JP2011100602A - Nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery that is highly reliable and provides high output power. <P>SOLUTION: The nonaqueous electrolyte battery includes a multilayer porous film as a separator, the multilayer porous film having a heat-resistant porous layer which contains heat-resistant particles as a main component, is 3 to 6 μm in thickness, and has a porosity of 55% or higher, and a resin porous film which contains a thermoplastic resin as a main component. The nonaqueous electrolyte battery has a power output density of 1,200 W/kg or higher when its remaining capacity is 50% of its full charge capacity. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-power non-aqueous electrolyte battery excellent in reliability.

  Lithium secondary batteries, which are a type of non-aqueous electrolyte battery, are widely used as power sources for portable devices such as mobile phones and notebook personal computers because of their high energy density. It is also spreading to high output applications such as Furthermore, in the future, from the viewpoint of environmental problems and energy problems, rapid development of in-vehicle high-power lithium secondary batteries aimed at application to electric vehicles, plug-in hybrid electric vehicles, and hybrid electric vehicles is required.

  In current lithium secondary batteries, a polyolefin-based porous film having a thickness of, for example, about 15 to 30 μm is used as a separator interposed between a positive electrode and a 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 having a low melting point may be applied.

  By the way, as such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used for increasing the porosity and improving the strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is secured by the stretching. However, with such a stretched film, the degree of crystallinity has increased, and the shutdown temperature has increased to a temperature close to the thermal runaway temperature of the battery. Therefore, it can be said that the margin for ensuring the safety of the battery is sufficient. hard.

  In addition, the film is distorted by the stretching, and there is a problem that when it is exposed to a high temperature, shrinkage occurs due to residual stress. The shrinkage temperature is very close to the shutdown temperature. For this reason, when a polyolefin-based porous film separator is used, when the battery temperature reaches the shutdown temperature in the case of abnormal charging, the current must be immediately decreased to prevent the battery temperature from rising. This is because if the pores are not sufficiently closed and the current cannot be reduced immediately, the battery temperature easily rises to the contraction temperature of the separator, and there is a risk of ignition due to an internal short circuit.

  As a technique for preventing such a short circuit due to thermal contraction of the separator and improving the reliability of the battery, for example, a multilayer in which a layer having high heat resistance is formed on the surface of a resin porous film (microporous film) serving as a base Structured separators have been proposed (for example, Patent Documents 1 to 5). By using these separators, for example, thermal runaway hardly occurs even when abnormal overheating occurs, and a battery having excellent reliability can be configured.

JP 2006-351386 A JP 2007-273123 A JP 2007-273443 A JP 2007-280911 A International Publication No. 2009/44741

  By the way, in the case of the high output type lithium secondary battery as described above, higher reliability is required than the conventional lithium secondary battery. For example, when the reliability of a lithium secondary battery is increased by using the separator having the multilayer structure described above, the presence of a high heat resistance layer related to the separator is important for improving the reliability of the battery. The higher layer generally also acts as a layer that inhibits the movement of lithium ions passing through the separator. Therefore, in a lithium secondary battery configured using a separator having a multilayer structure, the presence of the high heat-resistant layer may cause, for example, a reduction in output characteristics.

  For this reason, in the case of using the multi-layered separator from the viewpoint of improving reliability in a high-power lithium secondary battery, the reduction in output characteristics due to the high heat-resistant layer is also considered. It is required to do.

  This invention is made | formed in view of the said situation, The objective is to provide the high output non-aqueous electrolyte battery excellent in reliability.

  The non-aqueous electrolyte battery of the present invention that has achieved the above object comprises a heat-resistant porous layer containing heat-resistant fine particles as a main component, having a thickness of 3 to 6 μm and a porosity of 55% or more, and a thermoplastic resin. A multilayer porous membrane having a resin porous membrane as a main component is provided as a separator, and the output density when the remaining capacity with respect to the full charge capacity is 50% (hereinafter sometimes simply referred to as “output density”). Is) 1200 W / kg or more.

  As used herein, the “full charge capacity” of a non-aqueous electrolyte battery means that the battery is charged with a constant current at a current value of 0.5 C up to 4.2 V, and further charged with a constant voltage at 4.2 V. It means the capacity when charging is stopped when the value drops to 0.025C (that is, fully charged) and discharged from this state to 3.0V at a current value of 0.2C. .

  ADVANTAGE OF THE INVENTION According to this invention, the high output nonaqueous electrolyte battery excellent in reliability can be provided.

  The non-aqueous electrolyte battery of the present invention includes a heat-resistant porous layer containing heat-resistant fine particles as a main component, having a thickness of 3 to 6 μm and a porosity of 55% or more, and a resin porous mainly containing a thermoplastic resin. A multi-layer porous membrane having a membrane is used as a separator, thereby suppressing a decrease in output density due to introduction of a heat-resistant porous layer while improving reliability, and a high-power battery having an output density of 1200 W / kg or more It is said.

  For example, in a high-power battery with an output density exceeding 1000 W / kg, the output is generated when a foreign matter such as a metal piece, a thermal contraction of the separator due to the battery being exposed to high temperature, or an internal short circuit due to a film breakage, etc. Compared to batteries with low density, there is a higher risk that a large current will be concentrated instantaneously at the short-circuited location, leading to thermal runaway.

