a scanning rate of 10 ° C./min, a crystal melting peak temperature (Tmβ) derived from β crystals of polypropylene resin was detected. In the case, it is determined to have β activity.

The β activity, which is an index of the degree of β activity, is expressed by the following formula using the crystal heat of fusion (ΔHmα) derived from the α crystal of the polypropylene resin and the crystal heat of heat (ΔHmβ) derived from the β crystal. Calculated.
β activity (%) = [ΔHmβ / (ΔHmβ + ΔHmα)] × 100
For example, in the case of homopolypropylene, the heat of crystal melting derived from β crystal (ΔHmβ) mainly detected in the range of 145 to 160 ° C., and the crystal derived from α crystal mainly detected at 160 ° C. to 175 ° C. It can be calculated from the heat of fusion (ΔHmα). Further, for example, in the case of random polypropylene copolymerized with 1 to 4 mol% of ethylene, the amount of heat of crystal melting (ΔHmβ) derived from the β crystal detected mainly at 120 ° C. or more and less than 140 ° C. is mainly 140. It can be calculated from the crystal melting calorie (ΔHmα) derived from the α crystal detected in the range of from 0 ° C. to 165 ° C.

The β activity is preferably larger. Specifically, the β activity is preferably 20% or more, more preferably 40% or more, and particularly preferably 60% or more. If the β activity is 20% or more, it indicates that a large amount of β crystals of the polypropylene resin composition can be formed even in the film-like material before stretching, and a lot of fine and uniform holes are formed by stretching. As a battery separator having high mechanical strength and excellent air permeability.
The upper limit of β activity is not particularly limited, but the higher the β activity, the more effectively it is obtained, so the closer it is to 100%, the better.

The presence or absence of the β activity can also be determined by a diffraction profile obtained by wide-angle X-ray diffraction measurement of a battery separator subjected to a specific heat treatment.
Specifically, wide-angle X-ray diffraction measurement was performed on a battery separator that had been subjected to heat treatment at 170 to 190 ° C., which is a temperature exceeding the melting point of the polypropylene resin, and was slowly cooled to produce and grow β crystals. When a diffraction peak derived from the (300) plane of β crystal is detected in the range of 2θ = 16.0 to 16.5 °, it is determined that there is β activity.
For details on the β crystal structure and wide-angle X-ray diffraction measurement of polypropylene resins, see Macromol. Chem. 187, 643-652 (1986), Prog. Polym. Sci. Vol. 16, 361-404 (1991), Macromol. Symp. 89, 499-511 (1995), Macromol. Chem. 75, 134 (1964), and references cited therein. A detailed evaluation method of β activity will be described in Examples described later.

  As a method for obtaining the above β activity, a method of molding a molten polypropylene resin with a high draft, a method of not adding a substance that promotes the formation of α crystals of the polypropylene resin, and a method described in Japanese Patent No. 3739481 Examples thereof include a method of adding a polypropylene-based resin that has been subjected to a treatment for generating peroxide radicals, and a method of adding a β crystal nucleating agent to the resin composition. Among them, it is preferable to obtain a β activity by adding a β crystal nucleating agent to the resin composition. By adding a β crystal nucleating agent, it is possible to promote the generation of β crystals of the polypropylene resin more uniformly and efficiently, and a battery separator having a layer having β activity can be obtained.

<Β crystal nucleating agent>
Examples of the β crystal nucleating agent in the present invention include those shown below, but the β crystal nucleating agent is not particularly limited as long as it increases the β activity of polypropylene, and a mixture of two or more types is used. Also good. Examples of the β crystal nucleating agent include, for example, iron oxide having a nanoscale size; alkali or alkaline earth of carboxylic acid represented by potassium 1,2-hydroxystearate, magnesium benzoate, magnesium succinate, magnesium phthalate and the like. Metal salts; aromatic sulfonic acid compounds represented by sodium benzenesulfonate, sodium naphthalenesulfonate, etc .; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine pigments represented by phthalocyanine blue; Examples thereof include a two-component compound composed of component A which is a basic acid and component B which is an oxide, hydroxide or salt of a Group IIA metal of the periodic table. In addition, specific types of nucleating agents are described in JP-A No. 2003-306585, JP-A Nos. 06-228966, and JP-A Nos. 09-194650. Of these, amide compounds represented by N, N′-dicyclohexyl-2,6-naphthalenedicarboxylic acid amide are preferred.

  Specific examples of these particularly preferred β-crystal nucleating agents include β-nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd., and specific examples of polypropylene resins to which β-crystal nucleating agents are added include polypropylene “ Bepol B-022SP ”, Brealis polypropylene“ Beta (β) -PP BE60-7032 ”, Mayzo polypropylene“ BNX BETAPP-LN ”and the like.

  In the present invention, the ratio of the β crystal nucleating agent to be added to the polypropylene resin needs to be appropriately adjusted depending on the composition of the β crystal nucleating agent and the polypropylene resin. The β crystal nucleating agent is preferably 0.0001 to 5.0 parts by mass, more preferably 0.001 to 3.0 parts by mass, and still more preferably 0.01 to 1.0 parts by mass. By setting it to 0.0001 parts by mass or more, sufficient β activity can be ensured, and when a battery separator is obtained, desired air permeability and mechanical strength are easily exhibited. On the other hand, addition of 5.0 parts by mass or less is preferable because the β crystal nucleating agent can be sufficiently inhibited from being spread on the surface of the battery separator.

In order to ensure the safety of the battery, a porous layer (hereinafter referred to as B layer) having a shutdown function (SD function) is added to the A layer and laminated .

(B layer)
Specifically, the thermoplastic resin used for the B layer of the present invention preferably has a crystal melting peak temperature of 100 to 150 ° C. This crystal melting peak temperature is the DSC crystal melting temperature collected at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC-7) manufactured by PerkinElmer in accordance with JIS K7121. It is a peak value. The resin is not particularly limited as long as the crystal melting peak temperature condition is satisfied. Among them, when considering use as a battery separator, low-density polyethylene is used from the viewpoint of its chemical resistance. Polyolefin resins such as high density polyethylene, linear low density polyethylene, ethylene vinyl acetate copolymer, polypropylene and polymethylpentene, particularly polyethylene resins are preferred.

