JP2018147769A - Separator for electrochemical element and nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: separator which is superior in safety when abnormally heated and in reliability against an internal short circuit and a short circuit owing to dendrite, and which enables the construction of an electrochemical element arranged so that the worsening of characteristics in high-temperature storage can be suppressed; and a nonaqueous electrolyte battery having the separator.SOLUTION: A separator for an electrochemical element according to the present invention comprises at least a porous layer including inorganic particles, a cellulose fiber and a binder resin. With the porous layer, when the total volume of the inorganic particles and the cellulose fiber is 100 vol.%, the content of the inorganic particles is 70-95 vol.%. In the porous layer, the content of the binder resin is 0.1-4 mass%. A nonaqueous electrolyte battery according to the invention comprises the separator for an electrochemical element of the invention.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a separator for constituting an electrochemical element that is excellent in safety and reliability at high temperatures and can suppress performance degradation during high-temperature storage, and a nonaqueous electrolyte battery having the separator.

  A non-aqueous electrolyte battery using a non-aqueous electrolyte typified by a lithium secondary battery is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density. As the performance of portable devices increases, non-aqueous electrolyte batteries tend to have higher capacities, and at the same time, ensuring safety is important.

Conventionally, lithium secondary batteries that are generally used use a lithium-cobalt composite oxide having a layered structure typified by LiCoO ₂ as a positive electrode active material, and use an amount of carbon material such as graphite or amorphous graphite as a negative electrode active material. In general, a non-aqueous electrolyte solution in which a lithium salt such as LiPF ₆ is dissolved in a carbonate ester such as ethylene carbonate or diethyl carbonate is used as an electrolyte, and a polyolefin microporous membrane is used as a separator. It was. In recent years, in order to increase the thermal stability to ensure safety, or to increase the energy density by operating at a higher potential, spinel type lithium manganese composite oxide typified by LiMn ₂ O ₄ , like layered compound represented by LiMn _q Ni _r Co _S O ₂ has been used as the positive electrode active material of a lithium secondary battery.

  However, when these composite oxides containing Mn are used for the positive electrode, the Mn ions are eluted from the positive electrode particularly at a high temperature, leading to a decrease in the capacity of the positive electrode. It is known that side reactions other than those related to charge / discharge occur due to deterioration or reaction with a non-aqueous electrolyte to generate gas.

  In order to solve these problems, attempts have been made to stabilize the active material using a substitution element and suppress metal elution such as Mn, as shown in Patent Document 1, Patent Document 2, and the like. However, the side reaction as described above cannot be completely suppressed.

  Regarding the separator of the lithium secondary battery, a polyolefin-based porous film having a thickness of, for example, about 20 to 30 μm is used between the positive electrode and the negative electrode. In addition, as separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to ensure the so-called shutdown effect, polyethylene (PE) having a low melting point may be applied.

  By the way, when such a microporous film separator is used, metal ions such as Mn eluted from the positive electrode at high temperatures may be deposited, resulting in clogging in the vicinity of the negative electrode surface, which may greatly reduce battery characteristics. High nature. Furthermore, as such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used to increase the porosity and improve the strength. Such a separator has a problem that the film is distorted by the above stretching, and shrinkage occurs due to residual stress when the film is exposed to a high temperature. When the separator becomes smaller due to the shrinkage, the positive electrode and the negative electrode are in direct contact with each other to form a short-circuit portion. When the portion becomes large, the short-circuit current increases the internal temperature of the battery, which may make the battery dangerous.

  In order to prevent such a short circuit due to heat shrinkage, a method using a microporous film or a nonwoven fabric using a heat-resistant resin as a separator has been proposed. For example, Patent Document 3 discloses a separator using a wholly aromatic polyamide microporous film, and Patent Document 4 discloses a separator using a polyimide porous film. Patent Document 5 discloses a technique related to a separator using paper (nonwoven fabric) made of cellulose as a raw material.

  Furthermore, since cellulose has a property of reducing and fixing metal ions, it is possible that metal ions eluted from the positive electrode can be trapped by the separator by using a separator made of cellulose for the battery.

  However, separators using heat-resistant resins and heat-resistant fibers as described above are excellent in dimensional stability at high temperatures, whereas high-heat-resistant resins such as wholly aromatic polyamides and polyimides are expensive and costly. It is disadvantageous in terms. Paper and non-woven fabrics made from cellulose are very inexpensive, but they are inferior in the uniformity of the pore size compared to microporous films, and the maximum pore size is large, so it is difficult to prevent short circuit due to dendrites. .

JP 2000-30709 A JP 11-339803 A JP-A-5-335005 JP 2000-306568 A JP-A-8-306352

  The present invention has been made in view of the above circumstances, and the object thereof is excellent in safety when abnormally overheating, reliability against internal short circuit and short circuit due to dendrite, and can suppress deterioration of characteristics during high temperature storage. It is providing the separator which can comprise an electrochemical element, and the nonaqueous electrolyte battery which has the said separator.

