JP2014022245A - Lithium ion secondary battery and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery in which variation in battery thickness is restrained and which excels in safety and has excellent load characteristic, and a manufacturing method thereof.SOLUTION: The lithium ion secondary battery comprises a wound electrode body whose cross section is flat-shaped and a nonaqueous electrolyte, in which a cathode has a current collection tab fitted to the exposed section thereof where a cathode mixture layer is nonexistent in at least part of a current collector, an anode has a current collection tab fitted to the exposed section thereof where an anode mixture layer is nonexistent in at least part of a current collector, and a separator has a porous layer (I) composed of polyolefin microporous film and a porous layer (II) containing, as its main constituent, inorganic particles whose heatproof temperature is 150°C or higher. In the wound electrode body, the porous layer (I) of the separator and the cathode and/or anode are stuck together, and the thinnest section of the separator is 80 to 95% in thickness of the thickest section thereof.

Description

  The present invention relates to a lithium ion secondary battery in which variations in battery thickness are suppressed, safety and load characteristics are good, and a manufacturing method thereof.

  In recent years, the importance of mobile devices (portable devices) such as mobile phones, PDAs, and notebook personal computers has increased, and the importance of batteries mounted thereon has also increased. In particular, due to environmental considerations, the importance of lithium ion secondary batteries that can be repeatedly charged is increasing.

  As a lithium ion secondary battery applied to such applications, for example, an electrode body formed by laminating a positive electrode and a negative electrode via a separator and then spirally winding the electrode body to have a flat cross section, There are known thin and small-sized ones that are housed together with a non-aqueous electrolyte inside a thin exterior body such as a rectangular battery can.

  In addition, lithium ion secondary batteries have higher capacities, improved various battery characteristics (for example, charge / discharge cycle characteristics), and higher capacities as the application devices become more functional. There is a demand for improved safety.

  With regard to improving the safety of lithium ion secondary batteries, for example, Patent Document 1 and Patent Document 2 describe a resin porous layer (I) for ensuring shutdown characteristics and a heat resistant porous material for improving the heat resistance of a separator. In an electrochemical element such as a lithium ion secondary battery provided with a separator having a layer (II), the heat resistant porous layer (II) contains an adhesive resin that exhibits adhesiveness at a relatively low heating temperature, A technique for integrating at least one of a positive electrode and a negative electrode with a separator has been proposed.

  Further, in Patent Document 3, the variation of the thickness of the separator is set within a specific range in the flat wound electrode body, so that the uniformity of the charge / discharge reaction in the electrode body is improved, and the charge / discharge cycle characteristics of the battery are disclosed. Techniques for improving the quality have been proposed.

JP 2011-23186 A JP 2011-54503 A JP 2003-297429 A

  By the way, the lithium ion secondary battery is usually completed through a process of precharging (chemical conversion treatment) before or after sealing the outer package after housing the electrode body and the non-aqueous electrolyte in the outer package. Shipped. Since the electrode body expands due to the volume change of the negative electrode during the preliminary charging, when a large number of batteries are manufactured, the thickness of each battery may vary.

  Even with variations in the thickness of lithium ion secondary batteries that occur during manufacturing, which was not at a level that has been regarded as a problem in the past, the devices themselves to which lithium ion secondary batteries of the above-mentioned thin and small forms are applied are thinned. It is expected that it will be unacceptable due to the progress of miniaturization and the development of technology that can sufficiently respond to such severe demands. In addition, when a negative electrode active material having a large capacity is used, there is a risk that variations in the thickness of the lithium ion secondary battery generated during production may increase. A technique for suppressing variation is useful.

  The techniques described in Patent Documents 1 and 2 are sufficiently capable of, for example, ensuring safety that is required as the capacity of a battery increases, and are also capable of suppressing variation in thickness during battery manufacture. Although effective, there is still room for improvement.

  In addition, the technique described in Patent Document 3 may contribute to the suppression of thickness variation during battery manufacture in terms of controlling the thickness of the separator in the electrode body, but safety corresponding to the increase in capacity. There is room for improvement in securing.

  The present invention has been made in view of the above circumstances, and the object thereof is a lithium ion secondary battery in which variation in battery thickness is suppressed, safety is excellent, and load characteristics are good, and a manufacturing method thereof, Is to provide.

  The lithium ion secondary battery of the present invention that has achieved the above object is a positive electrode having a positive electrode mixture layer containing a positive electrode active material on one or both sides of a current collector, and a negative electrode mixture layer containing a negative electrode active material A negative electrode having a negative electrode on one or both sides of a current collector and a lithium ion secondary having a spirally wound electrode body having a flat cross section wound in a spiral shape and a non-aqueous electrolyte The positive electrode has a current collector tab attached to an exposed portion where the positive electrode mixture layer is not present in at least a part of the current collector, and the negative electrode is a negative electrode composite in at least a part of the current collector. A current collecting tab is attached to the exposed portion where the agent layer does not exist, and the separator is mainly composed of a porous layer (I) composed of a microporous membrane made of polyolefin and inorganic fine particles having a heat resistant temperature of 150 ° C. or more. Porous layer containing as (II) In the wound electrode body, the porous layer (I) of the separator is bonded to the positive electrode and / or the negative electrode, and the thinnest portion of the separator is thickest. It is characterized by being 80 to 95% of the thickness.

  The lithium ion secondary battery of the present invention includes a step (1) of forming a wound electrode body by winding a laminate in which a separator is disposed between a positive electrode and a negative electrode, and heating and pressing the wound electrode body The step (2) of attaching the porous layer (I) of the separator and the positive electrode and / or the negative electrode while flattening the cross section is performed, and the heating press in the step (2) is performed. It can manufacture by the manufacturing method of this invention characterized by implementing on the conditions of the temperature of 40-70 degreeC, and the pressure of 1.96-9.80 MPa.

  According to the present invention, it is possible to provide a lithium ion secondary battery in which variation in battery thickness is suppressed, safety is excellent, and load characteristics are good, and a manufacturing method thereof.

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. It is a perspective view of the lithium ion secondary battery shown in FIG.

The lithium ion secondary battery of the present invention has a wound electrode body with a flat cross section (hereinafter sometimes referred to as a “flat wound electrode body”). As a separator interposed between the anode and the anode, a porous layer (I) composed of a microporous membrane made of polyolefin and a porous layer (II) mainly containing inorganic fine particles having a heat resistant temperature of 150 ° C. or more The separator has a porous layer (I) and a positive electrode and / or a negative electrode. In the flat wound electrode body, the thickness of the thinnest part of the separator is 80% to 95% of the thickness of the thickest part, that is, the thickness of the thinnest part of the separator is a (μm), When the thickness of the thick part is b (μm), the value of X obtained by the following formula is 80% or more and 95% or less.
X = 100 × (a / b)

  A spirally wound electrode body having a flat cross section is usually formed by laminating a positive electrode and a negative electrode via a separator, and winding this into a spiral shape to form a wound electrode body, and then applying a press treatment to the wound electrode body. It is manufactured through a process of crushing the electrode body. In that case, the separator used for the wound electrode body is deformed by the press stress, and the thickness is reduced.