  In the battery of the present invention, even when the output density of the battery is 1200 W / kg or more, the heat-resistant porous layer containing the heat-resistant fine particles of the separator melts or breaks down when a large current flows through the short-circuited part during a short circuit. Therefore, the short-circuit phenomenon can be made extremely localized, and even during abnormal heat generation, the heat shrinkage rate of the separator is greatly reduced due to the presence of the heat-resistant porous layer, and thus it occurs between the positive and negative electrodes. Short circuit can be suppressed.

  Further, the heat resistant porous layer according to the separator has an action of inhibiting the movement of lithium ions in the separator, but in the battery of the present invention, by appropriately adjusting the structure of the heat resistant porous layer as described above, The influence on the movement of lithium ions is suppressed as much as possible, and a power density of 1200 W / kg or more can be secured.

  In the multilayer porous membrane used in the separator according to the battery of the present invention, the resin porous membrane is a layer having the original function of a separator that transmits ions while preventing a short circuit between the positive electrode and the negative electrode. The layer is a layer that plays a role of imparting heat resistance to the separator.

  In the heat-resistant porous layer, the heat-resistant fine particles are the main components, and play a role of preventing thermal shrinkage and film breakage of the resin porous film serving as the base material. In addition, when the inside of the battery generates heat abnormally and the resin porous membrane melts, the positive and negative electrodes are separated by the heat-resistant porous layer containing heat-resistant fine particles as the main component, ensuring the reliability of the battery. The

  The heat-resistant fine particles have electrical insulation properties, are electrochemically stable, and are stable in a solvent used for an organic electrolyte and a composition for forming a heat-resistant porous layer (a composition containing a solvent) described later. As long as it does not dissolve in the organic electrolyte at high temperature, there is no particular limitation. As used herein, “stable heat-resistant fine particles with respect to an organic electrolyte” refers to deformation and chemical composition in an organic electrolyte (an organic electrolyte used as an electrolyte in a non-aqueous electrolyte battery). It means heat-resistant fine particles that do not change. In addition, the “high temperature state” in the present specification specifically refers to a temperature of 150 ° C. or higher, and may be a stable particle that does not undergo deformation or chemical composition change in an organic electrolyte at such a temperature. That's fine. Further, “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the battery.

Specific examples of such heat-resistant fine particles include, for example, oxide fine particles such as iron oxide, SiO ₂ (silica), Al ₂ O ₃ (alumina), TiO ₂ , BaTiO ₃ , ZrO ₂ ; aluminum nitride, silicon nitride Nitride fine particles such as: Calcium fluoride, barium fluoride, barium sulfate and other poorly soluble ionic crystal fine particles; silicon, diamond and other covalently bonded crystal fine particles; talc, montmorillonite and other clay fine particles; boehmite, zeolite, apatite, Inorganic fine particles such as kaolin, mullite, spinel, olivine, sericite, bentonite and other mineral resource-derived substances or artificial products thereof. Further, the surface of conductive fine particles such as metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbon fine particles such as carbon black and graphite; It may be fine particles that have been made electrically insulating by surface treatment with the above-mentioned materials constituting the electrically insulating heat-resistant fine particles. Furthermore, polymer fine particles such as crosslinked polymethyl methacrylate (crosslinked PMMA) can also be used. These heat resistant fine particles may be used alone or in combination of two or more. As the heat-resistant fine particles, silica, alumina and boehmite are more preferable, alumina and boehmite are more preferable, and boehmite is particularly preferable.

  Examples of the shape of the heat-resistant fine particles include various shapes such as a spherical shape, a particle shape, a plate shape, and a needle shape. From the viewpoint of better suppressing the thermal shrinkage of the separator, the aspect ratio is 1 or more and 3 or less. It is preferably a polyhedral shape or a substantially spherical shape (including a true spherical shape). The term “polyhedron-shaped particle” as used herein refers to a particle surrounded by a substantially polygonal surface (including a polygon), and has a substantially rhombohedral shape (including rhombohedral shape), a substantially hexagonal column shape (hexagonal column). And particles having a substantially cubic shape (including a cubic shape).

  The aspect ratio of a polyhedral particle is the distance Lf (μm) from the center (center of gravity) of the particle to the center of the farthest surface, and the distance Ln (μm) from the center of the particle to the nearest surface center. It means the value obtained by dividing, ie, “Lf / Ln”. The aspect ratio of the substantially spherical particles is a value obtained by dividing the major axis diameter (longest diameter) Ll (μm) of the sphere by the minor axis diameter (shortest diameter) Ls (μm) of the sphere, that is, It means “Ll / Ls”. From these definitions, the aspect ratio of the heat-resistant fine particles is 1 or more.

  In the case of heat-resistant fine particles having an aspect ratio exceeding 3, when the heat-resistant porous layer is formed in a resin porous film shape, the lithium is in a direction parallel to the resin porous film, that is, during charge / discharge. Since particles tend to be oriented in a direction perpendicular to the direction of ion movement, there is a risk of a barrier against the movement of lithium ions moving between the positive and negative electrodes. There is a possibility that the porosity of the heat resistant porous layer may be lowered. Therefore, when heat-resistant fine particles having an aspect ratio exceeding 3 are used, the effect of improving the output density of the battery may be reduced.