  The separator for an electrochemical element of the present invention that has achieved the above object has at least a porous layer containing inorganic particles, cellulose fibers, and a binder resin, and the inorganic particles in the porous layer and the When the total amount of cellulose fibers is 100% by volume, the content ratio of the inorganic particles is 70 to 95% by volume, and the content ratio of the binder resin in the porous layer is 0.1 to 4% by mass. It is characterized by this.

  The nonaqueous electrolyte battery of the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and has the separator for an electrochemical element of the present invention as the separator. .

  According to the present invention, it is excellent in reliability against internal short circuit and short circuit caused by dendrite, is excellent in safety when the temperature of the battery rises abnormally due to short circuit or overcharge, etc., and deteriorates characteristics during high temperature storage. The separator which can comprise the electrochemical element which can be suppressed, and the nonaqueous electrolyte battery which has the said separator can be provided.

It is a top view which represents typically an example of the nonaqueous electrolyte battery of this invention. It is the II sectional view taken on the line of FIG.

  The porous layer constituting the separator for electrochemical devices of the present invention (hereinafter simply referred to as “separator”) includes inorganic particles, cellulose fibers, and a binder resin.

  The cellulose fiber according to the porous layer has a function of increasing the strength of the separator itself, but further has a function of trapping metal ions eluted from the positive electrode active material contained in the positive electrode of the nonaqueous electrolyte battery. ing.

  When a nonaqueous electrolyte battery in a charged state is stored in a high temperature environment, metal ions are eluted from the positive electrode active material, which causes clogging in the vicinity of the negative electrode of the separator and causes deterioration of the characteristics of the battery. If so, clogging of the separator during high-temperature storage can be suppressed by the function of the cellulose fiber. Therefore, in an electrochemical element such as a non-aqueous electrolyte battery using the separator of the present invention (non-aqueous electrolyte battery of the present invention), deterioration in characteristics during high-temperature storage is satisfactorily suppressed.

  In addition, the inorganic particles related to the porous layer have a function of suppressing the occurrence of internal short circuit of the battery and short circuit due to lithium dendrite by making the separator have a dense porous structure. Therefore, in an electrochemical element such as a non-aqueous electrolyte battery using the separator of the present invention (non-aqueous electrolyte battery of the present invention), the reliability against an internal short circuit or a short circuit caused by a dendrite is improved.

  Furthermore, by forming a porous layer with inorganic particles and cellulose fibers, the heat resistance of the separator can be increased, and the shrinkage of the entire separator when the temperature inside the battery becomes high can be suppressed. It is possible to suppress a short circuit due to contact. Therefore, in an electrochemical element such as a non-aqueous electrolyte battery using the separator of the present invention (non-aqueous electrolyte battery of the present invention), safety at high temperatures is improved.

  However, when forming a porous layer with inorganic particles, cellulose fibers, and a binder resin, depending on their composition balance, the ion permeability of the separator is reduced, and it is not possible to constitute an electrochemical device with sufficient characteristics. It became clear by examination of the present inventors. Therefore, in the separator of the present invention, by optimizing the content ratios of these constituent materials, the ion permeability of the separator can be increased, and an electrochemical device having good characteristics can be configured.

  The cellulose fibers related to the porous layer include fibers composed of cellulose derivatives in addition to fibers composed of cellulose. Specific examples of cellulose constituting the cellulose fiber include cellulose such as natural cellulose and synthetic cellulose such as rayon; and cellulose derivatives such as hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose.

  The average fiber diameter of the cellulose fibers is preferably 0.05 μm or less from the viewpoint of increasing the surface area of the cellulose fibers and further enhancing the function of trapping metal ions eluted from the positive electrode active material, and is 0.03 μm or less. More preferably. However, if the cellulose fiber is too thin, it may be difficult to manufacture the separator and to manufacture and handle the cellulose fiber itself. Therefore, the average fiber diameter of the cellulose fibers is preferably 0.005 μm or more, and more preferably 0.01 μm or more.

  Moreover, it is preferable that the average fiber length of a cellulose fiber is 0.1-5.0 micrometers.

  The average fiber diameter and the average fiber length of the cellulose fiber referred to in this specification are obtained by taking a scanning electron microscope (SEM) photograph of the fiber, drawing a line at an arbitrary position on the photograph, and crossing the line. It is a value obtained by counting the fiber diameter and the fiber length (each n = 20 or more) and calculating the average value (number average) thereof.

Examples Specific examples of the constituent material of the inorganic particles according to the porous layer is electrochemically stable, and may be any as long as electrical insulation, for example, iron oxide _{(Fe x O y; FeO,} Fe 2 O ₃ etc.), SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₂ , ZrO ₂ and other inorganic oxides; aluminum nitride, silicon nitride and other inorganic nitrides; calcium fluoride, fluoride Examples include slightly soluble ionic crystals such as barium, barium sulfate, and calcium carbonate; covalent bonds such as silicon and diamond; and clays such as montmorillonite. Here, the inorganic oxide may be a mineral resource-derived substance such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or an artificial product thereof. In addition, the surface of a conductive material exemplified by metal, SnO ₂ , conductive oxide such as tin-indium oxide (ITO), carbonaceous material such as carbon black, graphite, etc., is a material having electrical insulation ( For example, the particle | grains which gave the electrical insulation property by coat | covering with the said inorganic oxide etc. may be sufficient. Among the inorganic particles, particles composed of any of alumina, silica, kaolin, barium sulfate, and boehmite are preferable.