  The degree of deformation of the separator after the press treatment is 80% or more and 95% or less in the value of X, and the degree to which the porous layer (I) of the separator and the electrode (positive electrode and / or negative electrode) stick When the flat spirally wound electrode body is used, the reason is not clear, but it is possible to satisfactorily suppress variations in the thickness of each battery immediately after the manufacture of a large number of lithium ion secondary batteries.

  The degree of sticking between the separator porous layer (I) and the electrode in the flat wound electrode body according to the lithium ion secondary battery of the present invention is, for example, such that the separator and the electrode can be peeled by hand. The case where it is stuck is included.

  In addition, the separator causes a shutdown when the battery becomes high temperature, the thermal shrinkage is suppressed, and the porous layer (I) of the separator is attached to the electrode. Thermal shrinkage is further suppressed. Therefore, the lithium ion secondary battery of the present invention has good safety (especially safety when the temperature inside the battery becomes abnormally high).

  The separator according to the lithium ion secondary battery of the present invention includes a porous layer (I) composed of a microporous membrane made of polyolefin and a porous layer (II) mainly comprising inorganic fine particles having a heat resistant temperature of 150 ° C. or higher. And have.

  The porous layer (I) according to the separator has an original function of preventing a short circuit between the positive electrode and the negative electrode and a function as a support for the porous layer (II) described later. Further, as will be described later, the porous layer (I) can ensure a shutdown function [for example, a property that the pores of the separator are blocked at 80 ° C. or higher (more preferably 100 ° C. or higher) 150 ° C. or lower]. . That is, when the temperature of the lithium ion secondary battery of the present invention reaches or exceeds the melting point of the polyolefin constituting the porous layer (I), the polyolefin melts to close the pores of the separator, and the electrochemical reaction proceeds. Causes a shutdown to be suppressed.

  Further, the porous layer (I) is adhered to the electrode (positive electrode and / or negative electrode) while being deformed in the pressing step (heat pressing step) at the time of forming the flat wound electrode body.

  Examples of the polyolefin relating to the microporous membrane made of polyolefin constituting the porous layer (I) include polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymer.

  The microporous membrane made of polyolefin may have a single-layer structure constituted by the above-exemplified polyolefin, or may have a multilayer structure. Examples of the microporous film having a multilayer structure include a microporous film having a two-layer structure having a PE layer and a PP layer; a microporous film in which PE layers / PP layers / PE layers are sequentially laminated, and a PP layer For example, a microporous membrane having a three-layer structure such as a microporous membrane formed by sequentially laminating / PE layer / PP layer.

  The microporous membrane constituting the porous layer (I) is a differential scanning calorimeter (DSC) according to the melting point, that is, according to JIS K 7121, from the viewpoint of ensuring a better shutdown function of the separator. It is preferable to contain a polyolefin having a melting temperature of 80 ° C. or higher and 150 ° C. (more preferably 100 ° C. or higher), more specifically PE.

  In addition, since PP has higher oxidation resistance than PE, PP is preferably present on the surface of the microporous film constituting the porous layer (I) from the viewpoint of enhancing the oxidation resistance of the separator. . As a microporous film having PP on the surface, a microporous film composed of only a PP layer, or a microporous film having a three-layer structure composed of PP layer / PE layer / PP layer sequentially laminated ( And a microporous membrane having a three-layer structure having PP layers on both sides of the PE layer).

  Therefore, since the shutdown function of the separator can be better secured while enhancing the oxidation resistance of the separator, the microporous film constituting the porous layer (I) is formed by sequentially stacking PP layer / PE layer / PP layer. A microporous membrane having a three-layer structure is particularly preferable. In the case of the three-layer microporous film, the thickness of the PP layer is preferably 2 to 8 μm, and the thickness of the PE layer is preferably 2 to 10 μm.

  In the case where the porous layer (I) is composed of a thermoplastic resin having a melting point of 80 ° C. or more and 150 ° C. or less like PE and a thermoplastic resin having a melting point exceeding 150 ° C. like PP. For example, a microporous film formed by mixing PE and a resin having a higher melting point than PE such as PP is used as a porous layer (I), or has a higher melting point than PE such as a PE layer and a PP layer. When the porous layer (I) is a multi-layered microporous film formed by laminating a layer composed of the above resin, the melting point in the thermoplastic resin constituting the porous layer (I) The resin (for example, PE) having a temperature of 80 ° C. or higher and 150 ° C. or lower is preferably 20% by mass or more, and more preferably 30% by mass or more.

  Further, the porous layer (I) may contain a filler or the like in order to improve the strength and the like within a range that does not impair the action of imparting the shutdown function to the separator. Examples of the filler that can be used for the porous layer (I) include the same inorganic fine particles (inorganic fine particles having a heat resistant temperature of 150 ° C. or higher) that can be used for the porous layer (II) described later.

The particle diameter of the filler is an average particle diameter, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 10 μm or less, preferably 1 μm or less. More preferred. In addition, the average particle diameter of the various particles referred to in the present specification [the filler, inorganic fine particles according to the porous layer (II) described later, active material particles of positive and negative electrodes) is, for example, a laser scattering particle size distribution meter (for example, D _50% (particle diameter at a volume-based cumulative fraction of 50%) measured by dispersing these fillers in a medium that does not dissolve the fillers using “LA-920” manufactured by HORIBA, Ltd.

  The content of the thermoplastic resin in the porous layer (I) is preferably as follows to make it easier to obtain a shutdown effect, for example. The volume content of the polyolefin in the total volume of the constituent components of the porous layer (I) (in the total volume of all the constituent components excluding the pores) is preferably 50% by volume or more, and 70% by volume or more. More preferably, it may be 100% by volume. Furthermore, the porosity of the porous layer (II) required by the method described later is 20 to 60%, and the volume of the polyolefin related to the porous layer (I) is the pore volume of the porous layer (II). It is preferable that it is 50% or more.

  The porous layer (II) according to the separator has a function of preventing a short circuit due to direct contact between the positive electrode and the negative electrode even when the internal temperature of the lithium ion secondary battery rises, and has a heat resistant temperature of 150. Its function is ensured by inorganic fine particles of ℃ or higher. That is, when the battery becomes hot, even if the porous layer (I) shrinks, the porous layer (II) that does not easily shrink can cause the positive and negative electrodes directly when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact of. Moreover, since this heat-resistant porous layer (II) acts as a skeleton of the separator, the thermal contraction of the porous layer (I), that is, the thermal contraction of the entire separator itself can be suppressed.