  As used herein, the aspect ratio of the heat-resistant fine particles is obtained by image analysis of the surface and cross section of the heat-resistant porous layer, for example, an image taken at a measurement magnification of about 3000 to 20000 times with a scanning electron microscope (SEM). Thus, the above-mentioned Ln and Lf, or Ll and Ls can be obtained and calculated from them (the aspect ratio of the heat-resistant fine particles shown in the examples described later is a value obtained by this method).

  If the heat-resistant fine particles are too large, it is difficult to form a thin heat-resistant porous layer, and the movement of lithium ions tends to be an obstacle, so the average particle diameter is preferably 1 μm or less. More preferably, it is 8 μm or less. On the other hand, if the heat-resistant fine particles are too small, the surface area becomes large, so that the dispersibility of the heat-resistant fine particles in the heat-resistant porous layer is reduced or the amount of water adhering to the heat-resistant fine particles is increased. It becomes difficult to control the amount. If the amount of water in the battery increases, the battery characteristics may deteriorate. Therefore, the average particle diameter of the heat-resistant fine particles is preferably 0.2 μm or more from the viewpoint of suppressing the occurrence of such problems and making it possible to construct a battery having good characteristics.

  In addition, the average particle diameter of the heat-resistant fine particles referred to in this specification is a medium that does not swell or dissolve the fine particles using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA) (for example, water). The particle size (D50) at 50% of the volume-based integrated fraction measured by dispersing in a particle size.

  The heat-resistant porous layer contains heat-resistant fine particles as a main component. The term “containing as a main component” as used herein means that the heat-resistant fine particles contain 70% by volume or more in the total volume of components of the heat-resistant porous layer. Means. The amount of the heat-resistant fine particles in the heat-resistant porous layer is preferably 80% by volume or more and more preferably 90% by volume or more in the total volume of the constituent components of the heat-resistant porous layer. By making the heat-resistant fine particles in the heat-resistant porous layer have a high content as described above, the heat shrinkage of the entire multilayer porous film can be satisfactorily suppressed. The heat-resistant porous layer preferably contains a binder for binding the heat-resistant fine particles to each other or binding the heat-resistant porous layer and the resin porous film. The suitable upper limit of the amount of heat-resistant fine particles in the heat-resistant porous layer is, for example, 99% by volume in the total volume of the constituent components of the heat-resistant porous layer. If the amount of the heat-resistant fine particles in the heat-resistant porous layer is less than 70% by volume, for example, it is necessary to increase the amount of the binder in the heat-resistant porous layer. There is a risk of losing the function as a separator, for example, when it is filled with a binder, and when it is made porous using a pore-opening agent or the like, the interval between the heat-resistant fine particles becomes too large, causing heat shrinkage. There is a possibility that the effect of suppressing the decrease.

  The heat-resistant porous layer preferably contains a binder for the purpose of binding the heat-resistant fine particles to each other or bonding the heat-resistant porous layer and the resin porous film. The binder is not particularly limited as long as the constituent components of the heat-resistant porous layer can be satisfactorily bonded to each other, are electrochemically stable, and are stable to the organic electrolyte. Specifically, for example, ethylene-vinyl acetate copolymer (EVA, structural unit derived from vinyl acetate is 20 to 35 mol%), acrylate copolymer, fluorine rubber, styrene butadiene rubber (SBR), polyvinyl Resins such as alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane, and polyvinylidene fluoride (PVDF) are listed. Some of these resins prevent dissolution in organic electrolytes. In order to achieve this, those having a crosslinked structure introduced can also be used. These binders may be used alone or in combination of two or more. Among these, an acrylate copolymer having a crosslinked structure is particularly preferable.

  In addition to the binder, amine compounds and polyacrylic acid resins may be mixed with known resins to increase flexibility, lower the glass transition temperature (Tg), or use known plasticizers (phthalate esters). Or the like) can be used, for example, to improve the elongation at break. Furthermore, the adhesiveness of the binder can be enhanced by introducing a carboxyl group. As a method for lowering the Tg of the resin, various known methods such as introduction of a crosslinked structure having a low crosslinking density and introduction of a long side chain can be employed.

  The amount of the binder in the heat-resistant porous layer is determined from the viewpoint of better ensuring the effect of improving the adhesion between the heat-resistant porous layer and the resin porous film by using the binder and the effect of improving the adhesion between the heat-resistant fine particles. The amount is preferably 1 part by mass or more and more preferably 2 parts by mass or more with respect to 100 parts by mass of the fine particles. However, in the heat-resistant porous layer, if the amount of the binder is too large, the pores of the heat-resistant porous layer are blocked, and battery characteristics represented by load characteristics may be deteriorated. Therefore, the amount of the binder in the heat resistant porous layer is preferably 20 parts by mass or less and more preferably 10 parts by mass or less with respect to 100 parts by mass of the heat resistant fine particles.

  The thickness of the heat-resistant porous layer (when the multilayer porous film constituting the separator has a plurality of heat-resistant porous layers, the total thickness. The same applies to the thickness of the heat-resistant porous layer). From the viewpoint of increasing the thickness, it is 6 μm or less, and preferably 5 μm or less. Further, from the viewpoint of satisfactorily suppressing the heat shrinkage of the resin porous membrane, the thickness of the heat resistant porous layer is 3 μm or more, and preferably 4 μm or more.