  As the inorganic particles, only one kind of particles composed of the above-described constituent materials may be used, or two or more kinds of particles may be used.

  The shape of the inorganic particles may be, for example, a shape close to a sphere or may be a plate shape, but from the viewpoint of further improving the short-circuit preventing function, a plate-like particle is preferable. Typical examples of the plate-like particles include plate-like alumina and plate-like boehmite. In addition, primary particles may be used as the inorganic particles, or secondary particles in which the primary particles are aggregated may be used.

  The particle diameter of the inorganic particles is an average particle diameter, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 15 μm or less, and 5 μm or less. Is more preferable.

  The average particle diameter of the inorganic particles referred to in the present specification is, for example, a number average particle diameter measured by dispersing them in a medium that does not dissolve them using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). (The average particle diameter described in the examples below is a value measured by this method).

  Examples of the binder resin related to the porous layer include ethylene-acrylic acid such as ethylene-vinyl acetate copolymer (EVA, having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-ethyl acrylate copolymer, and the like. Copolymer, fluorinated rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane An epoxy resin can be used, and a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is particularly preferably used. As the binder resin, those exemplified above may be used singly or in combination of two or more.

  Among the binder resins exemplified above, those having high flexibility such as EVA, ethylene-acrylic acid copolymer, fluorine rubber, and SBR are preferable. Specific examples of such highly flexible binder resins include “Evaflex Series (EVA)” by Mitsui DuPont Polychemical Co., Ltd., EVA by Nihon Unicar Co., Ltd. -Acrylic acid copolymer) ", Nippon Unicar's EEA, Daikin Industries'" Daiel Latex Series (Fluororubber) ", JSR's" TRD-2001 (SBR) ", Nippon Zeon's" EM-400B " (SBR) ".

  In the porous layer, the ratio of the inorganic particles when the total of the inorganic particles and the cellulose fibers is 100% by volume improves the ion permeability of the separator so that the separator can be used in an electrical device such as a non-aqueous electrolyte battery. From the viewpoint of enhancing the characteristics of the chemical element, it is 70% by volume or more. That is, the ratio of the cellulose fiber when the total of the inorganic particles and the cellulose fiber is 100% by volume is 30% by volume or less, and from the viewpoint of adjusting the air permeability, it is preferably 20% by volume or less. .

  Further, from the viewpoint of favorably securing the above-described action (giving strength to the separator) by using cellulose fibers, the ratio of the inorganic particles when the total of the inorganic particles and the cellulose fibers is 100% by volume is 95 volumes. % Or less, and preferably 90% by volume or less. That is, the ratio of the cellulose fiber when the total of the inorganic particles and the cellulose fiber is 100% by volume is 5% by volume or more, and preferably 10% by volume or more.

  In addition, from the viewpoint of favorably securing the action of trapping metal ions eluted from the positive electrode active material due to the use of cellulose fibers, similarly, the cellulose fibers when the total of the inorganic particles and the cellulose fibers is 100% by volume. The ratio may be 5% by volume or more.

  Furthermore, in the porous layer, the content ratio of the binder resin is 4% by mass or less from the viewpoint of improving the characteristics of an electrochemical element such as a non-aqueous electrolyte battery in which the separator has good ion permeability and the separator is used. It is preferable that it is 3 mass% or less. In the porous layer, from the viewpoint of satisfactorily binding inorganic particles and cellulose fibers, the binder resin content in the porous layer is 0.1% by mass or more, and 0.5% by mass or more. Preferably there is.

  The porous layer may contain components other than inorganic particles, cellulose fibers, and binder resins (resin particles, resin fibers other than cellulose fibers, etc.) as long as the effects of the present invention are not impaired.

  Further, the separator can have a single layer structure composed only of a porous layer containing inorganic particles, cellulose fibers and a binder resin, and if necessary, a porous layer containing inorganic particles, cellulose fibers and a binder resin; A multi-layer structure (two-layer structure, three-layer structure, etc.) having other layers can also be used.

  When the separator has a multilayer structure, for example, it is made of polyolefin (polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, etc.) separately from the porous layer containing inorganic particles, cellulose fibers, and a binder resin. By having a layer made of a porous film such as a microporous film, non-woven fabric, or polyolefin particle coating film, when the inside of the battery becomes abnormally hot, the pores are closed and the electrochemical reaction proceeds A shutdown function can be ensured.

  When the separator has a multilayer structure, in the porous layer containing inorganic particles, cellulose fibers and binder resin, the ratio of inorganic particles in the total of inorganic particles and cellulose fibers (ratio of cellulose fibers), binder resin It is only necessary for the content ratio of to satisfy the above value.

  The thickness of the separator (including the case of the multilayer structure described above, unless otherwise specified) is preferably 5 to 30 μm.