  The polyethylene-based resin in the present invention is a low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, and a copolymer mainly composed of ethylene, that is, ethylene and propylene, butene. -1, pentene-1, hexene-1, heptene-1, octene-1, etc., α-olefins having 3 to 10 carbon atoms; vinyl esters such as vinyl acetate and vinyl propionate; methyl acrylate, ethyl acrylate, methacryl A copolymer or multi-component copolymer with one or two or more comonomers selected from unsaturated carboxylic acid esters such as methyl acrylate and ethyl methacrylate, and unsaturated compounds such as conjugated and non-conjugated dienes, or The mixed composition is mentioned. The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these polyethylene resins, at least one polyethylene resin selected from low density polyethylene, linear low density polyethylene, and high density polyethylene is preferable, and high density polyethylene is most preferable.

  The melt flow rate (MFR) of the polyethylene resin is not particularly limited, but usually the MFR is preferably 0.03 to 15 g / 10 min, and preferably 0.3 to 10 g / 10 min. preferable. If the MFR is in the above range, the back pressure of the extruder does not become too high during the molding process and the productivity is excellent. The MFR in the present invention is a value measured under conditions of a temperature of 190 ° C. and a load of 2.16 kg in accordance with JIS K7210.

  The production method of the polyethylene resin is not particularly limited, and is a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. A polymerization method using a single site catalyst may be mentioned.

  Further, the B layer may contain other resins, other additives, or other components as long as the characteristics of the battery separator are not impaired. The additive is not particularly limited, but recycled resin generated from trimming loss such as ears, inorganic particles such as silica, talc, kaolin and calcium carbide, pigments such as titanium oxide and carbon black, flame retardants, Weather resistance stabilizer, antistatic agent, crosslinking agent, lubricant, plasticizer, anti-aging agent, antioxidant, light stabilizer, UV absorber, neutralizer, antifogging agent, antiblocking agent, slip agent, crystal nucleus Additives such as agents, waxes, or colorants.

<Layer structure>
The configuration of the battery separator of the present invention will be described.
From the viewpoint of improving battery performance, a porous layer (hereinafter abbreviated as “A layer”) having a polyolefin resin as a main component and a roughened polypropylene resin , as mentioned above, from the safety of the battery. A laminated structure composed of the B layer is employed .
Regarding the number of stacked layers, the simplest structure is a two-layer structure of A layer and B layer. Next, a simple structure is a two-layer / three-layer structure of both outer layers and middle layers, which are preferable configurations. In the case of two types and three layers, it may be A layer / B layer / A layer or B layer / A layer / B layer. In addition, it is possible to adopt a form of three types and three layers in combination with layers having other functions as required. Further, when function is added, the number of layers may be increased as necessary, such as 4, 5, 6, and 7. Among them, the layer configuration is A layer / B layer, but considering the properties of the battery separator, etc., a symmetrical layer configuration is preferable, and from this point of view, it is the form of A layer / B layer / A layer. .

<Manufacturing method>
Next, although an example is demonstrated about the manufacturing method of the battery separator of this invention, this invention is not limited only to this example. The shape of the battery separator may be either a flat shape or a tube shape. However, productivity (a few products can be taken in the width direction of the battery separator) and the inner surface can be coated. From the above, a planar shape is more preferable.

  As a production method in the case of a flat shape, for example, the resin is melted using an extruder, extruded from a T-die, cooled and solidified with a cast roll, roll-stretched in the vertical direction, tenter-stretched in the horizontal direction, and then A method for producing a battery separator stretched in the biaxial direction through steps such as annealing and cooling can be exemplified. Moreover, the method of cutting open the battery separator manufactured by the tubular method and making it planar can also be applied.

As an example, a simple case of two types and three layers will be described. As a manufacturing method, a method of laminating a previously porous film, a method of laminating with an adhesive or the like, a method of laminating a nonporous film-like material after laminating, or after directly producing a laminated nonporous film-like material by coextrusion Although there is a method of making it porous, in the present invention, co-extrusion is performed from the viewpoint of simplicity of the process and productivity.

In addition, a stretching method is also used as a porosity forming method from an environmental viewpoint, and in some cases, it may be combined with a solvent extraction method. Japanese Patent No. 3050021 can be exemplified as the solvent extraction method. For stretching method, in view of the multi-hole viewpoint of structure control and arithmetic mean roughness Ra, Ra1 / Ra2, and biaxially stretched.

Here, to form the A layer with a resin composition composed mainly of a reportage polypropylene-based resin having a β activity, and as the B layer, and formed of a resin composition composed mainly of a polyethylene resin, A film-like material laminated by a T-die coextrusion method in a two-type three-layer structure so that the A layer becomes an outer layer is made porous by using a biaxial stretching method, and will be described below.

(Preparation of resin composition for layer A)
Case of preparing the resin composition of the layer A, that use a polypropylene resin and β-crystal nucleating agent mentioned above. The resin and the β crystal nucleating agent are preferably mixed using a Henschel mixer, a super mixer, a tumbler mixer, or the like, or the whole composition is put into a bag and mixed by hand blending , and then a twin screw extruder is used. Use and melt-knead, then pelletize.

(Preparation of B layer resin composition)
When preparing the resin composition of the B layer, for example, a polyethylene resin as a thermoplastic resin and, if necessary, additives and the like are mixed using a Henschel mixer, a super mixer, a tumbler mixer, etc. , and then twin screw extrusion after melting the kneading in the machine and pelletized.

(About laminated coextrusion and stretching)
The pellets of various resin compositions of the A layer and the B layer are put into each extruder and extruded from a die for T-die coextrusion. The type of the T die may be a multi-manifold type or a feed block type.

  The gap of the T die to be used is finally determined from the required separator thickness, stretching conditions, draft rate, various conditions, etc., but generally about 0.1 to 3.0 mm is preferable and more preferable. Is 0.5 to 1.0 mm. If it is less than 0.1 mm, it is not preferable from the viewpoint of production speed, and if it is more than 3.0 mm, it is not preferable from the viewpoint of production stability because the draft rate increases.