From the viewpoint of increasing the output density of the battery, the porosity of the heat resistant porous layer is 55% or more in a dry state (the same applies to the porosity of the heat resistant porous layer and the resin porous membrane), It is preferably 56% or more. Further, from the viewpoint of suppressing the reduction of the above-described effect by the heat resistant porous layer, the porosity of the heat resistant porous layer is preferably 70% or less, and more preferably 65% or less. The porosity of the heat resistant porous layer: P (%) is the sum of each component i using the following formula (1) from the thickness of the heat resistant porous layer, the mass per area, and the density of the constituent components. It can be calculated by finding it.
P = 100− (Σa _i / ρ _i ) × (m / t) (1)
Here, in the above formula, a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of heat-resistant porous layer (g / cm ² ), t: thickness (cm) of the heat-resistant porous layer.

  The resin porous membrane according to the multilayer porous membrane constituting the separator used in the battery of the present invention is a thermoplastic resin that is softened at 80 to 180 ° C. to close the pores and does not dissolve in the organic electrolyte solution of the battery It is preferable that the main component is. The thermoplastic resin softening at 80 to 180 ° C. is, for example, a thermoplastic resin having a melting temperature of 80 to 180 ° C. measured using a differential scanning calorimeter (DSC) according to JIS K 7121. Is mentioned. Specific examples of the thermoplastic resin include polyolefin and thermoplastic polyurethane. Examples of the polyolefin include polyethylene (PE) such as low density polyethylene, high density polyethylene, and ultrahigh molecular weight polyethylene; polypropylene (PP); As the thermoplastic resin, those exemplified above may be used alone or in combination of two or more.

  As the resin porous membrane, for example, an ion-permeable porous membrane having a large number of pores formed by a conventionally known solvent extraction method, dry type or wet drawing method (used widely as a battery separator) A layer composed of a microporous membrane) can be used.

  In the resin porous membrane, “having a thermoplastic resin as a main component” means that the component (thermoplastic resin) as a main component among the components constituting the resin porous membrane is 50% by volume or more. Means.

  In addition, the thermoplastic resin content in the resin porous membrane has a so-called shutdown effect that the thermoplastic resin constituting the resin porous membrane melts and closes the pores of the separator when the temperature inside the battery becomes high. In order to make it easier to obtain, for example, the following is preferable. The volume of the thermoplastic resin in all the constituent components of the multilayer porous membrane is preferably 10% by volume or more, and more preferably 20% by volume or more. Furthermore, the volume of the thermoplastic resin is preferably 50% by volume or more, more preferably 70% by volume or more, and more preferably 80% by volume or more in all the constituent components of the resin porous membrane. (The thermoplastic resin may be 100% by volume). Furthermore, the volume of the thermoplastic resin is preferably 50% or more of the pore volume of the heat resistant porous layer.

  The thickness of the resin porous membrane (when the multilayer porous membrane has a plurality of resin porous membranes, the total thickness. The same applies to the thickness of the resin porous membrane). From the viewpoint, it is preferably 8 μm or more, and more preferably 12 μm or more. Further, from the viewpoint of reducing the total thickness of the separator and further improving the capacity and output density of the battery, the thickness of the resin porous membrane is preferably 25 μm or less, and more preferably 20 μm or less.

  Further, the resin porous membrane preferably has a pore size of 3 μm or less. If the separator is made of a multilayer porous membrane using a resin porous membrane having a small pore diameter as described above, even if small pieces are detached from the positive electrode or the negative electrode in the battery, the occurrence of a short circuit due to this is satisfactorily suppressed. Can do.

Further, in the formula (1), m is the mass per unit area (g / cm ² ) of the resin porous membrane, and t is the thickness (cm) of the resin porous membrane. Can also be used to determine the porosity of the resin porous membrane: P (%). The porosity of the resin porous membrane required by this method is preferably 30% or more, more preferably 40% or more from the viewpoint of increasing the amount of nonaqueous electrolyte retained, and the physical properties of the resin porous membrane From the viewpoint of increasing the mechanical strength and ensuring better shutdown characteristics, it is preferably 80% or less, more preferably 70% or less.

  The multilayer porous film may have one resin porous film and one heat resistant porous layer. For example, the heat resistant porous layer has a heat resistant porous layer on both sides of the resin porous film. Or a plurality of porous resin membranes. However, increasing the number of layers increases the thickness of the multilayer porous membrane, and in a battery using a separator composed of this multilayer porous membrane, there is a risk of causing an increase in internal resistance and a decrease in energy density. It is not preferable to increase the number too much, and the total number of layers (resin porous film and heat-resistant porous layer) constituting the multilayer porous film is preferably 5 layers or less, and more preferably 2 layers.

  The thickness of the multilayer porous membrane is preferably 11 μm or more, and more preferably 15 μm or more, from the viewpoint of ensuring sufficient strength as a separator. However, if the multilayer porous membrane is too thick, the effect of increasing the output of the battery may be reduced. Therefore, the thickness of the multilayer porous membrane is preferably 32 μm or less, and more preferably 30 μm or less. .