  In the case where the separator has a multilayer structure, the thickness of the porous layer containing inorganic particles, cellulose fibers and binder resin is preferably 1 μm or more. It is desirable to set within the range to satisfy.

  The separator preferably has an air permeability represented by a Gurley value specified in JIS P 8117 of 1000 sec / 100 ml or less, and more preferably 500 sec / 100 ml or less. If the separator has such an air permeability, since the ion permeability is good, the characteristics of an electrochemical element such as a non-aqueous electrolyte battery can be improved. However, if the air permeability of the separator is too small, the effect of suppressing fine short-circuiting by lithium dendrite may be reduced. Therefore, it is preferably 50 sec / 100 ml or more, and more preferably 80 sec / 100 ml or more.

  In the case of a single-layer structure separator, the air permeability of the separator is adjusted to the above-mentioned preferred value by adopting the separator structure described so far (the structure of the porous layer containing inorganic particles, cellulose fibers, and a binder resin). can do. On the other hand, in the case of a separator having a multilayer structure, it is preferable that the layers other than the porous layer containing inorganic particles, cellulose fibers, and a binder resin have a configuration / structure such that the air permeability of the entire separator satisfies the above-described preferable value. .

  Further, in the case of the separator having the configuration described so far, the heat shrinkage rate when left in an environment of 150 ° C. for 30 minutes can be reduced to 10% or less.

  Further, the porosity of the separator is preferably 15% or more, and preferably 20% or more in a dried state in order to secure the amount of electrolyte solution retained and to improve ion permeability. Is more preferable. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing internal short circuit, the porosity of the separator is preferably 70% or less, more preferably 60% or less, in a dry state. The porosity of the separator: P (%) can be calculated by obtaining the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following equation (1).

P = {1- (m / t) / (Σa _i · ρ _i )} × 100 (1)

Here, in the formula (1), a _i : ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (G / cm ² ), t: thickness of separator (cm).

  Furthermore, the maximum pore diameter of the separator measured by the bubble point method specified in JIS K 3832 is preferably 0.01 μm or more from the viewpoint of improving ion permeability, and internal short-circuiting due to lithium dendrite. It is preferable that it is 1 micrometer or less from a viewpoint of suppressing generation | occurrence | production more favorably.

  For the separator, for example, a composition for forming a separator prepared by dispersing inorganic particles, cellulose fibers, and a binder resin in a medium such as water (however, the binder resin may be dissolved in the medium) and polyethylene terephthalate It can be manufactured by coating on a substrate such as a (PET) plate, drying and then peeling. Moreover, in the case of the separator of a multilayer structure, you may manufacture by apply | coating the said composition for separator layer formation on the porous membrane made from polyolefin, and drying, for example.

  The separator of the present invention is used as a separator for an electrochemical element using a non-aqueous electrolyte, such as a non-aqueous electrolyte battery (a non-aqueous electrolyte primary battery and a non-aqueous electrolyte secondary battery) or a super capacitor.

  And the non-aqueous electrolyte battery of this invention is equipped with the positive electrode, the negative electrode, the non-aqueous electrolyte, and the separator of this invention.

  As the positive electrode related to the nonaqueous electrolyte, for example, a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder formed on one side or both sides of a current collector can be used.

The positive electrode active material is not particularly limited, but it is preferable to use a lithium-containing composite oxide containing at least Mn. Cellulose fibers contained in the separator are particularly excellent in the function of trapping Mn ions. Therefore, when lithium composite oxide containing Mn is used as the positive electrode active material, the effect of suppressing deterioration in properties during high-temperature storage is better. To be played. Further, since lithium-containing composite oxide containing Mn is superior in stability at a high potential, for example, to LiCoO ₂ that is widely used as a positive electrode active material for nonaqueous electrolyte batteries, this is used as a positive electrode active material. By using the battery, it is possible to increase the capacity of the battery by further increasing the end potential during charging.

  Specific examples of the lithium-containing composite oxide containing at least Mn include, for example, a spinel type lithium manganese composite oxide represented by the following general formula (2) and a layered compound represented by the following general formula (3). These may be used alone or in combination of two or more.

LiM ¹ _x Mn _2-x O ₄ (2)

In the general formula (2), M ¹ is Li, B, Mg, Ca, Sr, Ba, Ti, V, Cr, Fe, Co, Ni, Cu, Al, Sn, Sb, In, Nb, Mo, At least one element selected from the group consisting of W, Y, Ru, and Rh, and 0.01 ≦ x ≦ 0.5.

Li _a Mn _(1-b-c) Ni _b M ² _c O _{2-d Fe} (3)

In the general formula (3), M ² is selected from the group consisting of Co, Mg, Al, B, Ti, V, Cr, Fe, Cu, Zn, Zr, Mo, Sn, Ca, Sr and W. At least one element, 0.8 ≦ a ≦ 1.2, 0 <b <0.5, 0 ≦ c ≦ 0.5, d + e <1, −0.1 ≦ d ≦ 0.2, 0 <= E <= 0.1.