  In extrusion molding, the extrusion temperature is appropriately adjusted depending on the flow characteristics and moldability of the resin composition, but is generally preferably 150 to 300 ° C, more preferably 180 to 280 ° C, and still more preferably 200 to 280 ° C. It is. When the temperature is 150 ° C. or higher, the viscosity of the molten resin is sufficiently low, and is excellent in moldability. On the other hand, at 300 ° C. or lower, the deterioration of the resin composition can be suppressed. The cooling and solidification temperature by the cast roll is very important in the present invention, and the ratio of β crystals in the film can be adjusted. The cooling and solidifying temperature of the cast roll is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, still more preferably 100 ° C. or higher, and particularly preferably 120 ° C. or higher. On the other hand, the lower limit is preferably 150 ° C. or lower, more preferably 140 ° C. or lower, and further preferably 130 ° C. or lower. By setting the cooling and solidification temperature to 80 ° C. or higher, the ratio of β crystals in the film-like material that has been cooled and solidified can be sufficiently increased. On the other hand, it is preferable to set the cooling and solidification temperature to less than 150 ° C. because troubles such as the extruded molten resin sticking to the cast roll and wrapping are unlikely to occur, and the film can be efficiently formed into a film.

In the stretching step, it is a biaxially oriented. Further, the biaxial extension Shin may be a simultaneous biaxial stretching may be sequential biaxial stretching. In the case of producing a separator excellent in SD characteristics and BD characteristics, which is the object of the present invention, sequential biaxial stretching is more preferable because stretching conditions can be selected in each stretching step and the porous structure can be easily controlled.

When using sequential biaxial stretching, the stretching temperature needs to be changed as appropriate depending on the composition of the resin composition to be used, the crystal melting peak temperature, the crystallinity, etc., but the stretching temperature in the longitudinal stretching is preferably about 20 to 130 ° C. More preferably, it is controlled in the range of 40 to 120 ° C, and more preferably 60 to 110 ° C. The longitudinal draw ratio is preferably 2 to 10 times, more preferably 3 to 8 times, still more preferably 4 to 7 times. By performing longitudinal stretching within the above range, it is possible to develop an appropriate pore starting point while suppressing breakage during stretching. When carrying out the longitudinal stretching, it may be stretched in a single stage at a constant temperature or may be stretched at different temperatures in multiple stages.
On the other hand, the stretching temperature in transverse stretching is generally 80 to 160 ° C, preferably 90 to 150 ° C, and more preferably 100 to 140 ° C. Further, the transverse draw ratio is preferably 1.1 times or more, more preferably 1.2 times or more, and still more preferably 1.5 times or more. On the other hand, the upper limit is preferably 10 times or less, more preferably 8 times or less, and still more preferably 7 times or less. By transversely stretching within the above range, the pore starting point formed by longitudinal stretching can be appropriately expanded, and a fine porous structure can be expressed.
The stretching speed in the stretching step is preferably 500 to 12000% / min, more preferably 1500 to 10,000% / min, and further preferably 2500 to 8000% / min.

  The biaxially stretched film thus obtained is subjected to a heat treatment at a temperature of about 130 to 170 ° C. for the purpose of improving dimensional stability, etc., and then cooled uniformly and wound up, whereby the battery of the present invention. Separator. At this time, a relaxation treatment of 3 to 20% may be performed as necessary during the heat treatment step. The thermal dimensional stability of the battery separator is further improved by the heat treatment.

  The physical properties of the battery separator of the present invention can be freely adjusted by the type of resin, the type of filler selected, the type of plasticizer, the amount and composition ratio, and stretching conditions (stretching ratio, stretching temperature, etc.). In particular, regarding the surface roughness of the polypropylene resin layer of the outer layer, when using a roughening agent, depending on the amount and type thereof, the type of plasticizer and its stretching conditions, and when using β crystals, β It can be freely adjusted depending on the amount and type of the nucleating agent, the type of plasticizer and the stretching conditions.

(Thickness and layer ratio)
The thickness of the battery separator of the present invention is preferably 5 to 50 μm. More preferably, it is 8-40 micrometers, More preferably, it is 10-30 micrometers. When used as a battery separator, if it is less than 5 μm, a large force is applied to the protruding portion of the electrode, which may break through the battery separator and cause a short circuit. Moreover, since electrical resistance will become large when thickness becomes thicker than 50 micrometers, since the performance of a battery will become inadequate, it is unpreferable.

About the lamination | stacking ratio of A layer and B layer, 10 to 90% of the ratio of A layer with respect to the total lamination thickness is preferable, More preferably, it is 15 to 85%, More preferably, it is 20 to 80%. When the ratio of the A layer is 10% or more, the BD characteristics and strength of the A layer can be sufficiently exhibited. On the other hand, when the ratio of the A layer is 90% or less, the shutdown function can be sufficiently exhibited, and safety can be ensured.
Moreover, when other layers other than A layer and B layer exist, 0.05-0.5 are preferable with respect to the total thickness 1 of the other layers, and 0.1-0. 3 is more preferable.

(Gurre value)
The Gurley value represents the difficulty in passing through the air in the film thickness direction, and is expressed as the number of seconds required for 100 ml of air to pass through the film. Means difficult. That is, a smaller value means better communication in the thickness direction of the film, and a larger value means lower communication in the thickness direction of the film. Communication is the degree of connection of holes in the film thickness direction. If the Gurley value of the battery separator of the present invention is low, it can be used for various applications. For example, when used as a battery separator for a non-aqueous lithium secondary battery, a low Gurley value means that lithium ions can be easily transferred and is preferable because of excellent battery performance. The Gurley value of the battery separator of the present invention is preferably 10 to 1000 seconds / 100 ml. More preferably, it is 15-800 seconds / 100 ml, More preferably, it is 20-500 seconds / 100 ml. If the Gurley value is 1000 seconds / 100 ml or less, the electrical resistance is substantially low, which is preferable as a battery separator. On the other hand, a Gurley value of 10 seconds / 100 ml or more is preferable because troubles such as an internal short circuit can be avoided when used as a battery separator.