  Further, as will be described in detail later, the flat wound electrode body according to the lithium ion secondary battery of the present invention is obtained in a step of being formed into a flat shape by a heating press, and at that time, the separator is mainly porous. Although the thickness of the porous layer (I) is partially reduced, it adheres to the electrode, but in this part of the separator where the thickness is further reduced (corresponding to the part where the current collecting tab of the electrode is disposed) The pores of the separator may be crushed. Where the pores of the separator are crushed, the ion permeability decreases, and this may cause lithium dendrite to deposit on the negative electrode surface, causing an internal short circuit of the battery, but in the lithium ion secondary battery of the present invention, By the action of the porous layer (II) in the separator, the occurrence of an internal short circuit due to such lithium dendrite can be suppressed.

  In the present specification, “the heat resistant temperature is 150 ° C. or higher” in the inorganic fine particles means that no shape change such as deformation is visually confirmed at least at 150 ° C.

  The inorganic fine particles related to the porous layer (II) have a heat-resistant temperature of 150 ° C. or higher, are stable to the non-aqueous electrolyte of the battery, and are electrochemically stable to be hardly oxidized or reduced in the battery operating voltage range. There are no particular restrictions as long as they are appropriate.

Specific examples of such inorganic 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, etc. Nitride fine particles; poorly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; boehmite, zeolite, apatite and kaolin Inorganic fine particles such as mineral-derived substances such as mullite, spinel, olivine, sericite, bentonite, 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. The inorganic fine particles may be used alone or in combination of two or more. Among the inorganic fine particles, silica, alumina, and boehmite are more preferable, and boehmite is particularly preferable.

  The shape of the inorganic fine particles having a heat resistance temperature of 150 ° C. or higher related to the porous layer (II) is not particularly limited, and is substantially spherical (including true sphere), substantially ellipsoid (including ellipsoid), plate-like, etc. Various shapes can be used.

  Further, the average particle size of the inorganic fine particles having a heat resistant temperature of 150 ° C. or higher related to the porous layer (II) is preferably 0.3 μm or more because the ion permeability is lowered if it is too small. More preferably, it is 5 μm or more. In addition, if the inorganic fine particles having a heat resistant temperature of 150 ° C. or higher are too large, the electric characteristics are liable to deteriorate, so the average particle diameter is preferably 5 μm or less, more preferably 2 μm or less.

  In the porous layer (II), since the inorganic fine particles having a heat resistant temperature of 150 ° C. or higher are mainly contained, the total volume of the constituent components of the porous layer (II) of the inorganic fine particles having a heat resistant temperature of 150 ° C. or higher is included. Medium [In the entire volume of all components except the pores. The same applies to the volume content of each component of the porous layer (II). ] Is 50 volume% or more, preferably 70 volume% or more, more preferably 80 volume% or more, and still more preferably 90 volume% or more. By making the content of the inorganic fine particles in the porous layer (II) high as described above, it is possible to satisfactorily suppress the thermal contraction of the entire separator even when the lithium ion secondary battery becomes high temperature. And the occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode can be more effectively suppressed.

  As will be described later, since it is preferable to contain an organic binder in the porous layer (II), the inorganic fine particles having a heat resistant temperature of 150 ° C. or more in the total volume of the constituent components of the porous layer (II) The volume content is preferably 99.5% by volume or less.

  For the porous layer (II), an organic binder is used to bind inorganic fine particles having a heat-resistant temperature of 150 ° C. or more, or to integrate the porous layer (II) and the porous layer (I). It is preferable to contain. Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and fluorine-based binders. Examples include rubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, and epoxy resin. A heat-resistant binder having a heat-resistant temperature is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include “Evaflex Series (EVA)” from Mitsui DuPont Polychemical, EVA from Nihon Unicar, and “Evaflex-EEA Series (Ethylene) from Mitsui DuPont Polychemical. -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  When the organic binder is used for the porous layer (II), it can be used in the form of an emulsion dissolved or dispersed in the solvent for the composition for forming the porous layer (II) described later. Good.

  The volume content of the organic binder in the porous layer (II) is preferably 0.5 to 10% by volume in the total volume of the constituent components of the separator.

  In addition, the porous layer (II) is made of a fibrous material (preferably having a heat-resistant temperature of 150 ° C. or higher), hot-melt resin fine particles (such as PE fine particles), and non-aqueous electrolysis by heating as necessary. Heat-swellable resin fine particles (such as crosslinked polymethyl methacrylate fine particles) that increase the amount of liquid absorption may be contained.

  The separator is, for example, a porous layer (II) -forming composition (slurry, paste, etc.) containing inorganic fine particles having a heat resistant temperature of 150 ° C. or higher, and a microporous film for constituting the porous layer (I). It can be produced by applying to the surface of a sheet-like material such as, and drying to a predetermined temperature to form the porous layer (II).

  The composition for forming the porous layer (II) contains inorganic fine particles having a heat resistant temperature of 150 ° C. or higher, and an organic binder as required, and these are dispersed in a solvent (including a dispersion medium; the same applies hereinafter). It is a thing. The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) may be any solvent as long as it can uniformly disperse inorganic fine particles having a heat-resistant temperature of 150 ° C. or higher, and can uniformly dissolve or disperse the organic binder. Common organic solvents such as aromatic hydrocarbons such as toluene, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. 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 the organic binder 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, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  The composition for forming the porous layer (II) preferably has a solid content containing, for example, inorganic fine particles having an heat resistant temperature of 150 ° C. or higher, an organic binder, and the like, for example, 10 to 80% by mass.

  In the separator, the porous layer (I) and the porous layer (II) do not have to be one each, and a plurality of layers may be present in the separator. For example, it is good also as a structure which has arrange | positioned porous layer (I) on both surfaces of porous layer (II). However, increasing the number of layers may increase the thickness of the separator, leading to an increase in internal resistance of the battery and a decrease in energy density, so it is not preferable to increase the number of layers. The total number of layers of the layer (I) and the porous layer (II) is preferably 5 or less, and particularly preferably 2 layers of the porous layer (I) and the porous layer (II).

  However, in the separator according to the lithium ion secondary battery of the present invention, since the porous layer (I) is attached to the electrode in the flat wound electrode body, at least one of both surfaces of the separator is porous. It consists of a quality layer (I).

  The thickness of the separator is preferably 10 to 30 μm, for example.

  In addition, the thickness of the porous layer (II) [when the separator has a plurality of porous layers (II), the total thickness] is from the viewpoint of more effectively exerting each of the above-described actions by the porous layer (II). It is preferable that it is 3 micrometers or more. However, if the porous layer (II) is too thick, the energy density of the battery may be lowered. Therefore, the thickness of the porous layer (II) is preferably 8 μm or less.

  Furthermore, the thickness of the porous layer (I) [when the separator has a plurality of porous layers (I), the total thickness thereof. same as below. ] Is preferably 6 μm or more, more preferably 10 μm or more, from the viewpoint of more effectively exerting the above-described action (particularly the shutdown action) due to the use of the porous layer (I). However, if the porous layer (I) is too thick, there is a possibility that the energy density of the battery may be lowered. In addition, the force that the porous layer (I) tends to shrink is increased, and the heat of the entire separator is increased. There is a possibility that the action of suppressing the shrinkage becomes small. Therefore, the thickness of the porous layer (I) is preferably 25 μm or less, more preferably 20 μm or less, and further preferably 14 μm or less.