Further, the positive electrode active material includes LiCo _1-f M ³ _f O ₂ (M ³ is Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Lithium cobalt composite oxide represented by at least one element selected from Ba and represented by 0 ≦ f ≦ 0.5), LiNi _1-g M ⁴ _g O ₂ (M ⁴ is Al, Mg, Ti, Zr, Fe, Co, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb, and at least one element selected from Ba, and lithium nickel composite oxidation represented by 0 ≦ g ≦ 0.5) LiM ⁵ _1-h N _h PO ₄ (M ⁵ is at least one element selected from Fe, Mn and Co, where N is Al, Mg, Ti, Zr, Fe, Ni, Cu, Zn, Ga, Ge, Nb, Mo, Sn, Sb and Ba Olivine-type complex oxide represented by 0 ≦ h ≦ 0.5) may be used singly or in combination of two or more, and the spinel It can also be used in combination with the type lithium manganese composite oxide or the layered compound.

  However, in the case where a lithium-containing composite oxide containing at least Mn is used, in the positive electrode, from the viewpoint of better ensuring the effect of the use of the composite oxide, at least Mn is included in the total amount of the positive electrode active material. The proportion of the lithium-containing composite oxide (preferably the spinel type lithium manganese composite oxide and / or the layered compound) is preferably 20% by mass or more, more preferably 30% by mass or more, and 100% by mass. % May be used.

  As the positive electrode binder, for example, a fluororesin such as polyvinylidene fluoride (PVDF) is used. Moreover, as a conductive support agent of a positive electrode, carbon materials, such as carbon black, etc. are used, for example.

  The positive electrode mixture layer is prepared by, for example, preparing a positive electrode mixture-containing composition by dissolving or dispersing the positive electrode active material, the conductive additive and the binder in a solvent such as N-methyl-2-pyrrolidone (NMP). Can be applied to one or both sides of the positive electrode current collector, dried, and subjected to a press treatment as necessary. In addition, you may form the positive mix layer concerning a positive electrode by methods other than the said method.

  Further, as the positive electrode current collector, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used, but usually an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  The lead portion on the positive electrode side is normally provided by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead portion at the time of producing the positive electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.

  As the composition of the positive electrode mixture layer in the positive electrode, for example, the amount of the positive electrode active material is preferably 80 to 99% by mass, the amount of the binder is preferably 0.5 to 10% by mass, and the conductive auxiliary agent. Is preferably 0.5 to 10% by mass. Moreover, it is preferable that the thickness of a positive mix layer is 20-100 micrometers per single side | surface of a collector.

If the negative electrode which concerns on a nonaqueous electrolyte battery is a negative electrode used for nonaqueous electrolyte batteries, such as a conventionally known lithium secondary battery, ie, the negative electrode containing the active material which can occlude-release Li ion There is no particular limitation. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, simple compounds containing elements such as Si, Sn, Ge, Bi, Sb, and In, compounds and alloys thereof, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metal Alternatively, a lithium / aluminum alloy, or a Ti oxide represented by Li ₄ Ti ₅ O ₁₂ can also be used as the negative electrode active material. A negative electrode mixture in which a conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these negative electrode active materials, and a molded body (negative electrode) on one or both sides of the current collector as a core material A mixture layer) or the above-described various alloys or lithium metal foils alone or laminated as a negative electrode layer on a current collector is used.

  In the case of a negative electrode having a negative electrode mixture layer, for example, a negative electrode mixture-containing composition is prepared by dissolving or dispersing the negative electrode active material or binder in a solvent such as NMP or water. It can be formed by coating on one or both sides of the current collector and drying, and if necessary, press treatment. However, you may form the negative mix layer concerning a negative electrode by methods other than the said method.

  When the negative electrode mixture layer is formed on one side or both sides of the current collector, the thickness of the negative electrode mixture layer is preferably 20 to 200 μm per one side of the current collector.

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm. Further, the lead portion on the negative electrode side may be formed in the same manner as the lead portion on the positive electrode side.

  In the negative electrode mixture layer related to the negative electrode, the content of the negative electrode active material is preferably 88 to 99% by mass, and the content of the binder is preferably 1 to 12% by mass. When a conductive additive is used, The content is preferably 0.5 to 6% by mass.

  In the nonaqueous electrolyte battery, the positive electrode and the negative electrode include a laminated body (laminated electrode body) laminated via the separator of the present invention, and a wound body (wound electrode body) wound with the laminated body. ).

For the non-aqueous electrolyte related to the non-aqueous electrolyte battery, for example, a solution (non-aqueous electrolyte) in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO _{2 ) 2, LiC (CF 3 SO} 2) 3, LiC n F 2n + 1 SO 3 (n ≧ 2), LiN (R f OSO 2) 2 [ where _{R f} is a fluoroalkyl group] organolithium salts such as; etc. Can be used.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as ethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfites such as ethylene glycol sulfite; and the like, and these may be used alone. , It may be used in combination of two or more thereof. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  In addition, for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of these nonaqueous electrolytes, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, Additives such as t-butylbenzene can be added as appropriate.