(Puncture strength)
For battery separators, the piercing strength greatly contributes to short-circuiting and productivity during battery production. A method for measuring the piercing strength will be described later, but the value is preferably 1.5 N or more, more preferably 2.0 N or more, and further preferably 3.0 N or more, regardless of the thickness. If the puncture strength is lower than 1.5N, the probability of occurrence of a short circuit due to the breakage of the battery separator due to foreign matter or the like during battery production is increased, which is not preferable.

(Arithmetic mean roughness Ra)
It is important that the battery separator of the present invention has an arithmetic average roughness Ra of 0.3 μm or more, preferably 0.35 μm or more.
As a result of producing a battery using the battery separator of the present invention, there is a difference in the cycle characteristics of the battery due to the calculated average roughness Ra of the battery separator, especially when the arithmetic average roughness Ra is 0.3 μm or more. I discovered that it was important. Although details are still unclear, when the Ra is 0.3 μm or more, the portion where the electrolyte accumulates on the surface of the battery separator increases, that is, the liquid retention of the electrolyte of the battery separator is improved. This is thought to have greatly contributed to the improvement of cycle characteristics.
On the other hand, the upper limit is not particularly limited, but is preferably 0.8 μm or less. When Ra is 0.8 μm or less, it is particularly preferable when it is used as a thin battery separator that sufficiently retains the liquid retaining property of the electrolyte and requires thickness accuracy.

As an example of means for making the Ra 0.3 μm or more, it can be mentioned from both the raw material formulation and the production method.
In the raw material blending, the means varies depending on the method of expressing the surface roughness. When a roughening agent is used, the particle size and amount of the roughening agent are the main points that express the roughness. If the particle size of the surface roughening agent is too small, the effect of the surface roughening becomes thin, and if it is too large, unnecessary voids frequently occur. The grain size of the roughening agent is preferably, for example, about 0.1 to 50 μm, more preferably 0.3 to 10 μm, still more preferably 0.5 to 5 μm. Regarding the addition amount of the roughening agent, if the addition amount is too small, the effect of the roughening becomes thin, and if it is too large, the moldability of the battery separator is impaired. Usually, 1 to 70% by mass of the battery separator is preferable, and about 5 to 50% by mass is more preferable.
When β crystals are used, the type and amount of the crystal nucleating agent are related. Since the surface roughness is related to the expression level of the β crystal, it contributes to the β activity. The higher the β activity, the higher the surface roughness. More specifically, if there is a β crystal part in the film-like material, the β crystal part is depressed, and by performing stretching, the depressed parts interfere with each other and are bonded to each other. This is because fibril-like irregularities in which the shapes are intertwined in a complicated manner are generated. Thereby, the roughness of the battery separator surface of this invention is securable.
On the other hand, in the production method, the cooling and solidification temperature of the cast roll is preferably 80 ° C. or higher, more preferably 90 ° C. or higher, still more preferably 100 ° C. or higher, and particularly preferably 120 ° C. or higher. By setting the cooling and solidification temperature to 80 ° C. or higher, the ratio of β crystals in the cooled and solidified film can be sufficiently increased, and it is preferable because unevenness is generated on the surface by stretching.
Moreover , biaxial stretching is performed about extending | stretching . In particular, the transverse draw ratio is preferably 1.1 times or more, more preferably 1.2 times or more, and still more preferably 1.5 times or more. On the other hand, the upper limit is preferably 10 times or less, more preferably 8 times or less, and still more preferably 7 times or less. By subjecting to lateral stretching, the surface becomes more rough and the arithmetic average roughness Ra can be easily satisfied to 0.3 μm or more.

_(Ra 1 / _Ra 2)
Regarding the arithmetic average roughness Ra of the battery separator of the present invention, the arithmetic average roughness Ra is 0.3 μm or more, and the arithmetic average roughness Ra _{1 in} the longitudinal direction of the battery separator on both surfaces of the battery separator, It is important that the ratio Ra ₁ / Ra ₂ composed of the arithmetic average roughness Ra ₂ in the width direction is 0.80 to 1.20. Preferably it is 0.85-1.20, More preferably, it is 0.85-1.15. The arithmetic average roughness ratio Ra ₁ / Ra ₂ is considered to be an index of how the roughness is directional.
As a result of producing a battery using the battery separator of the present invention, the calculated average roughness Ra of the battery separator is 0.3 μm or more and Ra ₁ / Ra ₂ is within the specified range. It was discovered that there was a difference in characteristics, and in particular, it was discovered that Ra ₁ / Ra ₂ was 0.80 to 1.2. Although details are still unclear, when the Ra is 0.3 μm or more, the portion where the electrolyte accumulates on the surface of the battery separator increases, and if the Ra ₁ / Ra ₂ is within the specified range, the roughness is reduced. The directionality is small, that is, the part where the electrolyte is accumulated is isotropic, that is, there is little unevenness in the electrolyte retention within the battery separator surface, which greatly contributed to the improvement of the cycle characteristics of the battery it is conceivable that.

(BD characteristics)
The greatest feature of the battery separator of the present invention is that the polypropylene resin used in the A layer has high heat resistance, which is a characteristic that contributes to safety. The heat resistance is a function (breakdown characteristic) that separates the positive and negative electrodes so that the battery separator prevents direct contact between the positive and negative electrodes up to a higher temperature (160 ° C. or higher), and is a higher temperature. Is preferred. When used as a battery separator, a battery separator having this heat resistance is required.

(Non-aqueous lithium secondary battery)
A non-aqueous lithium secondary battery using the battery separator of the present invention includes a positive electrode capable of inserting and extracting lithium ions, a negative electrode capable of inserting and extracting lithium ions, a non-aqueous solvent and a lithium salt containing a lithium salt It can be set as a non-aqueous lithium secondary battery provided with electrolyte and the battery separator of the above-mentioned this invention. The non-aqueous electrolyte may be a liquid, a solid electrolyte, or a gel electrolyte. Hereinafter, the nonaqueous electrolyte other than the battery separator, the positive electrode, and the negative electrode will be described.