  The porosity of the separator as a whole is preferably 30% or more in a dried state in order to secure a liquid retention amount of the non-aqueous electrolyte and improve ion permeability. On the other hand, from the viewpoint of securing separator strength and preventing internal short circuit, the separator porosity is preferably 70% or less in a dry state. The porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula.

P = {1- (m / t) / (Σa _i · ρ _i )} × 100
Here, in the above formula, a _i : ratio of component i when the total mass is 1, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ), t: thickness of separator (cm).

In the above formula for determining the porosity of the separator, m is the mass per unit area (g / cm ² ) of the porous layer (I), and t is the thickness (cm) of the porous layer (I). and then, by the ratio of component i when set to 1 the entire mass porous layer a _i (I), the porosity of the porous layer (I): can also be determined P (%). The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Further, in the above formula for determining the porosity of the separator, m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness (cm) of the porous layer (II). and then, by the ratio of component i when set to 1 the entire mass porous layer a _i (II), the porosity of the porous layer (II): can also be determined P (%). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

  The lithium ion secondary battery of the present invention has a positive electrode mixture layer containing a positive electrode active material on one or both sides of the current collector, and is collected on the exposed portion of the current collector where the positive electrode mixture layer is not formed. A positive electrode having a current tab and a negative electrode mixture layer containing a negative electrode active material on one or both sides of the current collector, and the current collector tab is disposed on an exposed portion of the current collector where the negative electrode mixture layer is not formed A step (1) of forming a wound electrode body by winding a laminate in which a separator is disposed between a positive electrode and a negative electrode using a negative electrode having the negative electrode and the separator; and A step of forming a flat wound electrode body through a step (2) of applying a hot press to flatten the cross section and attaching the separator porous layer (I) to the positive electrode and / or the negative electrode (2). It can be manufactured by the method of the present invention.

  In the step (2), the heating press is performed under conditions of a temperature of 40 to 70 ° C. and a pressure of 1.96 to 9.80 MPa. Thereby, a flat wound electrode body in which the X in the separator is 80% or more and 95% or less can be formed while the porous layer (I) of the separator is attached to the electrode. The time for the heating press in the step (2) is preferably 0.5 to 10 seconds, for example.

  The positive electrode and the negative electrode used for the flat wound electrode body have current collecting tabs. Usually, when the wound electrode body is heated and pressed flatly in the step (2), Since the press stress is the largest at the location, the portion corresponding to the portion of the separator is most deformed and becomes thinner than the other portions. In the method of the present invention, by controlling the heating press conditions in step (2) as described above, the thickness of the separator is 80% to 95% of the thickest part (that is, the X Is adjusted to be 80% or more and 95% or less), and the lithium ion secondary battery of the present invention can be manufactured.

  In addition, as described above, in the heating press, the heating temperature at that time is relatively low and the constituent components of the separator and the positive and negative electrodes are difficult to melt. It is considered that a lithium ion secondary battery capable of suppressing variation in thickness immediately after manufacture can be manufactured based on this, due to some physical action accompanying deformation of the porous layer (I). ing.

  That is, in the flat wound electrode body, the porous layer (I) of the separator is attached to the electrode, and the value of X in the separator is 95% or less, so that a large number of lithium ion secondary particles can be obtained. When the secondary battery is manufactured, variations in thickness can be suppressed. The value of X in the separator is more preferably 90% or less.

  In addition, even though the pores of the separator may be partially crushed by the above-mentioned hot press, it is possible to suppress clogging of the pores due to melting of the constituent materials of the separator, so the separator in the flat wound electrode body The overall ion permeability can be kept high. Therefore, the lithium ion secondary battery of the present invention having such a flat wound electrode body can suppress the deterioration of the battery characteristics accompanying the blockage of the pores of the separator, for example, excellent load characteristics Can be secured.

  However, in the flat wound electrode body, if the value of X in the separator becomes too small (that is, if the degree of deformation of the separator is too large), the ion permeability of the separator is too low, or the lithium ion secondary The load characteristics of the battery will deteriorate. In the flat wound electrode body, the value of X in the separator is 80% or more. The value of X in the separator is more preferably 85% or more.

  In the lithium ion secondary battery of the present invention, it is preferable that the porous layer (I) of the separator is attached to at least the negative electrode. Normally, the volume change due to pre-charging during battery manufacture is larger for the negative electrode than for the positive electrode, and when the negative electrode is attached to the separator porous layer (I), the variation in battery thickness is better. Can be suppressed.

  Therefore, in the step (1) in the method of the present invention, when laminating the positive electrode, the negative electrode, and the separator, it is more preferable to laminate so that at least the porous layer (I) of the separator faces the negative electrode.

  In the lithium ion secondary battery of the present invention, for example, the separator may be attached to both the positive electrode and the negative electrode. In this case, both the positive electrode and the negative electrode are attached to the porous layer (I) of the separator. Therefore, a separator having both surfaces of the porous layer (I) is used.

  In the production of a lithium ion secondary battery, the processes other than the formation of the flat wound electrode body are the same as the various processes employed in the production of a conventionally known lithium ion secondary battery. Can do. For example, the flat spirally wound electrode body is accommodated in the exterior body, and the external terminals of the battery and the positive and negative current collecting tabs of the flat spirally wound electrode body are electrically connected according to a conventional method, and non-aqueous electrolysis is performed. After injecting the liquid into the exterior body, a lithium ion secondary battery can be obtained through preliminary charging (chemical conversion treatment) performed before or after sealing the exterior body and sealing of the exterior body.

  In the negative electrode according to the lithium ion secondary battery of the present invention, a negative electrode active material and a binder, and further, a negative electrode mixture layer comprising a negative electrode mixture containing a conductive auxiliary agent as necessary, are provided on one or both sides of the current collector. A structure having the following structure is used.

  Examples of the negative electrode active material include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and metals that can be alloyed with lithium (Si , Sn, etc.) or alloys thereof, oxides, etc., and one or more of these can be used.

Among the negative electrode active materials, in order to increase the capacity of the battery, in particular, a material containing Si and O as constituent elements (provided that the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5 Hereinafter, the material is preferably referred to as “SiO _x ”.

In addition, since a high capacity negative electrode active material such as SiO _x has a large volume change amount due to charging / discharging of the battery, in the case of using a negative electrode containing the same, a flat shape is used in precharging at the time of battery manufacture. There is a possibility that the wound electrode body is expanded and the variation in battery thickness is further increased. However, in the lithium ion secondary battery of the present invention, in the flat wound electrode body, the porous layer (I) of the separator and the electrode are attached, and the value of X in the separator is controlled, Thereby, even when a high-capacity negative electrode active material such as SiO _x is used, variation in thickness immediately after the battery is manufactured can be suppressed.

