JP2008226566A - Composition for porous insulating layer formation, positive electrode for lithium-ion secondary battery, negative electrode for lithium ion secondary battery, and lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composition in order to form a porous insulating layer capable of improving resistance to short-circuiting of a lithium ion secondary battery on a surface of the positive electrode or the negative electrode for the lithium-ion secondary battery, the positive electrode and the negative electrode for the lithium ion secondary battery having the porous insulating layer formed by the composition, and the lithium ion secondary battery having the positive electrode or the negative electrode. <P>SOLUTION: By the composition for forming the porous insulating layer at least containing insulating particles having a heat resistant temperature of 150°C or more, poly N-vinyl acetamide, and a solvent, by the positive electrode for the lithium ion secondary battery and the negative electrode for the lithium ion secondary battery having the porous insulating layer formed with the porous insulating layer while using the composition for forming the porous insulating layer, and by the lithium ion secondary battery having at least one of the positive electrode for the lithium ion secondary battery and the negative electrode for the lithium ion secondary battery, problems are solved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery excellent in short circuit resistance, a positive electrode and a negative electrode for constituting the lithium ion secondary battery, and a composition for forming a porous insulating layer used for manufacturing these positive electrode and negative electrode It is about things.

  A lithium ion secondary battery, which is a type of nonaqueous electrolyte 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, the capacity of lithium ion secondary batteries tends to increase further, and ensuring safety is important.

  In the current lithium ion secondary battery, as a separator interposed between the positive electrode and the negative electrode, for example, a polyolefin microporous film having a thickness of about 20 to 30 μm is used. 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 a so-called shutdown function, 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 ensured by the above stretching. Therefore, the separator is distorted, and when it is exposed to a high temperature, there is a problem that shrinkage occurs due to residual stress. The shrinkage temperature is very close to the melting point, ie 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.

  From the viewpoint of increasing the capacity of a lithium ion secondary battery, for example, it is conceivable that the separator that does not participate in power generation is made thin so that the area in which the electrode can be accommodated in the battery is made larger. As the strength decreases, the workability during battery production is sufficiently secured, and further, in order to achieve sufficient separation between the positive electrode and the negative electrode in the battery, higher stretching is performed. It is necessary to increase the strength. As described above, the higher-stretched thin film separator has a higher degree of shrinkage when exposed to high temperatures. Therefore, in a battery using such a separator, when the internal temperature becomes abnormally high, The possibility of occurrence of a short circuit due to shrinkage becomes greater.

  For example, Patent Document 1 discloses a battery in which a porous protective film made of a resin binder and solid particles is formed on the surface of either a positive electrode active material coating layer of a positive electrode or a negative electrode active material coating layer of a negative electrode. Has been. The porous protective layer according to the battery disclosed in Patent Document 1 is intended to prevent the active material from falling off the electrode during battery production and prevent the occurrence of an internal short circuit. Depending on the configuration choice, this may increase the short circuit resistance of the battery.

Japanese Patent Laid-Open No. 7-220759

  Under the circumstances as described above, the present inventors tried to reduce the thickness of the separator, and in order to increase the short-circuit resistance of the battery that is reduced thereby, the heat resistance is good on at least one surface of the positive electrode and the negative electrode. Of a method to form a porous insulating layer containing various insulating particles was developed, and a battery with a high capacity was developed without the possibility of a short circuit even when the battery became hot and the separator contracted. It came to do. That is, if the positive electrode or the negative electrode having the porous insulating layer is used, even if the separator shrinks in the battery, the positive electrode mixture layer of the positive electrode and the negative electrode mixture layer of the negative electrode are formed by the porous insulating layer on the positive electrode or the negative electrode surface. Can be prevented.

  The porous insulating layer is formed by, for example, applying a composition formed by dispersing insulating particles and a binder in a solvent to the positive electrode mixture layer surface of the positive electrode or the negative electrode mixture layer surface of the negative electrode and drying. Can be formed.

  However, as a result of further investigation, in the composition for forming a porous insulating layer, for example, when insulating particles are agglomerated due to agglomeration of the insulating particles in the composition, It has been found that streaks or the like are generated in the conductive insulating layer, and the effect of improving the short circuit resistance of the battery by forming the porous insulating layer may not be sufficiently ensured. It is preferable to make the porous insulating layer as thin as possible from the viewpoint of preventing the battery capacity from decreasing. However, the thinner the porous insulating layer, the more dispersed the insulating particles in the composition for forming the porous insulating layer. The above problem due to badness becomes remarkable.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a porous insulating layer that can improve the short-circuit resistance of a lithium ion secondary battery on the surface of a positive electrode or a negative electrode for a lithium ion secondary battery. It is in providing the composition for forming, the positive electrode and negative electrode for lithium ion secondary batteries which have the porous insulating layer formed of this composition, and the lithium ion secondary battery which has the said positive electrode or negative electrode.

  The composition for forming a porous insulating layer of the present invention that has achieved the above object is a composition for forming a porous insulating layer on the surface of an electrode for a lithium ion secondary battery, and has a heat resistant temperature of 150. It contains at least insulating particles having a temperature of at least ° C., poly N-vinylacetamide, and a solvent.