  If the resin porous membrane is too thin relative to the thickness of the heat-resistant porous layer, most of the molten thermoplastic resin when exposed to a temperature equal to or higher than the melting point of the thermoplastic resin constituting the resin porous membrane. May be absorbed into the heat-resistant porous layer and it may be difficult to maintain the film structure, and therefore the thickness of the resin porous film in the multilayer porous film is 2.2 times or more the thickness of the heat-resistant porous layer. It is preferable that the ratio is 2.5 times or more. In addition, if the resin porous membrane is too thick relative to the thickness of the heat resistant porous layer, the effect of suppressing the thermal shrinkage rate of the multilayer porous membrane may be reduced. The thickness of is preferably 10 times or less, more preferably 6 times or less the thickness of the heat resistant porous layer.

  The heat shrinkage rate of the multilayer porous membrane according to the present invention is preferably 7% or less, and more preferably 5% or less, as measured by the method described in Examples below. If the thermal contraction rate of the multilayer porous membrane is too large, the possibility of a short circuit between the positive and negative electrodes increases due to the thermal contraction of the separator that occurs when the battery heats up abnormally, and the separator breaks down when an internal short circuit occurs. There is a possibility that the effect of suppressing the spread of the film is reduced. The thermal contraction rate of the multilayer porous membrane can be ensured by configuring the multilayer porous membrane as described above.

  The multilayer porous membrane according to the present invention is, for example, a composition for forming a heat-resistant porous layer in the form of a slurry or paste by dispersing heat-resistant fine particles and a binder constituting the heat-resistant porous layer in a medium such as water or an organic solvent. An article (a binder may be dissolved in a medium) is prepared, applied to the surface of the resin porous membrane, and dried.

  In addition, the application of the heat-resistant porous layer forming composition to the resin porous membrane surface is, for example, a method of applying the heat-resistant porous layer forming composition to the surface of the resin porous membrane with a known coating device, It can be carried out by a method of impregnating the resin porous membrane into the heat-resistant porous layer forming composition.

  Examples of the coating apparatus that can be used when applying the heat-resistant porous layer forming composition to the surface of the resin porous membrane include a gravure coater, a knife coater, a reverse roll coater, and a die coater.

  The medium used in the heat-resistant porous layer forming composition may be any medium that can uniformly disperse heat-resistant fine particles and the like, and can dissolve or disperse the binder uniformly. For example, an aromatic hydrocarbon such as toluene. Common organic solvents such as francs such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohol (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these media. In addition, when the binder is water-soluble or used as an emulsion, water may be used as described above. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately used. In addition, the interfacial tension can be controlled.

  The heat-resistant porous layer forming composition preferably has a solid content of, for example, 10 to 80% by mass.

  The resin porous membrane can be subjected to surface modification in order to enhance the adhesion with the heat resistant porous layer. As described above, the resin porous membrane is preferably made of polyolefin, but in this case, surface modification is often effective because surface adhesion is generally not high.

  Examples of the method for modifying the surface of the resin porous membrane include corona discharge treatment, plasma discharge treatment, and ultraviolet irradiation treatment. From the viewpoint of dealing with environmental problems, for example, it is more desirable to use water as the medium of the heat-resistant porous layer forming composition. From this, the hydrophilicity of the resin porous membrane surface can be improved by surface modification. It is very preferable to increase the value.

  The non-aqueous electrolyte battery of the present invention has a power density of 1200 W / kg or more and 2000 W / kg or more when the remaining capacity [State of charge (SOC)] with respect to the full charge capacity is 50%. preferable. In power supply applications for automobiles and automobiles, which are assumed to be the main application of the battery of the present invention, a high output density is required in a relatively wide discharge region. Therefore, the output density when the SOC is 50% is required. In the case of less than 1200 W / kg, there is no denying insufficient output.

  The nonaqueous electrolyte battery of the present invention is not particularly limited as long as the multilayer porous membrane is used as a separator, and the output density in a state where the SOC is 50% is 1200 W / kg or more. The configuration and structure adopted in the non-aqueous electrolyte battery can be applied. The non-aqueous electrolyte battery of the present invention includes a primary battery and a secondary battery. The configuration of a secondary battery (non-aqueous electrolyte secondary battery), which is a main application, will be described below. Illustrate.

  Examples of the form of the non-aqueous electrolyte secondary battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can 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.

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known non-aqueous electrolyte secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing lithium ions. For example, as an active material, a layered structure represented by a general formula of Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, Zr, Ti, Sn, etc.) A lithium-containing transition metal oxide, LiMn ₂ O ₄ and a spinel-type lithium manganese oxide in which a part of the element is substituted with another element, LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) An olivine type compound or the like can be used. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn [Li _{1 + a} Mn _x Ni _y Co _1-xy O ₂ (−0.1 <a <0.1, 0 <x <0.5 , 0 <y <0.8), etc.].

  As the conductive aid, a carbon material such as carbon black is used, and as the binder, a fluorine resin such as PVDF is used, and the positive electrode mixture layer is formed by a positive electrode mixture in which these materials and an active material are mixed. For example, it is formed on the current collector surface.

  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.