{Nonaqueous electrolyte}
<Non-aqueous solvent>
As the nonaqueous solvent for the electrolyte used in the nonaqueous lithium secondary battery of the present invention, any known solvent can be used as the solvent for the nonaqueous lithium secondary battery. For example, cyclic carbonates such as alkylene carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate (preferably alkylene carbonates having 3 to 5 carbon atoms); dialkyls such as dimethyl carbonate, diethyl carbonate, di-n-propylene carbonate and ethyl methyl carbonate Chain carbonates such as carbonates (preferably dialkyl carbonates having an alkyl group having 1 to 4 carbon atoms); cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; chain ethers such as dimethoxyethane and dimethoxymethane; γ-butyrolactone, γ -Cyclic carboxylic acid esters such as valerolactone; and chain carboxylic acid esters such as methyl acetate, methyl propionate, and ethyl propionate. These may be used alone or in combination of two or more.

Among the above exemplified solvents, a mixed non-aqueous solvent in which a cyclic carbonate and a chain carbonate are mixed is preferable from the viewpoint of improving overall battery performance such as charge / discharge characteristics and battery life. The mixed non-aqueous solvent contains cyclic carbonate and chain carbonate in an amount of 15% by volume or more of the whole non-aqueous solvent, and the total of these volumes is 70% by volume or more of the whole non-aqueous solvent. It is preferable to do.
As the cyclic carbonate used in the mixed non-aqueous solvent in which the cyclic carbonate and the chain carbonate are mixed, an alkylene carbonate having 2 to 4 carbon atoms in the alkylene group is preferable. Specific examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate and the like. Of these, ethylene carbonate and propylene carbonate are preferable.

Moreover, as a chain carbonate used for the mixed non-aqueous solvent which mixed said cyclic carbonate and chain carbonate, the dialkyl carbonate which has a C1-C4 alkyl group is preferable. Specific examples thereof include dimethyl carbonate, diethyl carbonate, di-n-propylene carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate and the like. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.
Each of these cyclic carbonates and chain carbonates may be used independently, or a plurality of types may be used in any combination and ratio.

The ratio of the cyclic carbonate in the mixed non-aqueous solvent is 15% by volume or more, particularly 20 to 50% by volume, and the ratio of the chain carbonate is 30% by volume or more, particularly 40 to 80% by volume. It is preferably 1: 1 to 4 (volume ratio).
Furthermore, the mixed non-aqueous solvent may contain a solvent other than the cyclic carbonate and the chain carbonate as long as the battery performance of the produced non-aqueous lithium secondary battery is not deteriorated. The ratio of the solvent other than the cyclic carbonate and the chain carbonate in the mixed non-aqueous solvent is usually 30% by volume or less, preferably 10% by volume or less.

<Lithium salt>
Any lithium salt that is a solute of the non-aqueous electrolyte can be used. For example, inorganic lithium salts 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 ₂ (C ₂ F ₅ SO ₂ ) _2, etc. Examples include lithium salts. Of these, fluorine-containing organic lithium salts such as LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (C ₂ F ₅ SO ₂ ) ₂ , particularly LiPF ₆ and LiBF ₄ are preferable. . In addition, 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 the non-aqueous electrolyte of the lithium salt, usually 0.5 mol / dm ³ or more and preferably 0.75 mol / dm ³ or more, the upper limit value, typically 2 mol / dm ³ or less, preferably 1. 5 mol / dm ³ or less. When the concentration of the lithium salt exceeds this upper limit value, the viscosity of the non-aqueous electrolyte increases and the electrical conductivity also decreases. Moreover, since electrical conductivity will become low if less than a lower limit, it is preferable to prepare a non-aqueous electrolyte in the said density | concentration range.

<Other additives>
The non-aqueous electrolyte according to the present invention may contain a film forming agent capable of forming a resistive film on the negative electrode surface. As the film forming agent used in the present invention, carbonate compounds having ethylenically unsaturated bonds such as vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, erythritan carbonate, succinic anhydride, Carboxylic anhydride such as glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride Thing etc. are mentioned. In particular, from the viewpoint of good cycle characteristics improvement effect and temperature dependency of film resistance, vinylene carbonate, vinyl ethylene carbonate, and succinic anhydride are preferable as the film forming agent, and a particularly good film can be formed. More preferably, vinylene carbonate is used. In addition, these film formation agents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

  In the present invention, the content of the film forming agent in the non-aqueous electrolyte is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and 10% by mass or less. Preferably it is 8 mass% or less, More preferably, it is 7 mass% or less. If the content of the film forming agent is below the lower limit of the above range, it is difficult to obtain the effect of improving the cycle characteristics of the battery. On the other hand, if the content exceeds the upper limit, the rate characteristics at low temperatures may be lowered.

  In addition to the non-aqueous solvent, the lithium salt and the film forming agent, the non-aqueous electrolyte according to the present invention includes other useful components as necessary, for example, conventionally known ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone. , Vitan sultone, methyl methanesulfonate, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, dipyridinium disulfide, etc. Various additives such as a positive electrode protective agent, an overcharge preventing agent, a dehydrating agent, and a deoxidizing agent may be contained.

{Positive electrode}
As the positive electrode, a material in which an active material layer containing a positive electrode active material and a binder is usually formed on a current collector is used.
The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Preferable examples include lithium transition metal composite oxides. Specific examples of lithium transition metal composite oxides include lithium / cobalt composite oxides such as LiCoO ₂ , lithium / nickel composite oxides such as LiNiO _2, and lithium / manganese composite oxides such as LiMnO ₂ and LiMn ₂ O _4. Is mentioned. In these lithium transition metal composite oxides, some of the main transition metal atoms are Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, etc. Replacing with other metals is preferable because it can be stabilized. Any one of these positive electrode active materials may be used alone, or two or more thereof may be used in any combination and ratio.

  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), Examples thereof include fluororubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, and nitrocellulose. 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, the lower limit is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, and the upper limit is usually 80% by mass or less, preferably 60%. It is at most 10% by mass, more preferably at most 40% by mass, even more preferably at most 10% by mass. 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 graphite fine particles such as natural graphite and artificial graphite, carbon black such as acetylene black, amorphous carbon fine particles such as needle coke, and carbonaceous materials such as carbon fiber, carbon nanotube, and fullerene. . These may be used individually by 1 type, or may use multiple types together.