  Further, the positive electrode for a lithium ion secondary battery of the present invention has a positive electrode mixture layer containing an active material on one side or both sides of a current collector, and the surface of the positive electrode mixture layer has a porous layer of the present invention. A negative electrode for a lithium ion secondary battery according to the present invention is provided on one side or both sides of a current collector, and has a porous insulating layer formed by using a composition for forming a conductive insulating layer. It has a negative electrode mixture layer containing a substance, and has a porous insulating layer formed on the surface of the negative electrode mixture layer using the porous insulating layer forming composition of the present invention. Is.

  In FIG. 1, the cross-sectional schematic diagram of an example of the positive electrode or negative electrode of this invention is shown. In the positive electrode or negative electrode 1 shown in FIG. 1, the positive electrode mixture layer or the negative electrode mixture layer 3 is formed on both surfaces of the positive electrode current collector or the negative electrode current collector 4, and the mixture on both sides of the current collector 4 is further formed. A porous insulating layer 2 is formed on the surface of the layer 3. In addition to the structure shown in FIG. 1, for example, the positive electrode or negative electrode of the present invention has a mixture layer (positive electrode mixture layer or negative electrode mixture layer) on both sides of the current collector, A structure having a porous insulating layer only on the surface of the mixture layer.

  Furthermore, the lithium ion secondary battery of the present invention is a battery provided with a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and is for the positive electrode for the lithium ion secondary battery of the present invention and the lithium ion secondary battery of the present invention. It has at least one of the negative electrodes.

  ADVANTAGE OF THE INVENTION According to this invention, the composition for porous insulating layer formation which can form the porous insulating layer which can improve the short circuit resistance of a lithium ion secondary battery favorable on the surface of a positive electrode or a negative electrode with favorable dispersion | distribution of insulating particles Can provide things. Moreover, according to the positive electrode for lithium ion secondary batteries and the negative electrode for lithium ion secondary batteries of this invention, the lithium ion secondary battery excellent in short circuit resistance can be provided. That is, the lithium ion secondary battery of the present invention is excellent in short circuit resistance.

  The composition for forming a porous insulating layer of the present invention comprises at least insulating particles having a heat-resistant temperature of 150 ° C. or higher (hereinafter sometimes simply referred to as “insulating particles”), poly N-vinylacetamide, and a solvent. (Slurry, paste, etc.). The porous insulating layer forming composition of the present invention is applied to the surface of the positive electrode mixture layer of the positive electrode for lithium ion secondary batteries or the negative electrode mixture layer of the negative electrode for lithium ion secondary batteries, and dried to remove the solvent. Thus, a porous insulating layer can be formed on the surface of the positive electrode or the negative electrode.

  The poly N-vinylacetamide in the composition for forming a porous insulating layer of the present invention has a function of suppressing the aggregation of the insulating particles in the composition for forming a porous insulating layer and dispersing them well. Therefore, according to the composition for forming a porous insulating layer of the present invention, a porous insulating layer (particularly a thin porous insulating layer) can be formed on the surface of the electrode mixture layer while suppressing the occurrence of defects such as streaks. Is possible. In addition, a lithium ion secondary battery using an electrode having a porous insulating layer has a positive electrode mixture layer of a positive electrode and a negative electrode mixture of a negative electrode formed by the porous insulating layer even when the inside of the battery becomes hot and the separator shrinks. Since contact with the agent layer can be prevented, it is excellent in short circuit resistance. In addition, poly N-vinylacetamide also has a function as a binder that binds the insulating particles to each other in the formed porous insulating layer.

  Insulating particles used in the composition for forming a porous insulating layer in order to constitute the porous insulating layer have a heat resistant temperature of 150 ° C. or more, have an electrical insulating property, and are electrochemically stable. In addition, any particles that are stable to the non-aqueous electrolyte and the solvent used for the composition for forming the porous insulating layer and that do not cause side reactions such as oxidation-reduction in the operating voltage range of the battery may be used. In this specification, “heat-resistant temperature is 150 ° C.” means that deformation such as softening is not observed at least at 150 ° C. 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 insulating particles include the following inorganic particles or organic particles, and these may be used alone or in combination of two or more. Examples of the inorganic particles (inorganic powder) include oxide particles such as iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), TiO ₂ , BaTiO ₂ , and ZrO; nitrides such as aluminum nitride and silicon nitride Particles: Slightly soluble ionic crystal particles such as calcium fluoride, barium fluoride and barium sulfate; Covalent crystal particles such as silicon and diamond; Clay particles such as montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, And materials derived from mineral resources such as olivine or artificial products thereof. Further, the surface of conductive particles such as metal particles; oxide particles such as SnO ₂ and tin-indium oxide (ITO); carbonaceous particles such as carbon black and graphite; Fine particles imparted with electrical insulation properties by surface treatment with a material constituting the above non-electrically conductive inorganic particles or a material constituting the crosslinked polymer particles described later) may be used. As organic particles (organic powder), various cross-links such as cross-linked polymethyl methacrylate, cross-linked polystyrene, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Polymer particles can be exemplified. The organic resin (polymer) constituting these organic particles is a mixture, modified product, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. It may be a polymer or a crosslinked product (in the case of thermoplastic polyimide).