  The concentration of the lithium salt in the nonaqueous electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  Further, a known gelling agent such as a polymer may be added to the non-aqueous electrolyte (non-aqueous electrolyte solution) to form a gel (gel electrolyte).

  Examples of the form of the nonaqueous electrolyte battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  Since the non-aqueous electrolyte battery of the present invention can suppress deterioration in characteristics during high-temperature storage, the same use as that to which a conventional non-aqueous electrolyte battery is applied, including applications that may be used at high temperatures. Can be used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Production of negative electrode>
A negative electrode mixture-containing paste was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste is intermittently applied to both sides of a 10 μm-thick current collector made of copper foil, dried, and then calendered to reduce the total thickness of the negative electrode mixture layer to 142 μm. The negative electrode mixture layer was formed into a portion having a width of 110 mm and a length of 205 mm, and further cut into a shape having an exposed portion of the negative electrode current collector. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion, and a negative electrode was produced.

<Preparation of positive electrode>
The positive active material LiMn _1.5 Ni _0.5 O ₄ : 85 parts by mass, the conductive auxiliary agent acetylene black: 10 parts by mass, and the binder PVDF: 5 parts by mass using NMP as a solvent. Thus, a positive electrode mixture-containing paste was prepared. This paste is intermittently applied to both surfaces of a 15 μm thick aluminum foil to be a current collector, dried, and then subjected to a calendar treatment to adjust the thickness of the positive electrode mixture layer so that the total thickness becomes 150 μm, A portion where the positive electrode mixture layer was formed had a width of 105 mm and a length of 200 mm, and was further cut into a shape having an exposed portion of the positive electrode current collector. Furthermore, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion, and a positive electrode was produced.

<Preparation of separator>
Plate-like boehmite (average particle diameter 1 μm, aspect ratio 10) as inorganic particles: 1000 g is dispersed in 1000 g of water, and further 2% by mass of cellulose fibers having an average fiber diameter of 0.02 μm and an average fiber length of 2 μm. A composition for forming a separator was prepared by adding an aqueous dispersion containing 1300 g and a latex of SBR as a binder resin (solid content ratio 45 mass%): 23.5 g and uniformly dispersing the mixture.

  The separator layer forming composition was applied onto a PET substrate (thickness: 20 μm) using a blade coater so that the thickness after drying was 20 μm, and after drying, was peeled from the substrate to obtain a separator. .

The volume content of the plate-like boehmite in the separator calculated by setting the specific gravity of cellulose to 1.0 g / cm ³ , the specific gravity of the binder to 0.95 g / cm ³ , and the specific gravity of boehmite to 3 g / cm ³ is 90%. The volume content of SBR was 3%. Moreover, the air permeability of the obtained separator was 150 sec / 100 ml.

<Battery assembly>
The 11 negative electrodes and 10 positive electrodes were laminated via the separator to obtain a laminated electrode body. In addition, it laminated | stacked so that both ends of a laminated electrode body might become a negative electrode. Next, each positive electrode tab was ultrasonically welded to an aluminum positive electrode external terminal, and each negative electrode tab was ultrasonically welded to a copper negative electrode external terminal.

Two metal laminate films (rectangular, size 130 mm × 240 mm) having a three-layer structure of 150 μm in thickness comprising a polyester film / aluminum film / modified polyolefin film are used as an exterior body, the laminated electrode body, and a non-aqueous electrolyte solution. A solution obtained by dissolving LiPF ₆ at a concentration of 1.2 mol / l in a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2 is sealed in the exterior body, so that the appearance shown in FIG. A nonaqueous electrolyte battery (lithium secondary battery) having the structure shown in FIG. 2 was obtained.

  Here, FIG. 1 and FIG. 2 will be described. FIG. 2 is a plan view schematically showing a nonaqueous electrolyte battery, and FIG. 2 is a cross-sectional view taken along the line II of FIG. The nonaqueous electrolyte battery 1 includes a laminated electrode body 5 constituted by laminating 10 positive electrodes and 11 negative electrodes through a separator in a laminated film outer package 2 constituted by two metal laminated films, An electrolyte (not shown) is accommodated, and the laminate film outer package 2 is sealed by thermally fusing the upper and lower laminate films at the outer peripheral portion thereof. In FIG. 2, in order to avoid complication of the drawing, each layer constituting the laminate film outer package 2 and each positive electrode, each negative electrode and each separator constituting the laminated electrode body 5 are distinguished. Not shown.

  Each positive electrode constituting the laminated electrode body 5 is connected to the positive electrode external terminal 3 by a tab in the battery 1, and each negative electrode constituting the laminated electrode body 5 is also not shown in the battery 1. The tab is connected to the negative external terminal 4. The positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out to the outside of the laminate film exterior body 2 so that they can be connected to an external device or the like.

(Example 2)
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was changed to Li ₄ Ti ₅ O ₁₂ .