  As for the ratio of the conductive agent in the positive electrode active material, the lower limit is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and the upper limit is usually 50% by mass or less. Preferably it is 30 mass% or less, More preferably, it is 15 mass% 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 carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, 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 positive electrode current collector.
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.

  Thus, the thickness of the positive electrode active material layer formed is about 10-200 micrometers normally. 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}
As the negative electrode, a material in which an active material layer containing a negative electrode active material and a binder is usually formed on a current collector is used.
The negative electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions. Preferable examples include carbonaceous materials capable of occluding and releasing lithium, such as organic pyrolysis products and 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. In particular, among the above, as the negative electrode active material used in combination with the separator of the present invention, carbonaceous materials such as artificial graphite and natural graphite, metal oxide materials, and lithium alloys improve battery characteristics such as cycle characteristics. preferable.

  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, SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber and the like. These may be used individually by 1 type, or may use multiple types together.

  As for the ratio of the binder in the negative electrode active material, the lower limit is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, and the upper limit is usually 80% by mass or less, preferably 60%. It is at most 10% by mass, more preferably at most 40% by mass, even more preferably at most 10% by mass. If the ratio of the binder is small, the active material cannot be sufficiently retained, so that the negative electrode has insufficient mechanical strength, which may deteriorate the battery performance such as cycle characteristics. It will be.

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

  Thus, the thickness of the negative electrode active material layer formed is about 10-200 micrometers normally. 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 configuration}
The non-aqueous lithium secondary battery of the present invention is manufactured by assembling the positive electrode, negative electrode, non-aqueous electrolyte, and battery separator described above into appropriate shapes. Furthermore, other components such as an outer case can be used as necessary.
The shape of the battery is not particularly limited, and can be appropriately selected from various commonly used shapes according to the application. Examples of commonly adopted shapes include a cylinder type with a sheet electrode and battery separator spiral, an inside-out cylinder type with a combination of pellet electrode and battery separator, pellet electrode and battery separator. Examples thereof include a laminated coin type, a laminated type in which a sheet electrode and a battery separator are laminated. Further, the method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

  The general embodiment of the non-aqueous lithium secondary battery of the present invention has been described above. However, the non-aqueous lithium secondary battery of the present invention is not limited to the above-described embodiment, as long as it does not exceed the gist thereof. It is possible to implement various modifications.

Next, examples and comparative examples will be shown, and the battery separator and non-aqueous lithium secondary battery of the present invention will be described in more detail. However, the present invention is not limited to these.
In addition, the measured value and evaluation which are shown to an Example and a comparative example were performed as follows. The take-up (flow) direction of the battery separator is referred to as the “vertical” direction, and the direction perpendicular thereto is referred to as the “lateral” direction.

(1) Thickness With a dial gauge of 1/1000 mm, 30 in-plane measurements are made unspecified, and the average is taken as the thickness.
(2) Layer ratio The layer ratio was measured by cutting out the cross section of the separator and observing with a scanning electron microscope.
(3) Gurley value The Gurley value (second / 100 ml) was measured according to JIS P8117.
(4) Puncture strength Measured according to Japanese Agricultural Standards Notification No. 1019. (Pin diameter: 1.0 mm, tip: 0.5 R, piercing speed: 300 mm / min)

(5) Arithmetic mean roughness Ra
It measured based on JIS B0601-1994.
A battery separator is cut out with a width of 10 mm × 50 mm. A double-sided tape (Nitto Denko's double-sided adhesive tape, No. 501F, 5 mm) in which the cut battery separator was stretched 15 mm apart and parallel to a glass plate (Matsunami Glass Industrial Co., Ltd., Microslide Glass S1225, 76 mm × 26 mm). Paste to width x 20m). At this time, due to the height of the double-sided tape, the central portion of the battery separator is fixed in a floating state without being directly attached to the glass plate.
The sample produced by the above method was measured for arithmetic average roughness Ra using a laser microscope (manufactured by Keyence Corporation, VK-8500). At this time, the range in which the arithmetic average roughness was measured was 110 μm × 150 μm, the above measurement was performed five times at different locations, and the average value of the calculated arithmetic average roughness Ra was calculated as the arithmetic average roughness Ra of the battery separator. did.

(6) Ra ₁ / Ra ₂
A sample is produced by the same method as that for the arithmetic average roughness Ra. When the arithmetic average roughness of the sample in this state is measured using a laser microscope (manufactured by Keyence Corporation; VK-8500), the longitudinal direction of the battery separator is measured at any five locations displayed on the screen. The laser was scanned linearly in each width direction, and the average value of Ra at the time of measurement was Ra ₁ and Ra ₂ , respectively, and the ratio was Ra ₁ / Ra ₂ .

(7) BD characteristics A battery separator is cut into 80 mm square. The cut-out battery separator is sandwiched between a Teflon (registered trademark) film having a hole in the center and an aluminum plate, and the periphery is fixed with a clip. The battery separator is put in a temperature oven set at 180 ° C., taken out 2 minutes after reaching the set temperature again, and the state of the battery separator is checked to determine the shape maintenance performance. When the battery separator was broken, “X” was indicated, and when the shape was maintained, “◯” was indicated. As the oven, Tabai Gear Oven GPH200 manufactured by Tabai Espec was used.

Further, the obtained battery separator was evaluated for β activity as follows.
(8) Differential scanning calorimetry (DSC)
The obtained battery separator was heated from 25 ° C. to 240 ° C. at a scanning speed of 10 ° C./min for 1 minute using a differential scanning calorimeter (DSC-7) manufactured by Perkin Elmer, and then held for 240 minutes. The temperature was lowered from 10 ° C. to 25 ° C. at a scanning speed of 10 ° C./min and held for 1 minute, and then heated again from 25 ° C. to 240 ° C. at a scanning speed of 10 ° C./min. The presence or absence of β activity was evaluated according to whether or not a peak was detected at 145 to 160 ° C., which is a crystal melting peak temperature (Tmβ) derived from the β crystal of the polypropylene resin at the time of reheating.
○: When Tmβ is detected within the range of 145 ° C to 160 ° C (with β activity)
X: When Tmβ is not detected within the range of 145 ° C to 160 ° C (no β activity)
The β activity was measured with a sample amount of 10 mg under a nitrogen atmosphere.