  The shape of the insulating particles may be any of a spherical shape (including a true spherical shape and a substantially spherical shape), a rugby ball shape, and a plate shape. Examples of the plate-like insulating particles include plate-like boehmite and plate-like alumina.

  Of the insulating particles exemplified above, alumina particles are particularly preferable.

  The average particle size of the insulating particles is preferably 2 μm or less, and more preferably 1 μm or less. The porous insulating layer is preferably as thin as possible within a range that can ensure the effect, from the viewpoint of reducing the occupied volume of the porous insulating layer in the battery and increasing the capacity of the battery. If the average particle size of the particles is too large, it becomes difficult to form a thin porous insulating layer. If the insulating particles are too small, the specific surface area of the insulating particles increases, the amount of binder necessary to bind the insulating particles increases, and the heat resistance of the porous insulating layer decreases. Therefore, the average particle diameter of the insulating particles is preferably 0.1 μm or more, and more preferably 0.25 μm or more. In addition, the average particle diameter of the insulating particles referred to in this specification is the number measured by dispersing the fine particles in a medium that does not swell (for example, water) using a laser scattering particle size distribution diameter (“LA-920” manufactured by HORIBA). Average particle size.

  As described above, the poly N-vinylacetamide binds the insulating particles in the porous insulating layer together with the function of suppressing the aggregation of the insulating particles and dispersing them well in the composition for forming the porous insulating layer. However, a binder other than poly-N-vinylacetamide may be used for the porous insulating layer.

  As a binder other than poly-N-vinylacetamide used in the composition for forming a porous insulation layer for inclusion in the porous insulation layer, it is electrochemically stable and stable with respect to the non-aqueous electrolyte, Any material can be used as long as it can adhere the insulating particles satisfactorily. For example, ethylene-vinyl acetate copolymer (EVA, vinyl acetate-derived structural unit is 20 to 35 mol%), acrylic resin (ethylene-ethyl acrylate) Ethylene-acrylate copolymers such as copolymers), polyvinylidene fluoride (PVDF), fluorine-based rubber, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA) , Polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurea Emissions, such as epoxy resins. May use these alone or in combination of two or more. These binders may be dissolved in the solvent of the porous insulating layer forming composition or may be in the form of a dispersed emulsion.

  The solvent used in the composition for forming a porous insulating layer can uniformly disperse the insulating particles by using poly N-vinylacetamide, and when using a binder other than poly N-vinylacetamide, Any binder can be used as long as it can be dissolved or dispersed uniformly. Examples thereof include N-methyl-2-pyrrolidone (NMP); amides such as N, N-dimethylformamide and N, N-dimethylacetamide; Preferred are organic solvents such as sulfoxides; aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; among these, polar solvents [especially NMP, amides, dimethyl sulfoxide Etc.] has a high affinity with the coating film formed by the porous insulating layer forming composition Preferable from the. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when a binder other than poly-N-vinylacetamide is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol) may be used. , Ethylene glycol, etc.) can be added as appropriate to control the interfacial tension.

  The amount of poly N-vinylacetamide used in the composition for forming a porous insulating layer is insulative from the viewpoint of more effectively exerting the action (especially the dispersibility improving action of insulating particles) due to the use of poly N-vinylacetamide. The amount is preferably 1.5 parts by mass or more and more preferably 2 parts by mass or more with respect to 100 parts by mass of the particles. In addition, when the amount of organic matter in the porous insulating layer increases, resistance to lithium ion migration increases, and there is a concern that the discharge characteristics at a high rate (high rate) may decrease. The amount of poly N-vinylacetamide used in is preferably 10 parts by mass or less and more preferably 8 parts by mass or less with respect to 100 parts by mass of the insulating particles.

  In the composition for forming a porous insulating layer, when no binder other than poly N-vinylacetamide is used, in the porous insulating layer after formation, the insulating particles are bonded with poly N-vinylacetamide. From the viewpoint of exerting the adhesion effect more effectively, the amount of poly N-vinylacetamide used in the composition for forming a porous insulating layer is more preferably 3 parts by mass or more with respect to 100 parts by mass of the insulating particles. It is particularly preferably 5 parts by mass or more.

  In addition, when a binder other than poly-N-vinylacetamide is used in the composition for forming a porous insulating layer, the amount of poly-N-vinylacetamide used is determined according to the dispersibility of the insulating particles in the composition. For example, poly N-vinylacetamide in a composition for forming a porous insulating layer may be provided by suppressing the binding action between insulating particles in the porous insulating layer to the extent that an improving effect can be exhibited. Is preferably 6 parts by mass or less, more preferably 5 parts by mass or less with respect to 100 parts by mass of the insulating particles, and the discharge characteristics at a high rate of the battery due to an increase in the amount of organic substances in the porous insulating layer. You may make it suppress a fall. In this case, the amount of the binder other than poly-N-vinylacetamide used in the composition for forming a porous insulating layer is preferably 2 parts by mass or more, more preferably 3 parts by mass with respect to 100 parts by mass of the insulating particles. It is above, Preferably it is 8 mass parts or less, More preferably, it is 6 mass parts or less.