The negative electrode is not particularly limited as long as it is a negative electrode used in conventionally known non-aqueous electrolyte secondary batteries, that is, a negative electrode containing an active material capable of occluding and releasing lithium ions. 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. Further, compounds that can be charged and discharged at a low voltage close to lithium metal, such as elements such as Si, Sn, Ge, Bi, Sb, and In and alloys thereof, lithium-containing nitrides, or oxides such as Li ₄ Ti ₅ O ₁₂ Alternatively, lithium metal or a lithium / aluminum alloy 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 is finished into a molded body (negative electrode mixture layer) using the current collector as a core material. Or those obtained by laminating the above-mentioned various alloys or lithium metal foils alone or on the surface 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 addition, in order to set the output density of the battery to 1200 W / kg, the thickness of the positive electrode mixture layer related to the positive electrode and the thickness of the negative electrode mixture layer related to the negative electrode should be reduced to increase the facing area of the positive and negative electrodes. Preferably, specifically, the mass of the positive electrode mixture layer is 12 mg / cm ² or less per side of the positive electrode current collector, and the mass of the negative electrode mixture layer is 6 mg / cm ² or less per side of the negative electrode current collector. It is preferable to do. In addition, if the mass of the mixture layer per one side of the current collector becomes too low, the mass ratio occupied by the current collector, separator, and exterior material other than the mixture layer inside the battery becomes too large. On the other hand, the output density of the battery tends to decrease. Therefore, the mass of the positive electrode mixture layer is preferably 5 mg / cm ² or more per side of the positive electrode current collector, and the mass of the negative electrode mixture layer is 2 mg / cm ² or more per side of the negative electrode current collector. It is preferable.

  The electrode can be used in the form of a laminated electrode body in which the positive electrode and the negative electrode are laminated via a separator made of the multilayer porous film of the present invention, or a wound electrode body in which this is wound. .

As the organic electrolytic solution, a solution 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, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, 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 (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent used in the organic electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, 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 1,2-dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran, 2-methyltetrahydrofuran; acetonitrile, propionitrile, methoxypropio Nitriles such as nitriles; sulfites such as ethylene glycol sulfite; and the like. Rukoto can also. 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, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, t are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. -Additives such as butylbenzene can be added as appropriate.

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

  Also, instead of the organic solvent, melting at room temperature such as ethyl-methylimidazolium trifluoromethylsulfonium imide, heptyl-trimethylammonium trifluoromethylsulfonium imide, pyridinium trifluoromethylsulfonium imide, guanidinium trifluoromethylsulfonium imide A salt can also be used.

  Furthermore, PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, main chain or An electrolyte gelled using a known host polymer capable of forming a gel electrolyte such as a crosslinked polymer containing an ethylene oxide chain in the side chain or a crosslinked poly (meth) acrylate ester can also be used.

  The non-aqueous electrolyte battery of the present invention is conventionally known for use in power supplies for electric tools and automobiles, particularly for applications that require high output, and for power supplies for various electronic devices. The present invention can also be applied to the same applications as those used in which nonaqueous electrolyte batteries are used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. In addition, D10 and D90 of the heat-resistant fine particles in Example 1 described later are a particle size at 10% and a particle size at 90% in the volume-based integrated fraction measured by the same method as D50, respectively.

Example 1
<Preparation of multilayer porous membrane>
In 1000 g of water, 1000 g of a hexahedron-shaped boehmite synthetic product (aspect ratio 1.4, D10 = 0.31 μm, D50 = 0.4 μm, D90 = 0.92 μm) as heat-resistant fine particles and an acrylate co-binder A polymer (commercially available acrylate copolymer mainly composed of butyl acrylate as a monomer component; 3 parts by mass with respect to 100 parts by mass of heat-resistant fine particles) is dispersed by stirring for 1 hour using a three-one motor and uniform. Slurry (composition for forming a heat resistant porous layer) was prepared.

As the porous resin membrane, a PE microporous membrane having a thickness of 16 μm and a porosity of 40% and subjected to corona discharge treatment on one side was prepared. The slurry is uniformly applied to the surface of the PE microporous membrane on the side subjected to corona discharge treatment using a die coater so that the thickness after drying becomes 3 μm, and dried to obtain a multilayer porous membrane. Was made. The heat-resistant porous layer according to the multilayer porous membrane has a mass of 0.35 mg / cm ² , a porosity of 59%, a boehmite specific gravity of 3 g / cm ³ , and a binder specific gravity of 1 g / cm ³ . The volume ratio of the heat-resistant fine particles calculated as ³ was 91.7% by volume.

<Preparation of positive electrode plate>
LiNi _0.6 Co _0.2 Mn _0.2 O ₂ powder as a positive electrode active material: 87% by mass, PVDF as a binder: 5% by mass, and acetylene black as a conductive auxiliary agent: 8% by mass are mixed. A positive electrode mixture-containing slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) thereto. This slurry was applied to both surfaces of an aluminum foil having a thickness of 20 μm serving as a positive electrode current collector so that the total thickness after drying was 55 μm and dried to obtain a positive electrode plate. The mass of the positive electrode mixture layer in the positive electrode plate was 10.5 mg / cm ² per one side of the positive electrode current collector.

<Preparation of negative electrode plate>
Artificial graphite powder as a negative electrode active material: 90% by mass, PVDF as a binder: 5% by mass, and acetylene black as a conductive auxiliary agent: 5% by mass are mixed into a negative electrode mixture, and NMP is added thereto. A paste-like negative electrode mixture-containing slurry was prepared. This slurry was applied to both sides of a 10 μm thick copper foil serving as a negative electrode current collector so that the total thickness after drying was 46 μm and dried to obtain a negative electrode plate. The mass of the negative electrode mixture layer in the negative electrode plate was 5 mg / cm ² per one side of the negative electrode current collector.