(9) Wide angle X-ray diffraction measurement (XRD)
A battery separator was cut into a 60 mm long × 60 mm wide square and fixed as shown in FIGS.
A sample in which the battery separator is constrained by two aluminum plates is placed in an air-cooled thermostat (Yamato Scientific Co., Ltd., model: DKN602) with a set temperature of 180 ° C and a display temperature of 180 ° C, and then set for 3 minutes The temperature was changed to 100 ° C., and the mixture was gradually cooled to 100 ° C. over 10 minutes or more. A sample was taken out when the display temperature reached 100 ° C, and the battery separator obtained by cooling for 5 minutes in an atmosphere of 25 ° C while being restrained by two aluminum plates was measured under the following measurement conditions. Wide-angle X-ray diffraction measurement was performed on a circular part of 40 mmφ of the part.
-Wide-angle X-ray diffraction measurement device: manufactured by Mac Science, model number: XMP18A
X-ray source: CuKα ray, output: 40 kV, 200 mA
Scanning method: 2θ / θ scan, 2θ range: 5 ° to 25 °, scanning interval: 0.05 °, scanning speed: 5 ° / min
About the obtained diffraction profile, the presence or absence of β activity was evaluated as follows from the peak derived from the (300) plane of β crystal of the polypropylene resin.
○: When a peak is detected in the range of 2θ = 16.0 to 16.5 ° (with β activity)
X: When no peak was detected in the range of 2θ = 16.0 to 16.5 ° (no β activity)
When the battery separator piece cannot be cut into a 60 mm × 60 mm square, a sample may be prepared by adjusting the battery separator to be installed in a circular hole of 40 mmφ in the center.

Example 1
As the A layer, polypropylene resin (manufactured by Prime Polymer Co., Ltd., 300 SV, density: 0.90 g / cm ³ , MFR: 3.0 g / 10 min, Tm: 167 ° C.) and β crystal nucleating agent, N, N ′ -Dicyclohexyl-2,6-naphthalenedicarboxylic acid amide was prepared. Each raw material is blended at a ratio of 0.2 parts by mass of β-crystal nucleating agent with respect to 100 parts by mass of this polypropylene resin, and a twin-screw extruder manufactured by Toshiba Machine Co., Ltd. (caliber: 40 mmφ, L / D: 32). ), Melted and mixed at a preset temperature of 300 ° C., cooled and solidified the strands in a water tank, cut the strands with a pelletizer, and produced polypropylene resin pellets. The β activity of the polypropylene resin composition was 80%.

Next, as a mixed resin composition constituting the B layer, glycerin is added to 100 parts by mass of high-density polyethylene (manufactured by Nippon Polytechnic Co., Ltd., Novatec HD HF560, density: 0.963 g / cm ³ , MFR: 7.0 g / 10 min). Add 0.04 parts by mass of monoester and 10 parts by mass of microcrystalline wax (Hi-Mic 1080, manufactured by Nippon Seiwa Co., Ltd.), melt and knead at 220 ° C. using the same type twin screw extruder, and pellets A resin composition processed into a shape was obtained.

Using the above-mentioned two kinds of raw materials, using a separate extruder so that the outer layer is the A layer and the intermediate layer is the B layer, it is extruded from a die for multilayer molding through a feed block of two types and three layers, at 127 ° C. The film was cooled and solidified with a casting roll to produce a laminated film.
The laminated film is stretched 4.4 times in the longitudinal direction using a longitudinal stretching machine, and then stretched 2.0 times in the lateral direction at 105 ° C. with a transverse stretching machine, followed by heat setting / relaxation treatment. A battery separator was obtained. Table 1 shows the physical properties of the obtained battery separator.

(Example 2)
The same as Example 1 except that the high-density polyethylene resin of layer B was high-density polyethylene (manufactured by Prime Polymer, Hi-ZEX3300F, density: 0.950 g / cm ³ , MFR: 1.1 g / 10 min). A laminated film was produced under the conditions.
The laminated film is stretched 4.8 times in the longitudinal direction using a longitudinal stretching machine, and then stretched 2.1 times in the lateral direction at 105 ° C. with a transverse stretching machine, followed by heat setting / relaxation treatment. A battery separator was obtained. Table 1 shows the physical properties of the obtained battery separator.

(Example 3)
A laminated film material was produced under the same conditions as in Example 1. The laminated film-like product is stretched 3.9 times in the longitudinal direction using a longitudinal stretching machine, and then stretched 1.8 times in the lateral direction at 105 ° C. with a transverse stretching machine, followed by heat setting and relaxation treatment. A battery separator was obtained. Table 1 shows the physical properties of the obtained battery separator.

(Comparative Example 1)
Polypropylene resin (Prime Polymer Co., Ltd., 300 SV, density: 0.90 g / cm ³ , MFR: 3.0 g / 10 min, Tm: 167 ° C.) as layer A, and polyethylene resin (prime polymer) as layer B 2208J, density: 0.964 g / cm ³ , MFR: 5.2 g / 10 min, Tm: 135 ° C.). Next, a laminated film obtained by co-extrusion using a die for multilayer molding so that the outer layer is an A layer and the intermediate layer is a B layer with a two-layer / three-layer structure having a draft rate of 200 Was annealed in an oven at 115 ° C.
After annealing, the film was stretched at 25 ° C. so as to be 1.5 times the length before stretching. Next, after extending | stretching at 120 degreeC so that the length after extending | stretching at 25 degreeC may be 3.2 time, heat processing was implemented so that 10% relaxation might be applied. The physical property values of the obtained battery separator are shown in Table 1.

<Preparation of non-aqueous electrolyte>
Purified ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 3: 7 in a dry argon atmosphere to prepare a mixed solvent. In the solvent, LiPF ₆ that was sufficiently dried was dissolved to a ratio of 1 mol / dm ³ to obtain a non-aqueous electrolyte.