  The solid content concentration in the composition for forming a porous insulating layer (concentration of components other than insulating particles, binders other than poly-N-vinylacetamide and poly-N-vinylacetamide) is, for example, 70 to 80 mass. % Is preferable.

  The positive electrode for a lithium ion secondary battery of the present invention has a positive electrode mixture layer containing a positive electrode active material capable of occluding and releasing lithium ions on one side or both sides of a current collector, and further comprising the positive electrode mixture layer. The surface has a porous insulating layer formed using the composition for forming a porous insulating layer of the present invention.

Examples of the positive electrode active material include those used in conventionally known lithium ion secondary batteries, for example, Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, etc.). lithium-containing transition metal oxide is; LiMn ₂ O ₄ lithium-manganese oxide such _{as; LiMn x M (1-x} ) O 2 where a part of Mn of LiMn ₂ O ₄ was substituted with another element; olivine LiMPO ₄ (M: Co, Ni, Mn, Fe); LiMn _0.5 Ni _0.5 O ₂ ; Li _{(1 + a)} Mn _x Ni _y Co _(1-xy) O ₂ (−0.1 <a <0 .1, 0 <x <0.5, 0 <y <0.5); A positive electrode mixture in which a known conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these positive electrode active materials is finished into a molded body using the current collector as a core material. Thus, a positive electrode mixture layer can be provided on the surface of the current collector.

  As the composition of the positive electrode mixture layer, the content of the positive electrode active material is preferably 95 to 98% by mass, the content of the conductive auxiliary agent is preferably 0.5 to 3% by mass, and the binder. The content of is preferably 1-2% by mass. Moreover, it is preferable that the thickness (thickness per one side) of a positive mix layer is 60-160 micrometers.

  As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. 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 porous insulating layer-forming composition of the present invention is applied to the surface of the positive electrode mixture layer formed on the surface of the current collector and dried to form a porous insulating layer, thereby forming the positive electrode of the present invention. it can. The positive electrode mixture layer of the positive electrode is formed by applying a positive electrode mixture-containing composition (slurry, paste, etc.), in which a positive electrode mixture containing a positive electrode active material is dispersed in a solvent such as NMP, to a current collector and drying it. May be formed. When forming a porous insulating layer on the surface of the positive electrode mixture layer formed through such a manufacturing method, after coating on the current collector, on the positive electrode mixture containing composition before completely drying The positive electrode mixture layer and the porous insulating layer may be simultaneously formed by a method of applying and drying the porous insulating layer forming composition.

  The negative electrode for a lithium ion secondary battery of the present invention has a negative electrode mixture layer containing a negative electrode active material capable of occluding and releasing lithium ions on one side or both sides of a current collector, and further comprising the negative electrode mixture layer. The surface has a porous insulating layer formed using the composition for forming a porous insulating layer of the present invention.

  As the negative electrode active material, for example, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be occluded and released. One kind or a mixture of two or more kinds of carbon-based materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and their alloys, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. Then, a negative electrode mixture obtained by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials is finished into a molded body using the current collector as a core material. A negative electrode mixture layer can be formed on the current collector surface.

  As the composition of the negative electrode mixture layer, the content of the negative electrode active material is preferably 97 to 98% by mass, and the content of the binder is preferably 1 to 2% by mass. Moreover, when making a negative electrode mixture layer contain a conductive support agent, it is preferable that content of the conductive support agent in a negative mix layer is 1-2 mass%. Furthermore, the thickness of the negative electrode mixture layer (thickness per one side) is preferably 50 to 150 μm.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, 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.

  As with the lead portion on the positive electrode side, the lead portion on the negative electrode side usually leaves an exposed portion of the current collector without forming a negative electrode mixture layer on a part of the current collector during the preparation of the negative electrode. It is provided by making it a part. However, the lead portion on the negative electrode side is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.

  The porous insulating layer forming composition of the present invention is applied to the surface of the negative electrode mixture layer formed on the surface of the current collector and dried to form a porous insulating layer, whereby the negative electrode of the present invention can be obtained. it can. The negative electrode mixture layer of the negative electrode is obtained by applying a negative electrode mixture-containing composition (slurry, paste, etc.) in which a negative electrode mixture containing a negative electrode active material is dispersed in a solvent such as NMP to a current collector and drying it. May be formed. When forming a porous insulating layer on the surface of the negative electrode mixture layer formed through such a manufacturing method, after coating on the current collector, on the negative electrode mixture containing composition before completely drying The negative electrode mixture layer and the porous insulating layer may be formed at the same time by a method in which a composition for forming a porous insulating layer is applied and dried.

  In both the positive electrode of the present invention and the negative electrode of the present invention, the thickness of the porous insulating layer is the same as that of the positive electrode mixture layer of the positive electrode when the separator contracts in the battery. From the viewpoint of more effectively exerting the effect of preventing the contact of the negative electrode with the negative electrode mixture layer), it is preferably 1 μm or more, and more preferably 2 μm or more. Moreover, from the viewpoint of reducing the occupied volume of the porous insulating layer in the battery and suppressing the capacity reduction of the battery, the thickness of the porous insulating layer is 8 μm in both the positive electrode of the present invention and the negative electrode of the present invention. Or less, and more preferably 6 μm or less.