In addition, by using a high-capacity negative electrode active material, the safety required for the lithium ion secondary battery (especially safety under abnormally high temperatures) becomes higher, but the lithium ion secondary of the present invention As described above, the battery has a separator having a porous layer (I) capable of ensuring shutdown characteristics and a porous layer (II) excellent in heat resistance, and has a structure in which the separator and the electrode are attached. Since the flat wound electrode body is provided, even if a high-capacity negative electrode active material such as SiO _x is used, extremely excellent safety can be obtained.

The SiO _x may contain Si microcrystal or amorphous phase. In this case, the atomic ratio of Si and O is a ratio including Si microcrystal or amorphous phase Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is sufficient that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 in combination with Si. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the material has a molar ratio of SiO ₂ to Si of 1: 1, x = 1, so that the structural formula is represented by SiO. The In the case of a material having such a structure, for example, in X-ray diffraction analysis, a peak due to the presence of Si (microcrystalline Si) may not be observed, but when observed with a transmission electron microscope, the presence of fine Si Can be confirmed.

Then, SiO _x is preferably a complex complexed with carbon materials, for example, it is desirable that the surface of the SiO _x is coated with a carbon material. As described above, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of securing good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is used. It is necessary to form an excellent conductive network by mixing and dispersing the material and the conductive material well. If complexes complexed with carbon material SiO _x, for example, simply than with a material obtained by mixing a conductive material such as SiO _x and the carbon material, good conductive network in the negative electrode Formed.

The complex of the SiO _x and the carbon material, as described above, other although the surface of the SiO _x coated with carbon material, such as granules of SiO _x and the carbon material can be cited.

In addition, since the composite in which the surface of SiO _x is coated with a carbon material is further combined with a conductive material (carbon material or the like), a better conductive network can be formed in the negative electrode. Therefore, it is possible to realize a lithium ion secondary battery with higher capacity and more excellent battery characteristics (for example, charge / discharge cycle characteristics). The complex of the SiO _x and the carbon material coated with a carbon material, for example, like granules the mixture was further granulated with SiO _x and the carbon material coated with a carbon material.

Further, as SiO _x whose surface is coated with a carbon material, the surface of a composite (for example, a granulated body) of SiO _x and a carbon material having a smaller specific resistance value is further coated with a carbon material. Those can also be preferably used. In a state where SiO _x and the carbon material are dispersed in the granulated body, a better conductive network can be formed. Therefore, in a lithium ion secondary battery having a negative electrode containing SiO _x as a negative electrode active material, Battery characteristics such as load discharge characteristics can be further improved.

Preferred examples of the carbon material that can be used to form a composite with SiO _x include carbon materials such as low crystalline carbon, carbon nanotubes, and vapor grown carbon fibers.

The details of the carbon material include at least one selected from the group consisting of fibrous or coiled carbon materials, carbon black (including acetylene black and ketjen black), artificial graphite, graphitizable carbon, and non-graphitizable carbon. A seed material is preferred. Fibrous or coil-like carbon materials are preferable in that they easily form a conductive network and have a large surface area. Carbon black (including acetylene black and ketjen black), graphitizable carbon, and non-graphitizable carbon have high electrical conductivity and high liquid retention, and even if SiO _x particles expand and contract. This is preferable in that it has a property of easily maintaining contact with the particles.

Further, as will be described in detail later, in the present invention, graphite is preferably used as a negative electrode active material together with SiO _x , but this graphite is used as a carbon material related to a composite of SiO _x and a carbon material. You can also. Graphite, like carbon black, has high electrical conductivity and high liquid retention, and also has the property of easily maintaining contact with the SiO _x particles even when they expand and contract. Therefore, it can be preferably used for forming a complex with SiO _x .

Among the carbon materials exemplified above, a fibrous carbon material is particularly preferable for use when the composite with SiO _x is a granulated body. Fibrous carbon material can follow the expansion and contraction of SiO _x with the charging and discharging of the battery due to the high shape is thin threadlike flexibility, also because bulk density is large, many and SiO _x particles It is because it can have a junction. Examples of the fibrous carbon include polyacrylonitrile (PAN) -based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and carbon nanotube, and any of these may be used.

The fibrous carbon material can also be formed on the surface of the SiO _x particles by, for example, a vapor phase method.

The specific resistance value of SiO _x is usually 10 ³ to 10 ⁷ kΩcm, while the specific resistance value of the carbon material exemplified above is usually 10 ^{−5 to} 10 kΩcm.

The composite of SiO _x and the carbon material may further have a material layer (a material layer containing non-graphitizable carbon) that covers the carbon material coating layer on the particle surface.

When a composite of SiO _x and a carbon material is used for the negative electrode, the ratio of SiO _x and the carbon material is based on SiO _x : 100 parts by mass from the viewpoint of satisfactorily exerting the effect of the composite with the carbon material. The carbon material is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. Further, in the composite, if the ratio of the carbon material to be combined with SiO _x is too large, it may lead to a decrease in the amount of SiO _x in the negative electrode mixture layer, and the effect of increasing the capacity may be reduced. SiO _x: relative to 100 parts by weight, the carbon material, and more preferably preferably not more than 50 parts by weight, more than 40 parts by weight.

The composite of the SiO _x and the carbon material can be obtained, for example, by the following method.

First, a manufacturing method in the case of combining SiO _x will be described. A dispersion liquid in which SiO _x is dispersed in a dispersion medium is prepared, and sprayed and dried to produce composite particles including a plurality of particles. For example, ethanol or the like can be used as the dispersion medium. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. In addition to the above method, similar composite particles can be produced also by a granulation method by a mechanical method using a vibration type or planetary type ball mill or rod mill.

Incidentally, the SiO _x, in the case of manufacturing a granulated body with small carbon material resistivity value than SiO _x is adding the carbon material in the dispersion liquid of SiO _x are dispersed in a dispersion medium, the dispersion by using a liquid, by a similar method to the case of composite of SiO _x may be a composite particle (granule). Further, by granulation process according to the similar mechanical method, it is possible to produce a granular material of the SiO _x and the carbon material.

Next, when the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is coated with a carbon material to form a composite, for example, the SiO _x particles and the hydrocarbon-based material The gas is heated in the gas phase, and carbon generated by pyrolysis of the hydrocarbon-based gas is deposited on the surface of the particles. As described above, according to the vapor deposition (CVD) method, the hydrocarbon-based gas spreads to every corner of the composite particle, and the surface of the particle and the pores in the surface are thin and contain a conductive carbon material. Since a uniform film (carbon material coating layer) can be formed, the SiO _x particles can be imparted with good conductivity with a small amount of carbon material.

In the production of SiO _x coated with a carbon material, the processing temperature (atmosphere temperature) of the vapor deposition (CVD) method varies depending on the type of hydrocarbon gas, but usually 600 to 1200 ° C. is appropriate. Among these, the temperature is preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the treatment temperature, the less the remaining impurities, and the formation of a coating layer containing carbon having high conductivity.