<Battery assembly>
The positive electrode plate was slit to a width of 54 mm and the negative electrode plate to a width of 56 mm, and the multilayer porous film slit to a width of 58.5 mm was interposed as a separator between the positive electrode plate and the negative electrode plate. While being overlapped and wound in a spiral shape, a wound electrode body was obtained. This wound electrode body was inserted into a 18650 cylindrical battery can, and an organic electrolyte (LiPF ₆ was mixed with a solvent in which ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were mixed at a volume ratio of 1: 1: 2 at 1 mon / Then, the battery can was sealed to produce a cylindrical non-aqueous electrolyte secondary battery.

Example 2
A multilayer porous membrane was prepared in the same manner as in Example 1 except that the thickness of the heat-resistant porous layer was 6 μm, and a cylindrical non-aqueous solution was prepared in the same manner as in Example 1 except that this multilayer porous membrane was prepared. An electrolyte secondary battery was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.48 mg / cm ² and a porosity of 59%.

Example 3
A multilayer porous membrane was prepared in the same manner as in Example 1 except that the heat-resistant fine particles used in the heat-resistant porous layer were changed to a spherical alumina synthetic product (aspect ratio 1.0, D50 = 1.0 μm). A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this multilayer porous membrane was produced. The heat-resistant porous layer according to the multilayer porous membrane has a mass of 0.48 mg / cm ² , a porosity of 55%, an alumina specific gravity of 4 g / cm ³ , and a binder specific gravity of 1 g / cm ³ . The volume ratio of the heat-resistant fine particles calculated as ³ was 91.7% by volume.

Example 4
A multilayer porous membrane was prepared in the same manner as in Example 3 except that the thickness of the heat-resistant porous layer was changed to 6 μm. A cylindrical non-aqueous solution was prepared in the same manner as in Example 1 except that this multilayer porous membrane was prepared. An electrolyte secondary battery was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.92 mg / cm ² and a porosity of 59%.

Example 5
The heat-resistant fine particles used in the heat-resistant porous layer are changed to hexahedron-shaped boehmite synthetic products (aspect ratio 1.4, D50 = 0.2 μm), and the resin porous film has a thickness of 25 μm and a porosity of 40%, except that it was changed to a PE microporous membrane with a corona discharge treatment on one side, a multilayer porous membrane was prepared in the same manner as in Example 1, and this multilayer porous membrane was manufactured except that this multilayer porous membrane was manufactured. A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.35 mg / cm ² and a porosity of 62%.

Example 6
A multilayer porous membrane was prepared in the same manner as in Example 5 except that the thickness of the heat-resistant porous layer was changed to 6 μm, and a cylindrical non-aqueous solution was prepared in the same manner as in Example 1 except that this multilayer porous membrane was prepared. An electrolyte secondary battery was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.7 mg / cm ² and a porosity of 62%.

Example 7
A multilayer porous membrane was prepared in the same manner as in Example 5 except that the heat-resistant fine particles used for the heat-resistant porous layer were changed to hexahedron-shaped boehmite synthesized products (aspect ratio 1.4, D50 = 1.0 μm). A cylindrical non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this multilayer porous membrane was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.35 mg / cm ² and a porosity of 55%.

Example 8
A multilayer porous membrane was prepared in the same manner as in Example 7 except that the thickness of the heat-resistant porous layer was 6 μm, and a cylindrical non-aqueous solution was prepared in the same manner as in Example 1 except that this multilayer porous membrane was prepared. An electrolyte secondary battery was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.7 mg / cm ² and a porosity of 55%.

Comparative Example 1
A multilayer porous membrane was prepared in the same manner as in Example 1 except that the heat-resistant fine particles used in the heat-resistant porous layer were changed to a plate-like boehmite synthetic product (aspect ratio 10, D50 = 1.0 μm). A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this multilayer porous membrane was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.39 mg / cm ² and a porosity of 52%.

Comparative Example 2
A multilayer porous membrane was prepared in the same manner as in Example 1 except that the thickness of the heat-resistant porous layer was changed to 2.2 μm. A cylindrical shape was prepared in the same manner as in Example 1 except that this multilayer porous membrane was prepared. A non-aqueous electrolyte secondary battery was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 0.27 mg / cm ² and a porosity of 59%.

Comparative Example 3
A multilayer porous membrane was prepared in the same manner as in Example 1 except that the thickness of the heat-resistant porous layer was 8 μm, and a cylindrical non-aqueous solution was prepared in the same manner as in Example 1 except that this multilayer porous membrane was prepared. An electrolyte secondary battery was produced. The heat-resistant porous layer according to the multilayer porous membrane had a mass of 1.2 mg / cm ² and a porosity of 58%.

Comparative Example 4
Example 1 except that a PE microporous membrane having a thickness of 30 μm and a porosity of 40% and subjected to corona discharge treatment on one side was used as a separator without forming a heat resistant porous layer. A cylindrical non-aqueous electrolyte secondary battery was produced.