  In either the positive electrode of the present invention or the negative electrode of the present invention, when the porous insulating layer does not contain a binder other than poly N-vinylacetamide, the poly N-vinylacetamide in the porous insulating layer The content is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, with respect to 100 parts by mass of the insulating particles.

  In both the positive electrode of the present invention and the negative electrode of the present invention, when the porous insulating layer contains a binder other than poly N-vinylacetamide, the poly N-vinyl in the porous insulating layer is used. The content of acetamide is preferably 1.5 parts by mass or more, more preferably 2 parts by mass or more, preferably 6 parts by mass or less, more preferably 5 parts by mass or less, with respect to 100 parts by mass of the insulating particles. The content of the binder other than poly N-vinylacetamide in the porous insulating layer is preferably 2 parts by mass or more, more preferably 3 parts by mass or more with respect to 100 parts by mass of the insulating particles. The amount is preferably 8 parts by mass or less, more preferably 6 parts by mass or less.

  The lithium ion secondary battery of the present invention has at least one of the positive electrode for a lithium ion secondary battery of the present invention and the negative electrode for a lithium ion secondary battery of the present invention. That is, in the battery of the present invention, the electrode having a porous insulating layer may be a positive electrode or a negative electrode. Moreover, both the positive electrode and the negative electrode may have a porous insulating layer. Furthermore, the positive electrode of the present invention having a positive electrode mixture layer on both sides of the current collector and a porous insulating layer on the surface of the positive electrode mixture layer on one side, and a negative electrode mixture layer on both sides of the current collector And using the negative electrode of the present invention having a porous insulating layer on the surface of the negative electrode mixture layer on one side, the positive electrode and the negative electrode are overlapped so that the porous insulating layer is always interposed between the positive electrode and the negative electrode. May be used.

  In addition, when using the positive electrode or negative electrode which does not have a porous insulating layer for the battery of this invention, the positive electrode of the structure which remove | excluded the porous insulating layer from the positive electrode of this invention shown previously, or this invention shown previously. A negative electrode having a configuration in which the porous insulating layer is removed from the negative electrode can be used.

  The separator according to the battery of the present invention is a uniaxially stretched microporous film employed in a conventionally known lithium ion secondary battery, that is, a film formed by adding an inorganic filler to the constituent resin of the film. Alternatively, a separator made of a microporous film in which holes are formed by biaxial stretching can be applied.

  As resin which comprises the microporous film used as a separator, polyolefin, such as polyethylene (PE) and polypropylene (PP), etc. are mentioned, for example.

  The thickness of the separator used in the battery of the present invention is not particularly limited. For example, the sum of the total thickness of the positive electrode and the total thickness of the negative electrode (porous insulation) is the same as that of a conventionally known lithium ion secondary battery. The thickness of the layer is also included (the same applies to the thickness of the separator), and a separator having a thickness of 10% or less (for example, 7%) can be used. Since the short-circuit resistance is enhanced by the presence of the conductive insulating layer, it is possible to use a separator that is thinner and has a higher degree of thermal shrinkage than that employed in a conventionally known lithium ion secondary battery. It is also possible to increase the capacity by making the electrode thicker. Specifically, the thickness of the separator can be preferably 5% or less, more preferably 3% or less with respect to the total thickness of the positive electrode and the total thickness of the negative electrode. However, if the separator is too thin, it is difficult to ensure sufficient strength at the time of manufacturing the battery and sufficient strength in the battery. Therefore, the thickness is preferably 8 μm or more.

  Moreover, it is preferable that the porosity of a separator is 30 to 70%.

  The lithium ion secondary battery of the present invention can be formed, for example, by laminating a positive electrode and a negative electrode with a separator interposed therebetween so that a porous insulating layer is interposed between the positive electrode and the negative electrode. Is wound to form a wound electrode body. After inserting such an electrode body into the exterior body, a non-aqueous electrolyte is injected, and then the exterior body is sealed.

  There is no restriction | limiting in particular as an exterior body of a battery, The steel can, aluminum can, etc. of the cylinder shape (square tube shape, cylindrical shape, etc.) employ | adopted as a conventionally well-known lithium ion secondary battery are mentioned. In addition, a laminate film obtained by vapor-depositing a metal on a resin film can be used for the exterior body.

Examples of the non-aqueous electrolyte include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1, 3-dioxolane, tetrahydrofuran, 2-methyl - tetrahydrofuran, one composed of only an organic solvent such as diethyl ether or a mixture of two or more solvents, for _{example, 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 ≧ ), LiN (RfOSO ₂₎ those ₂ [here Rf of fluoroalkyl group] was prepared by dissolving at least one selected from lithium salts such as are used. The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  In addition, non-aqueous electrolytes include esters with double bonds such as vinylene carbonate; sulfur-containing organic compounds such as propane sultone; fluorine-containing fluorine such as fluorobenzene for the purpose of improving charge / discharge cycle characteristics and load characteristics of the battery. It is preferable to add additives such as aromatic compounds.