  As the liquid source of the hydrocarbon-based gas, toluene, benzene, xylene, mesitylene and the like can be used, but toluene that is easy to handle is particularly preferable. A hydrocarbon-based gas can be obtained by vaporizing them (for example, bubbling with nitrogen gas). Moreover, methane gas, acetylene gas, etc. can also be used.

In addition, after the surface of SiO _x particles (SiO _x composite particles or a granulated body of SiO _x and a carbon material) is covered with a carbon material by a vapor deposition (CVD) method, a petroleum-based pitch or a coal-based pitch is used. At least one organic compound selected from the group consisting of a thermosetting resin and a condensate of naphthalene sulfonate and aldehydes is attached to a coating layer containing a carbon material, and then the organic compound is attached. The obtained particles may be fired.

Specifically, a dispersion liquid in which a SiO _x particle (SiO _x composite particle or a granulated body of SiO _x and a carbon material) coated with a carbon material and the organic compound are dispersed in a dispersion medium is prepared, The dispersion is sprayed and dried to form particles coated with the organic compound, and the particles coated with the organic compound are fired.

  An isotropic pitch can be used as the pitch, and a phenol resin, a furan resin, a furfural resin, or the like can be used as the thermosetting resin. As the condensate of naphthalene sulfonate and aldehydes, naphthalene sulfonic acid formaldehyde condensate can be used.

As a dispersion medium for dispersing the SiO _x particles coated with the carbon material and the organic compound, for example, water or alcohols (ethanol or the like) can be used. It is appropriate to spray the dispersion in an atmosphere of 50 to 300 ° C. The firing temperature is usually 600 to 1200 ° C., preferably 700 ° C. or higher, and more preferably 800 ° C. or higher. This is because the higher the processing temperature, the less the remaining impurities, and the formation of a coating layer containing a high-quality carbon material with high conductivity. However, the processing temperature needs to be lower than the melting point of SiO _x .

When using SiO _x for the negative electrode active material according to the lithium ion secondary battery of the present invention, it is preferable to use graphite as the negative electrode active material. By reducing the ratio of SiO _x in the negative electrode active material using graphite, the negative electrode (negative electrode mixture) associated with charging / discharging of the battery is suppressed as much as possible while suppressing the decrease in the capacity-enhancing effect due to the reduction of SiO _x. It is possible to suppress a change in volume of the layer) and to suppress a decrease in battery characteristics that may be caused by the volume change.

Examples of graphite used as the negative electrode active material together with SiO _x include natural graphite such as flaky graphite; graphitizable carbon such as pyrolytic carbons, mesophase carbon microbeads (MCMB), and carbon fibers at 2800 ° C. or more. Artificial graphite subjected to chemical treatment; and the like.

In the negative electrode according to the present invention, from the viewpoint of satisfactorily ensuring the effect of the high capacity by using a SiO _x, the content of SiO _x in the anode active material is 0.01 wt% or more It is preferably 3% by mass or more. Further, from the viewpoint of better avoiding the problem due to the volume change of the negative electrode due to charge / discharge, the content of SiO _x in the negative electrode active material is preferably 30% by mass or less, and 20% by mass or less. Is more preferable.

  Examples of the binder related to the negative electrode mixture layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like. Further, when the conductive additive is included in the negative electrode mixture layer, examples of the conductive assistant include natural graphite (such as flake graphite) and graphite such as artificial graphite (graphitic carbon material); acetylene black, ketjen Carbon materials such as carbon black such as black, channel black, furnace black, lamp black and thermal black; carbon fiber;

  The negative electrode is, for example, in the form of a paste or slurry in which a negative electrode active material and a binder, and further a conductive assistant used as necessary are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) or water. A step of preparing a negative electrode mixture-containing composition (however, the binder may be dissolved in a solvent), applying this to one or both sides of the current collector, drying, and applying a calender treatment as necessary It is manufactured through.

  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 5 μm in order to ensure mechanical strength. Is desirable.

  Moreover, the current collection tab for electrically connecting with the other member in a lithium ion secondary battery is attached to a negative electrode. For example, an exposed portion that does not form the negative electrode mixture layer is left on at least a part of the current collector of the negative electrode, and a nickel foil, a copper foil, or the like serving as a current collecting tab can be welded and attached thereto. Although there is no restriction | limiting in particular in the attachment position of a current collection tab, Usually, it is set to the vicinity of either of the both ends of a negative electrode (strip | belt-shaped negative electrode). The thickness of the current collecting tab is preferably 10 to 100 μm, for example.

  The negative electrode according to the lithium ion secondary battery of the present invention is not limited to the one manufactured by the above manufacturing method, and may be one manufactured by another method.

  The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per one surface of the current collector, for example. Moreover, as a composition of a negative mix layer, it is preferable that a negative electrode active material shall be 80.0-99.8 mass% and a binder shall be 0.1-10 mass%, for example. Furthermore, when making a negative mix layer contain a conductive support agent, it is preferable that the quantity of the conductive support agent in a negative mix layer shall be 0.1-10 mass%.

  As the positive electrode according to the lithium ion secondary battery of the present invention, one having a structure having a positive electrode mixture layer containing a positive electrode active material, a binder, a conductive additive and the like on one side or both sides of a current collector is used.

Examples of the positive electrode active material include lithium cobalt oxide; lithium manganese oxide such as LiMnO ₂ and Li ₂ MnO ₃ ; lithium nickel oxide such as LiNiO ₂ ; lithium-containing composite oxide having a layered structure such as LiCo _1-x NiO ₂ A lithium-containing composite oxide having a spinel structure such as LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ ; a lithium-containing composite oxide having an olivine structure such as LiFePO ₄ ; Or an oxide substituted with can be used.

  Among these lithium-containing composite oxides, since the capacity is larger, it is more preferable to use lithium-containing composite oxide (A) (lithium nickel cobalt manganese oxide) represented by the following general composition formula (1). preferable.

Li _{1 + a} Ni _1-bc-d Co _b Mn _c M ¹ _d O ₂ (1)

In the general composition formula (1), M ¹ is selected from the group consisting of Mg, Al, Ti, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Sn, W, B, P, and Bi. At least one element, −0.15 ≦ a ≦ 0.15, 0.05 ≦ b ≦ 0.4, 0.05 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.03, and b + c + d ≦ 0.7.

  The positive electrode active material having a high capacity such as the lithium-containing composite oxide (A) represented by the general composition formula (1) has a large volume change amount due to charging / discharging of the battery. When the battery is used, there is a possibility that the flat wound electrode body is expanded in the preliminary charging at the time of manufacturing the battery, and the variation in the battery thickness is further increased. However, in the lithium ion secondary battery of the present invention, in the flat wound electrode body, the porous layer (I) of the separator and the electrode are attached, and the value of X in the separator is controlled, Thus, even when a high-capacity positive electrode active material such as the lithium-containing composite oxide (A) represented by the general composition formula (1) is used, variation in thickness immediately after battery manufacture can be suppressed. .