  Further, a separator-forming composition was prepared in the same manner as in Example 1 except that the amount of the aqueous dispersion containing cellulose fibers was 6400 g and the amount of the SBR latex was 30 g, and this separator-forming composition was used. A separator was produced in the same manner as in Example 1 except that. The volume content of plate boehmite in the separator obtained in the same manner as in Example 1 was 70%, and the volume content of SBR was 3%. Moreover, the air permeability of the obtained separator was 850 sec / 100 ml.

  And the nonaqueous electrolyte battery was produced like Example 1 except having used the said negative electrode and the said separator.

(Example 3)
A separator forming composition was prepared in the same manner as in Example 1 except that the amount of the aqueous dispersion containing cellulose fibers was 2100 g and the amount of the SBR latex was 88 g, except that this separator forming composition was used. Produced a separator in the same manner as in Example 1. The volume content of the plate boehmite in the separator obtained in the same manner as in Example 1 was 80%, and the volume content of SBR was 10%. Moreover, the air permeability of the obtained separator was 770 sec / 100 ml.

  And the nonaqueous electrolyte battery was produced like Example 2 except having used the said separator.

(Example 4)
A separator-forming composition was prepared in the same manner as in Example 1 except that the amount of the aqueous dispersion containing cellulose fibers was 3950 g and the amount of the SBR latex was 9 g, except that this separator-forming composition was used. Produced a separator in the same manner as in Example 1. The volume content of the plate boehmite in the separator obtained in the same manner as in Example 1 was 80%, and the volume content of SBR was 10%. Moreover, the air permeability of the obtained separator was 230 sec / 100 ml.

  And the nonaqueous electrolyte battery was produced like Example 1 except having used the above-mentioned separator.

(Example 5)
Kaolin (average particle diameter 0.8 μm, aspect ratio 15): inorganic particles: 1000 g of water dispersed in 1500 g of water, and further the same aqueous dispersion of cellulose fibers as used in Example 1, 3250 g, and binder resin SBR latex (solid content ratio 45% by mass): 24.5 g was added and dispersed uniformly to prepare a separator-forming composition. And the separator was produced like Example 1 except having used this composition for separator formation.

The volume content of kaolin in the separator calculated with the specific gravity of cellulose being 1.0 g / cm ³ , the specific gravity of the binder being 0.95 g / cm ³ , and the specific gravity of kaolin being 2.6 g / cm ³ is 80%, and SBR The volume content of was 3%. Moreover, the air permeability of the obtained separator was 30 sec / 100 ml.

  And the nonaqueous electrolyte battery was produced like Example 1 except having used the above-mentioned separator.

(Comparative Example 1)
Plate-like boehmite which is inorganic particles (average particle diameter 1 μm, aspect ratio 10): 500 g is dispersed in 500 g of water, and further, an aqueous dispersion of cellulose fibers same as that used in Example 1 is 5150 g, and a binder resin. SBR latex (solid content ratio 45% by mass): 17.5 g was added and dispersed uniformly to prepare a separator-forming composition. And the separator was produced like Example 1 except having used this composition for separator formation. The volume content of the plate boehmite in the separator obtained in the same manner as in Example 1 was 60%, and the volume content of SBR was 3%. Moreover, the air permeability of the obtained separator was 2200 sec / 100 ml.

  And the nonaqueous electrolyte battery was produced like Example 1 except having used the above-mentioned separator.

(Comparative Example 2)
A separator-forming composition was prepared in the same manner as in Example 1 except that the amount of the aqueous dispersion containing cellulose fibers was 700 g and the amount of the SBR latex was 23 g, except that this separator-forming composition was used. Produced a separator in the same manner as in Example 1. The volume content of plate boehmite in the separator obtained in the same manner as in Example 1 was 93%, and the volume content of SBR was 3%. Moreover, the air permeability of the obtained separator was 770 sec / 100 ml.

  However, since the obtained separator had very low air permeability and the air permeability could not be measured, a non-aqueous electrolyte battery using this was not manufactured.

(Comparative Example 3)
A separator forming composition was prepared in the same manner as in Example 1 except that the amount of the aqueous dispersion containing cellulose fibers was 1450 g and the amount of the SBR latex was 115 g, except that this separator forming composition was used. Produced a separator in the same manner as in Example 1. The volume content of plate boehmite in the separator obtained in the same manner as in Example 1 was 80%, and the volume content of SBR was 13%. Moreover, the air permeability of the obtained separator was 5000 sec / 100 ml.

  And the nonaqueous electrolyte battery was produced like Example 1 except having used the above-mentioned separator.

  The following evaluation was performed about each nonaqueous electrolyte battery of Examples 1-5 and Comparative Examples 1 and 3.

  First, the nonaqueous electrolyte batteries of Examples 1 to 5 and Comparative Examples 1 and 3 were initialized under the following conditions, and then a charge / discharge test was performed.

  Initialization of the battery was performed at a current value of 0.2 C, with each battery of Example 1, Comparative Example 1 and Comparative Example 3 up to a charging voltage of 5.0 V, and up to 4.2 V for the other batteries. After performing constant current charging under the conditions, the former battery is 5.0 V, the latter battery is 4.2 V, and constant voltage charging is performed in a total charging time of 15 hours. This was carried out by leaving the substrate in a room temperature environment for a day and then discharging to 3.0 V at a current value of 0.2C.