  The lithium ion secondary battery of this invention can be used for the same use as the various uses to which a conventionally well-known lithium ion secondary battery is applied.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

Example 1
<Preparation of slurry for forming porous insulating layer>
100 parts by mass of alumina particles having an average particle size of 0.5 μm, 90 parts by mass of NDF solution of PVDF (“PVDF # 9305” manufactured by Kureha Chemical Co., Ltd., solid concentration 5% by mass), NMP solution of poly N-vinylacetamide (Showa) 100 parts by mass of “GE-191” manufactured by Denko Co., Ltd., solid content concentration of 5% by mass) and 84 parts by mass of NMP were mixed and made into a paint with a bead disperser to prepare a slurry for forming a porous insulating layer. . The amount of poly N-vinylacetamide in the obtained composition for forming a porous insulating layer is 5 parts by mass with respect to 100 parts by mass of alumina particles, and the amount of PVDF is 4. 5 parts by mass.

<Production of negative electrode>
Graphite-based carbon material (A) as a negative electrode active material [purity 99.9% or more, average particle diameter 18 μm, inter-surface distance (d ₀₀₂ ) = 0.3356 nm, crystallite size in the c-axis direction (Lc ) = 100 nm, R value (ratio of peak intensity around ₁₃₅₀ cm ⁻¹ and peak intensity around 1580 cm ⁻¹ in the Raman spectrum when excited by an argon laser with a wavelength of 514.5 nm [R = I ₁₃₅₀ / I ₁₅₈₀ ] ) = 0.18] 70 parts by mass and graphite-based carbon material (B) [purity 99.9% or more, average particle diameter 21 μm, d ₀₀₂ = 0.3363 nm, Lc = 60 nm, R value = 0.11] 30 The mixture was mixed with 98 parts by mass of this mixture, and 1 part by mass of CMC and 1 part by mass of SBR in the presence of water to prepare a slurry-like negative electrode mixture-containing paste. The obtained negative electrode mixture-containing paste was applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried to form a negative electrode mixture layer, and the density of the negative electrode mixture layer was 1. A pressure treatment was performed until the pressure became 65 g / cm ^3, and after cutting into a predetermined size, a nickel lead was welded to prepare a negative electrode. The thickness of the negative electrode mixture layer of the obtained negative electrode was 60 μm per side, and the total thickness of the negative electrode was 130 μm.

  The porous insulating layer forming slurry was applied to the surface of the negative electrode mixture layer on both surfaces of the negative electrode by a slot die method, and dried to form a porous insulating layer having a thickness of 5 μm per side.

<Preparation of positive electrode>
97.3 parts by mass of lithium cobaltate and 1.5 parts by mass of a carbon material as a conductive auxiliary agent are put into a quantitative feeder which is a powder feeder, and an NMP solution of PVDF (manufactured by Kureha Chemical Co., Ltd.). “L # 1120”, solid content concentration of 12% by mass) is adjusted so that the solid content concentration during kneading is always 94% by mass so that a predetermined input amount per unit time is obtained. The mixture was fed into a twin-screw kneading extruder while being kneaded to prepare a positive electrode mixture-containing paste. The obtained positive electrode mixture-containing paste was put into a planetary mixer, diluted with the same PVDF NMP solution and NMP as described above, and adjusted to a coatable viscosity. The solid content concentration of the positive electrode mixture-containing paste after dilution was 73.0% by mass. The diluted positive electrode mixture-containing paste is passed through a 70-mesh net to remove large inclusions, and then uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 15 μm and dried to form a film. A positive electrode mixture layer was formed. The solid content ratio of the positive electrode mixture layer after drying is 97.3: 1.5: 1.2 in terms of mass ratio of positive electrode active material: conductive auxiliary agent: PVDF. Then, after pressurizing and cutting to a predetermined size, an aluminum lead body was welded to produce a sheet-like positive electrode. The density of the positive electrode mixture layer after the pressure treatment (positive electrode density) was 3.8 g / cm ³ , the thickness of the positive electrode mixture layer was 60 μm per side, and the total thickness of the positive electrode was 135 μm.

<Battery assembly>
After drying the positive electrode and the negative electrode, they are stacked through a separator made of a microporous PE film having a thickness of 12 μm, wound in a spiral shape, and then crushed into a flat wound electrode body, which is an aluminum alloy. Inserted into a rectangular battery case made of metal, welded positive and negative electrode lead bodies and laser welded to the opening end of the cover plate to the battery case, the above non-aqueous electrolysis from the inlet provided in the sealing cover plate After injecting the solution into the battery case and fully infiltrating the non-aqueous electrolyte into the separator, etc., partial charging was performed, and after the gas generated by partial charging was discharged, the inlet was sealed and sealed. . Thereafter, charging and aging are performed, the structure shown in FIG. 2 has the appearance shown in FIG. 3, the width is 34.0 mm, the thickness is 4.0 mm, and the height is 50.0 mm. A lithium ion secondary battery was obtained. The non-aqueous electrolyte includes a mixed solvent of methyl ethyl carbonate, diethyl carbonate and ethylene carbonate having a mixing ratio of 1.5 / 0.5 / 1.0 (volume ratio) and LiPF ₆ of 1.2 mol / What was dissolved in 1 was used.