  In addition, by using a high-capacity positive electrode active material, the safety required for lithium ion secondary batteries (especially safety under abnormally high temperatures) becomes higher, but the lithium ion secondary of the present invention As described above, the battery has a separator having a porous layer (I) capable of ensuring shutdown characteristics and a porous layer (II) excellent in heat resistance, and has a structure in which the separator and the electrode are attached. Since it has a flat wound electrode body, it is very excellent even when a high-capacity positive electrode active material such as the lithium-containing composite oxide (A) represented by the general composition formula (1) is used. It can have safety.

  The positive electrode active material includes a lithium-containing composite oxide (A) represented by the general composition formula (1) and a lithium-containing composite oxide (B) (lithium represented by the following general composition formula (2). It is more preferable to use (cobalt oxide) in combination.

_{Li 1 + o Co 1-p} -q Mg p M 2 q O 2 (2)

In the general composition formula (2), M ² is at least one selected from the group consisting of Al, Ti, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Sn, W, B, P, and Bi. It is a seed element, with −0.3 ≦ o ≦ 0.3, 0 ≦ p ≦ 0.1, and 0 ≦ q ≦ 0.1. In the general composition formula (2), 0.001 ≦ p ≦ 0.1 is more preferable, and 0 <q ≦ 0.1 is more preferable.

  When the lithium-containing composite oxide (A) and the lithium-containing composite oxide (B) are used in combination with the positive electrode active material, the lithium-containing composite oxide (A) in 100% by mass of these in total The content is preferably 10 to 50% by mass.

  As the binder related to the positive electrode mixture layer, the same ones exemplified above as the binder related to the negative electrode mixture layer can be used. Moreover, the same thing as what was illustrated previously as a conductive support agent which concerns on a negative mix layer can be used for the conductive support agent which concerns on a positive mix layer.

  For the positive electrode, for example, a paste-like or slurry-like positive electrode mixture-containing composition in which a positive electrode active material, a binder, a conductive auxiliary agent, and the like are dispersed in a solvent such as NMP is prepared (however, the binder is dissolved in the solvent). It may be manufactured through a step of applying a calender treatment as necessary after applying it to one or both sides of the current collector and drying it.

  As the current collector for the positive electrode, the same one as used for the positive electrode of a conventionally known lithium ion secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  Moreover, the current collection tab for electrically connecting with the other member in a lithium ion secondary battery is attached to a positive electrode. For example, at least a part of the current collector of the positive electrode is left with an exposed portion where the positive electrode mixture layer is not formed, and an aluminum foil, a nickel foil, or the like serving as a current collecting tab can be welded thereto. Although there is no restriction | limiting in particular in the attachment position of a current collection tab, Usually, it is set as the vicinity of either of the both ends of a positive electrode (band-shaped positive electrode). The thickness of the current collecting tab is preferably 10 to 100 μm, for example.

  The positive electrode according to the lithium ion secondary battery of the present invention is not limited to that manufactured by the above manufacturing method, and may be manufactured by other methods.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 60-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass.

As the nonaqueous electrolytic solution according to the lithium ion secondary battery of the present invention, 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 (R _f OSO ₂ ) ₂ [where Rf is a fluoroalkyl group], or the like is used. Can do.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, 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 dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme, cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran, nitriles such as acetonitrile, propionitrile and methoxypropionitrile And sulfites such as ethylene glycol sulfite. These may be used as a mixture of two or more. Kill. 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.

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

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, and fluorobenzene are used for the purpose of improving safety, charge / discharge cycle characteristics, and high-temperature storage characteristics of these non-aqueous electrolytes. Additives such as halogen-substituted cyclic carbonates such as t-butylbenzene, 4-fluoro-1,3-dioxolan-2-one (FEC), and phosphonoacetates such as ethyl diethylphosphonoacetate (EDPA) It can also be added.

  Furthermore, as the non-aqueous electrolyte of the lithium ion secondary battery, a gel (gel electrolyte) obtained by adding a known gelling agent such as a polymer to the non-aqueous electrolyte may be used.

  Examples of the form of the lithium ion secondary battery of the present invention 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 lithium ion secondary battery of this invention can be used for the same use as the various uses to which the conventionally known lithium ion secondary battery is applied.

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

Example 1
<Preparation of separator>
5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) are added to 5 kg of boehmite secondary aggregates having an average particle size of 3 μm. A dispersion was prepared by crushing for 10 hours with a ball mill at 40 times / min. When a part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM), the shape of boehmite was almost plate-like. The average particle size of the boehmite after the treatment was 1 μm.

  To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added and stirred with a three-one motor for 3 hours to form a uniform slurry. [Slurry for forming porous layer (II), solid content ratio: 50% by mass] was prepared.

PE microporous separator for a lithium ion secondary battery (porous layer (I): thickness 12 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.) corona discharge treatment (discharge amount) 40 W · min / m ² ), and a slurry for forming a porous layer (II) is applied to the treated surface by a micro gravure coater and dried to form a porous layer (II) having a thickness of 4 μm. Got. The mass per unit area of the porous layer (II) in this separator was 5.5 g / m ² , the boehmite volume content was 95% by volume, and the porosity was 45%.

<Preparation of positive electrode>
LiCoO ₂ [lithium-containing composite oxide (B)] and Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O ₂ [lithium-containing composite oxide (A)] in a ratio of 80:20 (mass 100 parts by weight of the positive electrode active material mixed in a ratio), 20 parts by weight of an NMP solution containing PVDF as a binder at a concentration of 10% by weight, 1 part by weight of artificial graphite and 1 part by weight of ketjen black as a conductive aid, Was kneaded using a biaxial kneader, and NMP was further added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

  After coating the positive electrode mixture-containing paste on both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a positive electrode mixture layer on both surfaces of the aluminum foil. did. Thereafter, press treatment is performed to adjust the thickness and density of the positive electrode mixture layer, and nickel foil (exposed portion of the positive electrode mixture layer) is provided in the vicinity of one end of one surface of the current collector. A current collecting tab having a thickness of 80 μm was welded to produce a strip-like positive electrode having a length of 375 mm and a width of 43 mm. The positive electrode mixture layer in the obtained positive electrode had a thickness of 55 μm per one side.

<Production of negative electrode>
A composite in which the surface of SiO having an average particle diameter D _50% of 8 μm, which is a negative electrode active material, is coated with a carbon material (the amount of the carbon material in the composite is 10 mass%, hereinafter referred to as “SiO / carbon composite”). And graphite having an average particle diameter D _50% of 16 μm mixed with an amount of SiO / carbon composite of 5% by mass: 97.5 parts by mass, and SBR as a binder: 1.5 Water was added to and mixed with parts by mass and CMC as a thickener: 1 part by mass to prepare a negative electrode mixture-containing paste.