<Preparation of positive electrode>
LiCoO ₂ is used as the positive electrode active material, and 6 parts by mass of carbon black and 9 parts by mass of polyvinylidene fluoride (trade name “KF-1000” manufactured by Kureha Chemical Co., Ltd.) are added to 85 parts by mass of LiCoO ₂ , and N-methyl- Disperse with 2-pyrrolidone to form a slurry. This was uniformly applied to both surfaces of a 20 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 3.0 g / cm ^3. It was.

<Production of negative electrode>
Natural graphite powder was used as the negative electrode active material, and 94 parts by mass of natural graphite powder was mixed with 6 parts by mass of polyvinylidene fluoride, and dispersed with N-methyl-2-pyrrolidone to form a slurry. This was uniformly applied to both sides of a 18 μm thick copper foil as a negative electrode current collector, dried, and then pressed by a press machine so that the density of the negative electrode active material layer was 1.5 g / cm ^3. It was.

<Battery assembly>
The negative electrode plate and the positive electrode plate produced as described above were rolled up together with each battery separator, and the outermost periphery was stopped with a tape to obtain a spiral electrode body. The electrode body was inserted into the stainless steel battery case formed into a cylindrical shape from the opening. After that, the negative electrode lead connected to the negative electrode of the electrode body is welded to the inner bottom portion of the battery case, and the positive electrode lead connected to the positive electrode of the electrode body is increased to a predetermined level or more when the gas pressure inside the battery rises. Welded with the bottom of the working current interrupter. In addition, an explosion-proof valve and a current interrupt device were attached to the bottom of the sealing plate. And after inject | pouring 5 ml of said electrolytes, the battery case was sealed by the sealing plate and the polypropylene-made insulating gasket at the opening part, and it was set as the non-aqueous lithium secondary battery of Example 1.

<Battery evaluation>
(1) Initial charge / discharge At 25 ° C., the charge end voltage is a constant current equivalent to 0.2 C (the rated capacity with a discharge rate of 1 hour is 1 C, the current value for discharging in 1 hour is the same), and so on. Charge and discharge for 3 cycles at 2V and end-of-discharge voltage of 3V, stabilize in the 4th cycle with a current corresponding to 0.5C to the end-of-charge voltage of 4.2V, and a current corresponding to a charge current value of 0.05C The battery was charged until the value reached 4.2 V-constant current constant voltage charge (CCCV charge) (0.05 C cut), and then 3 V discharge was performed at a constant current value corresponding to 0.2 C. The discharge capacity at this time was defined as the initial capacity. The battery thus manufactured has an initial discharge capacity of about 2000 mAh.

(2) Cycle test The cycle test was performed by charging the battery that had been subjected to the initial charge / discharge (1) up to a charge upper limit voltage of 4.2V by a constant current / constant voltage method of 0.5C, and then to a discharge end voltage of 3V. A charge / discharge cycle for discharging at a constant current of 0.5 C was defined as one cycle, and this cycle was repeated 1000 cycles. The cycle test was conducted at 25 ° C. After this cycle test, the same charge / discharge as (1) initial charge / discharge was performed, and the ratio of the final discharge capacity to the initial capacity at this time is shown in Table 2 as the cycle maintenance ratio (%).

(3) High temperature storage test (1) After charging the battery that had been initially charged and discharged at 25 ° C. with a constant current corresponding to 0.5 C to a charge end voltage of 4.2 V, the battery was charged at a constant voltage for 2.5 hours. The battery was fully charged. The battery was stored at 60 ° C. for 30 days. The battery after storage was discharged to 3 V at 25 ° C. with a current value corresponding to 0.2 C, and then charged with 4.2 V-CCCV as in the initial stage, and 3 V was discharged with a constant current corresponding to 0.2 C. It was. Table 2 shows the discharge capacity at this time as the post-storage capacity and the ratio to the initial capacity as the capacity recovery rate (%).

Table 2 shows the results of BD characteristics and battery evaluation using each battery separator.

  From Table 2, the battery separators of the examples configured within the range defined by the present invention have cycle characteristics and high-temperature storage characteristics as compared with the battery separators of comparative examples configured outside the range defined by the present invention. It can be seen that the battery characteristics such as are excellent.

  The battery separator of the present invention is particularly excellent in battery characteristics such as cycle characteristics and high-temperature storage characteristics, and therefore can be used as a battery separator for non-aqueous lithium secondary batteries.

31 Aluminum plate 32 Battery separator 33 Clip 34 Battery separator longitudinal direction 35 Battery separator width direction

Claims (4)

A laminated porous film formed by biaxially stretching a film-like product obtained by laminating a resin composition mainly composed of a polypropylene resin having β activity and another resin composition by a co-extrusion method Consists of
Porous layer mainly composed of polypropylene resin having the β activity is arranged on at least one side surface, the arithmetic mean roughness Ra of the surface is not less 0.3μm or more, the longitudinal direction of the separator in the separator both surfaces A battery separator, wherein a ratio Ra1 / Ra2 comprising the arithmetic average roughness Ra1 and the arithmetic average roughness Ra2 in the width direction is 0.80 to 1.20. The porous layer (B layer) made of the other resin composition is a layer that forms a shutdown layer at a crystal melting peak temperature of 100 to 150 ° C., and is composed mainly of the polypropylene-based resin having the β activity. Both surfaces on both sides of the B layer with a layer (A layer) is the A layer, and Ra on the both surface is 0.3 μm or more and 10 μm or less,
The battery separator according to claim 1, wherein the battery has a thickness of 5 to 50 μm, a Gurley value of 10 to 1000 seconds / 100 ml, and a puncture strength of 1.5 N or more . A nonaqueous lithium secondary battery in which the battery separator according to claim 1 or 2 is incorporated. It is a manufacturing method of the battery separator according to claim 1 or 2 ,
A film composition is formed by coextruding a resin composition mainly composed of a polypropylene resin having β activity and another resin composition while heating at 150 ° C. to 300 ° C.
A method for producing a battery separator, wherein the film-like product is biaxially stretched with a longitudinal stretching ratio of 2 to 10 times and a lateral stretching ratio of 1.1 to 10 times.

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