  Here, the battery shown in FIGS. 2 to 3 will be described. The positive electrode 10 and the negative electrode 20 are wound in a spiral shape with the separator 30 interposed therebetween and the porous insulating layer of the negative electrode 20 interposed therebetween as described above. The wound electrode body 60 is accommodated in a rectangular battery case 40 together with a non-aqueous electrolyte. However, in FIG. 2, in order to avoid complication, a metal foil or a non-aqueous electrolyte as a current collector used in the production of the positive electrode 10 and the negative electrode 20, a porous insulating layer formed on the negative electrode mixture layer surface of the negative electrode 20 Etc. are not shown.

  The battery case 40 is made of an aluminum alloy and constitutes the main part of the battery exterior material. The battery case 40 also serves as a positive electrode terminal. An insulator 50 made of a polytetrafluoroethylene sheet is disposed at the bottom of the battery case 40. From the wound electrode body 60 made of the positive electrode 10, the negative electrode 20, and the separator 30, one end of each of the positive electrode 10 and the negative electrode 20 is provided. The positive electrode lead body 70 and the negative electrode lead body 80 connected to each other are drawn out. A stainless steel terminal 110 is attached to the aluminum lid plate 90 that seals the opening of the battery case 40 via a polypropylene insulating packing 100, and the terminal 110 is made of stainless steel via an insulator 120. A steel lead plate 130 is attached.

  And this cover plate 90 is inserted in the opening part of the said battery case 40, and the opening part of the battery case 40 is sealed by welding the junction part of both, and the inside of a battery is sealed. Further, in the battery of FIG. 2, an electrolyte solution inlet 140 is provided in the cover plate 90, and the electrolyte solution inlet 140 is welded and sealed by, for example, laser welding in a state where a sealing member is inserted. Thus, the sealing property of the battery is ensured (therefore, in the batteries of FIGS. 2 and 3, the electrolyte inlet 140 is actually the electrolyte inlet and the sealing member, but the explanation is easy. In order to achieve this, it is shown as an electrolyte inlet 140). Furthermore, the cover plate 90 is provided with an explosion-proof vent 150.

  In the battery of Example 1, the battery case 40 and the cover plate 90 function as positive terminals by directly welding the positive electrode lead body 70 to the cover plate 90, and the negative electrode lead body 80 is welded to the lead plate 130. The negative electrode lead body 80 and the terminal 110 are electrically connected via the lead plate 130 so that the terminal 110 functions as a negative electrode terminal. However, depending on the material of the battery case 40, the sign may be reversed. There is also.

  FIG. 3 is a perspective view schematically showing the external appearance of the battery shown in FIG. 2. This FIG. 3 is shown for the purpose of showing that the battery is a square battery. Fig. 1 schematically shows a battery, and shows a specific battery component.

Example 2
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the amount of poly N-vinylacetamide in the slurry for forming the porous insulating layer was 6 parts by mass with respect to 100 parts by mass of the alumina particles.

Example 3
A lithium ion secondary battery is produced in the same manner as in Example 1 except that the amount of poly N-vinylacetamide in the slurry for forming the porous insulating layer is 1.5 parts by mass with respect to 100 parts by mass of the alumina particles. did.

Example 4
The slurry for forming a porous insulating layer prepared in the same manner as in Example 1 was applied to the surface of the positive electrode mixture layer on both surfaces of the positive electrode prepared in the same manner as in Example 1 by the slot die method, dried, A porous insulating layer having a thickness of 5 μm was formed.

  A lithium ion secondary battery was produced in the same manner as in Example 1 except that the above positive electrode and a negative electrode produced in the same manner as in Example 1 were used except that the porous insulating layer was not formed.

Example 5
A lithium ion secondary battery was produced in the same manner as in Example 4 except that the porous insulating layer forming slurry prepared in the same manner as in Example 3 was used.

Example 6
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the thickness of the porous insulating layer was 3 μm per side of the negative electrode.

Example 7
A slurry for forming a porous insulating layer prepared in the same manner as in Example 1 was used except that PVDF was not used and the amount of poly N-vinylacetamide was changed to 7 parts by mass with respect to 100 parts by mass of alumina particles. A lithium ion secondary battery was produced in the same manner as in Example 1 except for the above.

Example 8
A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the thickness of the porous insulating layer was 8 μm per one side of the negative electrode.

Example 9
Except for using alumina particles having an average particle diameter of 0.25 μm, a slurry for forming a porous insulating layer prepared in the same manner as in Example 1 was used, and the thickness of the porous insulating layer was 2 μm per one side of the negative electrode Produced a lithium ion secondary battery in the same manner as in Example 1.

Example 10
Except for using alumina particles having an average particle size of 0.2 μm, a slurry for forming a porous insulating layer prepared in the same manner as in Example 1 was used, and the thickness of the porous insulating layer was 8 μm per side of the negative electrode Produced a lithium ion secondary battery in the same manner as in Example 1.

Comparative Example 1
A slurry for forming a porous insulating layer was prepared in the same manner as in Example 1 except that no poly N-vinylacetamide was added, and the same procedure as in Example 1 was performed except that this slurry for forming a porous insulating layer was used. Thus, a lithium ion secondary battery was produced.