  Next, the battery was charged under the following conditions to determine the charge capacity and the discharge capacity, and the ratio of the discharge capacity to the charge capacity was evaluated as the charge efficiency. Charging is performed at a current value of 0.2 C until the battery voltage reaches 5.0 V for each battery of Example 1, Comparative Example 1 and Comparative Example 3, and 4.2 V for the other batteries. Then, constant current charging was performed, and then constant current-constant voltage charging was performed at 5.0 V for the former battery and 4.2 V for the latter battery. The total charging time until the end of charging was 15 hours. Each battery after charging was discharged at a discharge current of 0.2 C until the battery voltage reached 3.0V. The batteries of Examples 1 to 5 and the batteries of Comparative Examples 1 and 3 had a charge / discharge efficiency of almost 100%, and were confirmed to operate normally as batteries.

  Next, charge / discharge cycle characteristics were evaluated for the batteries of Examples 1 to 5 and the batteries of Comparative Examples 1 and 3 by repeating charge and discharge under the following conditions.

  Charging is performed at a constant current until the battery voltage reaches 5.0 V for each battery of Example 1, Comparative Example 1 and Comparative Example 3, and 4.2 V for the other batteries. Then, charging was performed, and then constant current-constant voltage charging was performed at 5.0 V for the former battery and 4.2 V for the latter battery at constant voltage charging. The total charging time until the end of charging was 3 hours. Each battery after charging was discharged at a discharge current of 1 C until the battery voltage reached 3.0V. For each battery, this test was repeated 100 times, and the ratio of the discharge capacity at the 100th time to the discharge capacity at the first time was determined and used as the capacity retention rate after the charge / discharge cycle.

Moreover, the thermal contraction rate measurement was performed about the same separator as what was used for the battery of Examples 1-5 and Comparative Examples 1 and 3. FIG. Cut each separator to a size of 10 cm x 5 cm to prepare a test piece. Parallel to the longitudinal direction and the width direction of these test pieces, each 3 cm line is at the intersection of both lines at the center of each line. I drew it with an oil-based pen. Then, each test piece was preserve | saved for 1 hour in a 150 degreeC thermostat. Each test piece after storage is taken out from the thermostat, and the length X (cm) of the longitudinal line and the transverse line is measured, and the thermal contraction rate in the longitudinal direction and the transverse direction of the separator based on the following formula ( %) And the larger value was taken as the thermal shrinkage of the separator.
Thermal contraction rate (%) = 100 × (3-X) / 3

  The structure of the porous layer in the separators according to the batteries of the examples and comparative examples is shown in Table 1, and the physical properties of the separators and the evaluation results are shown in Table 2. The “ratio of inorganic particles in the total of inorganic particles and cellulose fibers” in Table 1 means the content ratio of inorganic particles when the total of inorganic particles and cellulose fibers is 100% by volume.

  As shown in Table 1 and Table 2, the nonaqueous electrolyte batteries of Examples 1 to 5 using the separator made of a porous layer in which the content ratio of the inorganic particles and the cellulose fiber and the content ratio of the binder resin are appropriate, Although the capacity retention rate after 100 cycles was 90% or more and good charge / discharge cycle characteristics were shown, the batteries of Comparative Examples 1 and 3 had capacity retention rates after 100 cycles of 45% and 30%, respectively. The charge / discharge cycle characteristics were inferior to those of the batteries.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte battery 2 Laminate film exterior body 3 Positive electrode external terminal 4 Negative electrode external terminal 5 Laminated electrode body

Claims (8)

A separator for an electrochemical element having at least a porous layer containing inorganic particles, cellulose fibers, and a binder resin,
When the total of the inorganic particles and the cellulose fibers is 100% by volume, the content ratio of the inorganic particles is 70 to 95% by volume,
The separator for an electrochemical element, wherein a content ratio of the binder resin in the porous layer is 0.1 to 4% by mass.   The separator for an electrochemical element according to claim 1, wherein an average fiber diameter of the cellulose fibers is 0.05 μm or less.   The separator for an electrochemical element according to claim 1 or 2, wherein the inorganic particles have an average particle diameter of 0.01 to 3.0 µm.   The separator for an electrochemical element according to any one of claims 1 to 3, which has an air permeability of 50 to 1000 sec / 100 ml.   The separator for an electrochemical element according to any one of claims 1 to 4, wherein the inorganic particles are at least one kind of particles selected from the group consisting of alumina, silica, kaolin, barium sulfate, and boehmite.   The separator for an electrochemical device according to any one of claims 1 to 5, wherein a thermal shrinkage rate when left to stand in a temperature atmosphere of 150 ° C for 30 minutes is 10% or less.   A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator for an electrochemical element according to claim 1 is used as the separator.   The nonaqueous electrolyte battery according to claim 7, wherein the positive electrode contains a lithium-containing composite oxide containing at least Mn as a positive electrode active material.

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