The thermal contraction rate of the multilayer porous membrane used as a separator in the cylindrical nonaqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4 was measured by the following method. The multilayer porous membrane was cut into a rectangle of 5 cm in length and 10 cm in width, and a cross line of 3 cm in parallel with the vertical direction and 3 cm in parallel with the horizontal direction was drawn with black ink. When the multilayer porous membrane is cut into a rectangle, the longitudinal direction or the lateral direction is the production direction of the multilayer porous membrane (for example, the resin porous membrane constituting the separator is obtained through a stretching process) And the cross line of the cross line is the center of the multilayer porous membrane piece. Thereafter, the multilayer porous membrane piece was suspended in a thermostatic bath, the bath temperature was increased to 160 ° C. at a rate of 5 ° C./min, and the temperature was further maintained at 160 ° C. for 1 hour. Then, after taking out and cooling the multilayer porous membrane piece, the shorter length d (mm) of the crosshairs was measured, and the thermal shrinkage rate (%) was calculated by the following formula.
Heat shrinkage rate = 100 × (30−d) / 30
The measurement was performed three times for each multilayer porous membrane, and the average value thereof was taken as the thermal shrinkage rate of each multilayer porous membrane.

  Moreover, about the cylindrical nonaqueous electrolyte secondary battery of Examples 1-8 and Comparative Examples 1-4, the following output density measurements, load characteristic measurements, and heating tests were performed.

<Output density measurement>
After each battery was charged to 4.2 V, discharge treatment was performed until the SOC reached 50%, and then the battery was discharged at a predetermined current for 20 seconds. The discharge current was 0.5A, 1A, 3A, 5A and 10A. And the battery voltage 10 second after the discharge start was measured at the time of each discharge. The current value at the lower limit voltage of 3.0 V was calculated from the gradient between each discharge current and the battery voltage. And the output was calculated | required from the product of the electric current value in this lower limit voltage of 3.0V, and the voltage of 3.0V, and the value normalized with battery mass was made into the output density. All tests were performed in a test room controlled at a temperature of 20 ° C.

<Load characteristics>
Each battery was charged at a current value of 0.5 C to 4.2 V, and then discharged at a current value equivalent to 10 C (1000 mA) until it reached 3.0 V, and the discharge capacity (10 C discharge capacity) was measured. The load characteristics were measured in a test room controlled at a temperature of 20 ° C.

<Heating test>
Each battery was charged at a current value of 0.5 C up to 4.2 V in a test chamber controlled at a temperature of 20 ° C. Each battery in this charged state was placed in a thermostatic bath, the bath temperature was increased to 160 ° C. at a rate of 5 ° C./min, and the temperature was further maintained at 160 ° C. for 1 hour. The maximum temperature reached by the battery during the constant temperature operation at 160 ° C. for 1 hour after the start of temperature rise in the thermostat was measured with a thermocouple connected to the battery surface. The heating test was carried out with three batteries for each example and comparative example, and the reliability of the battery was evaluated based on the average value thereof.

  Table 1 shows the structure of the multilayer porous membrane and the heat shrinkage rate, and Table 2 shows the evaluation results of the cylindrical non-aqueous electrolyte secondary battery.

  In the batteries of Examples 1 to 8, both high power density of 1200 W / kg or more and high reliability in which the highest temperature reached only several degrees higher than the environmental temperature (160 ° C.) in the heating test can be achieved. ing. This is considered to be because the multilayer porous membrane used for the separator in each battery can achieve both high thermal stability and high ion permeability. Moreover, it can be said that the batteries of Comparative Examples 1 to 8 have a large 10C discharge capacity and good load characteristics.

  On the other hand, in the battery of Comparative Example 4 using a separator composed only of a resin porous film without providing a heat resistant porous layer, an increase in temperature is confirmed in the heating test. This is considered to be due to the thermal contraction or film breakage of the separator due to the battery being exposed to a high temperature. Moreover, since the part corresponded to the resin porous membrane which concerns on the multilayer porous membrane used for the separator is too thick, the output density is a low value.

Moreover, in the battery of Comparative Examples 1-3, the temperature rise to the heat runaway temperature vicinity of a positive electrode active material was confirmed in the heating test, and its reliability is inferior. In Comparative Example 3, although the heat shrinkage rate of the multilayer porous membrane is good, the result of the heating test is not good. This is because the resin porous membrane according to the separator is different from the resin porous membrane. When exposed to a high temperature above the melting point of the thermoplastic resin that constitutes it for a long time, most of the molten thermoplastic resin infiltrates into the heat-resistant porous layer, making it difficult to maintain an independent membrane structure and exposing the electrode. This is thought to be due to the result of this.

Claims (3)

A multilayer porous membrane comprising a heat-resistant porous layer containing heat-resistant fine particles as a main component, a thickness of 3 to 6 μm and a porosity of 55% or more, and a resin porous membrane containing a thermoplastic resin as a main component As
A non-aqueous electrolyte battery characterized in that the output density when the remaining capacity with respect to the full charge capacity is 50% is 1200 W / kg or more.   The non-aqueous electrolyte battery according to claim 1, wherein the heat-resistant fine particles contained in the heat-resistant porous layer have an aspect ratio of 1 to 3.   The nonaqueous electrolyte battery according to claim 1 or 2, wherein the heat-resistant fine particles contained in the heat-resistant porous layer are boehmite or alumina.