Comparative Example 2
A lithium ion secondary battery was produced in the same manner as in Example 5 except that the slurry for forming a porous insulating layer prepared in the same manner as in Comparative Example 1 was used.

Comparative Example 3
A lithium ion secondary battery was produced in the same manner as in Example 1 except that no porous insulating layer was formed on either the positive electrode or the negative electrode.

  Surface appearance evaluation of the porous insulating layer on the electrode surface produced in Examples 1 to 10 and Comparative Examples 1 to 2, and the batteries of Examples 1 to 10 and Comparative Examples 1 to 3 were evaluated for charge / discharge rate characteristics and high-temperature storage. Tests were conducted. The results are shown in Table 1.

<Evaluation of surface appearance of porous insulating layer>
The surface state of the porous insulating layer on the negative electrode or the positive electrode surface prepared in Examples 1 to 10 and Comparative Examples 1 to 2 was visually observed to check for defects such as coating stripes and pinholes.

<Evaluation of battery charge / discharge rate characteristics>
The lithium ion secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 3 were charged at a constant current of 0.2 C up to 4.2 V and then charged at a constant voltage of 4.2 V until the total charging time was 8 hours. Subsequently, constant current discharge was performed until the battery voltage became 3.0 V at 0.2 C, and the discharge capacity (A) was obtained. Thereafter, constant current discharge was performed again until the battery voltage reached 3.0 V at 2C after charging under the same conditions, and the discharge capacity (B) was determined. The ratio of the discharge capacity (B) to the discharge capacity (A) was expressed as a percentage and used as the charge / discharge rate characteristic value.

<High-temperature battery storage test>
10 batteries of Examples 1 to 10 and Comparative Examples 1 to 3 were prepared, and after charging with a constant current of 0.2 C to 4.2 V, they were charged with a constant voltage until the total charging time was 8 hours. . Thereafter, these batteries were stored in a thermostat kept at 130 ° C. for 2 hours, cooled to room temperature, and then the battery voltage was measured to examine the number of batteries having a voltage of 3.0 V or less.

  In Table 1, the “number of voltage drops” in the column of the high temperature storage test means the number of batteries whose battery voltage is 3.0 V or less in the high temperature storage test.

  As is clear from Table 1, in the porous insulating layer according to the negative electrode or the positive electrode of Examples 1 to 10 formed using the slurry for forming a porous insulating layer prepared by adding poly N-vinylacetamide, the above slurry The dispersion of alumina particles therein is good, so there are no appearance defects such as streaks and pinholes due to the influence of aggregates, and the lithium secondary batteries of Examples 1 to 10 using such a negative electrode or positive electrode In this case, the insulation between the positive and negative electrodes can be maintained even when the separator contracts during the high-temperature storage test, and excellent short-circuit resistance is exhibited. Therefore, the batteries of Examples 1 to 10 have excellent safety such that heat is generated by an internal short circuit or the like, and even if the separator contracts due to this heat, the presence of the porous insulating layer can prevent the expansion of the short circuit. It can be said.

It is a cross-sectional schematic diagram which shows an example of the positive electrode for lithium ion secondary batteries or the negative electrode for lithium ion secondary batteries of this invention. It is a figure which shows typically an example of the lithium ion secondary battery of this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. FIG. 3 is a perspective view of the lithium ion secondary battery shown in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode for lithium ion secondary batteries or negative electrode for lithium ion secondary batteries 2 Porous insulating layer 3 Positive electrode mixture layer or negative electrode mixture layer 4 Positive electrode current collector or negative electrode current collector

Claims (8)

A porous insulating layer forming composition for forming a porous insulating layer on the surface of a lithium ion secondary battery electrode,
A composition for forming a porous insulating layer, comprising at least insulating particles having a heat-resistant temperature of 150 ° C. or more, poly N-vinylacetamide, and a solvent.   The composition for forming a porous insulating layer according to claim 1, wherein the insulating particles having a heat resistant temperature of 150 ° C or higher have an average particle diameter of 0.1 to 2 µm.   The composition for forming a porous insulating layer according to claim 1 or 2, wherein the insulating particles having a heat resistant temperature of 150 ° C or higher are alumina particles.   The porous insulating layer formation according to any one of claims 1 to 3, comprising 1.5 to 10 parts by mass of poly-N-vinylacetamide with respect to 100 parts by mass of insulating particles having a heat resistant temperature of 150 ° C or higher. Composition.   The composition for forming a porous insulating layer according to any one of claims 1 to 4, further comprising a binder other than poly N-vinylacetamide.   It has the positive mix layer containing an active material in the single side | surface or both surfaces of a collector, The composition for porous insulation layer formation in any one of Claims 1-5 on the surface of the said positive mix layer A positive electrode for a lithium ion secondary battery, comprising a porous insulating layer formed using a material.   It has the negative mix layer containing an active material in the single side | surface or both surfaces of a collector, The composition for porous insulating layer formation in any one of Claims 1-5 on the surface of the said negative mix layer A negative electrode for a lithium ion secondary battery, comprising a porous insulating layer formed using a material. A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
A lithium ion secondary battery comprising at least one of the positive electrode for a lithium ion secondary battery according to claim 6 and the negative electrode for a lithium ion secondary battery according to claim 7.

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