  After applying the negative electrode mixture-containing paste to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, vacuum drying is performed at 120 ° C. for 12 hours to form a negative electrode mixture layer on both sides of the copper foil. did. Thereafter, press treatment is performed to adjust the thickness and density of the negative electrode mixture layer, and nickel foil (exposed portion of the negative electrode mixture layer) is provided in the vicinity of one end of one surface of the current collector. A current collecting tab having a thickness of 80 μm was welded to produce a strip-shaped negative electrode having a length of 380 mm and a width of 44 mm. The negative electrode mixture layer in the obtained negative electrode had a thickness of 65 μm per one surface.

<Formation of flat wound electrode body>
The separator was disposed between the positive electrode and the negative electrode, laminated, and wound into a spiral shape to obtain a wound electrode body. Note that the porous layer (I) of the separator was opposed to the negative electrode during the above lamination. Thereafter, the wound electrode body was heated and pressed at a temperature of 60 ° C. and a pressure of 4.5 MPa for 5.0 seconds to obtain a flat wound electrode body. In this way, when a plurality of flat wound electrode bodies were formed and part of them were disassembled, the separator [the porous layer (I)] and the negative electrode were adhered, and the thickness of the separator was further examined. However, the thickness a of the thinnest part was 13.1 μm, the thickness b of the thickest part was 16 μm, and the value of X was 82%.

<Battery assembly>
The flat wound electrode body is inserted into an aluminum alloy prismatic battery case having outer thickness of 4.0 mm, width of 34 mm, and height of 50 mm. While welding, an aluminum alloy lid plate was welded to the open end of the battery case. Thereafter, LiPF ₆ was added to a concentration of 1.1 mol / l in a non-aqueous electrolyte (a solvent in which ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a volume ratio = 1: 1: 1) from an inlet provided on the cover plate. The solution was added to the solution so that FEC was added in an amount of 2.0% by mass and VC was added in an amount of 1.0% by mass. After the inlet was sealed, a chemical conversion treatment by precharging was performed to obtain a lithium ion secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG.

  Here, the battery shown in FIGS. 1 and 2 will be described. FIG. 1A is a plan view, and FIG. 1B is a partial cross-sectional view thereof. As shown in FIG. 2 and the separator 3 are accommodated in a rectangular (square tube) battery case 4 as a flat wound electrode body 6 together with a non-aqueous electrolyte. However, in FIG. 1, in order to avoid complication, a metal foil, a non-aqueous electrolyte, or the like as a current collector used for manufacturing the positive electrode 1 and the negative electrode 2 is not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The battery case 4 also serves as a positive electrode terminal. And the insulator 5 which consists of PE sheets is arrange | positioned at the bottom part of the battery case 4, and it connects to each one end of the positive electrode 1 and the negative electrode 2 from the flat wound electrode body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3. The positive electrode current collecting tab 7 and the negative electrode current collecting tab 8 are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached.

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIG. 1, a non-aqueous electrolyte inlet 14 is provided in the cover plate 9, and a sealing member is inserted into the non-aqueous electrolyte inlet 14, for example, laser welding or the like. (See FIG. 1 and FIG. 2, in practice, the non-aqueous electrolyte inlet 14 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 14). Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Example 1, the outer can 5 and the lid plate 9 function as positive terminals by directly welding the positive electrode current collecting tab 7 to the lid plate 9, and the negative electrode current collecting tab 8 is welded to the lead plate 13. The negative electrode current collecting tab 8 and the terminal 11 are electrically connected to each other through the lead plate 13 so that the terminal 11 functions as a negative electrode terminal. However, depending on the material of the battery case 4, the polarity may be reversed. Sometimes it becomes.

  FIG. 2 is a perspective view schematically showing the external appearance of the battery shown in FIG. 1. FIG. 2 is shown for the purpose of showing that the battery is a square battery. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 1, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
A flat wound electrode body was formed in the same manner as in Example 1 except that the heating press conditions were changed to a temperature of 60 ° C., a pressure of 3.0 MPa, and a time of 5.0 seconds. A lithium ion secondary battery was produced in the same manner as in Example 1 except that it was used.

  When a part of the formed flat wound electrode body was disassembled, the separator [its porous layer (I)] and the negative electrode were adhered, and when the thickness of the separator was further examined, the thickness of the thinnest part a was 13.6 μm, the thickness b of the thickest part was 16 μm, and the value of X was 85%.

Example 3
A flat wound electrode body was formed in the same manner as in Example 1 except that the heating press conditions were changed to a temperature of 60 ° C., a pressure of 2.3 MPa, and a time of 5.0 seconds. A lithium ion secondary battery was produced in the same manner as in Example 1 except that it was used.

  When a part of the formed flat wound electrode body was disassembled, the separator [its porous layer (I)] and the negative electrode were adhered, and when the thickness of the separator was further examined, the thickness of the thinnest part a was 14.9 μm, the thickness b of the thickest part was 16 μm, and the value of X was 93%.

Example 4
A positive electrode was produced in the same manner as in Example 1 except that only the positive electrode active material was changed to LiCoO ₂ , and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 5
Example 1 except that the positive electrode active material was changed to a mixture containing LiCoO ₂ and Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O ₂ in a ratio (mass ratio) of 90:10. A positive electrode was produced in the same manner, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 6
Example 1 except that the positive electrode active material was changed to a mixture containing LiCoO ₂ and Li _1.0 Ni _0.8 Co _0.1 Mn _0.1 O ₂ in a ratio (mass ratio) of 70:30. A positive electrode was produced in the same manner, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 7
A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was changed to only graphite, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Example 8
As the negative electrode active material, the same SiO / carbon composite as that used in Example 1 and graphite having an average particle diameter D _50% of 16 μm were added in such an amount that the amount of the SiO / carbon composite was 10% by mass. A negative electrode was produced in the same manner as in Example 1 except that the mixture was changed to a mixed mixture, and a lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode was used.

Example 9
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode active material was changed to LiCoO ₂ only. A negative electrode was produced in the same manner as in Example 1 except that the negative electrode active material was changed to only graphite. And the lithium ion secondary battery was produced like Example 1 except having used these positive electrodes and negative electrodes.

Comparative Example 1
A flat wound electrode body was formed in the same manner as in Example 1 except that the heating press conditions were changed to a temperature of 80 ° C., a pressure of 9.0 MPa, and a time of 10 seconds, and this flat wound electrode body was used. A lithium ion secondary battery was produced in the same manner as in Example 1 except for the above.

  When a part of the formed flat wound electrode body was disassembled, the separator [its porous layer (I)] and the negative electrode were adhered, and when the thickness of the separator was further examined, the thickness of the thinnest part a was 12.0 μm, the thickness b of the thickest part was 16 μm, and the value of X was 75%.

Comparative Example 2
A flat wound electrode body was formed in the same manner as in Example 1 except that the heating press conditions were changed to a temperature of 40 ° C., a pressure of 1.0 MPa, and a time of 5.0 seconds. A lithium ion secondary battery was produced in the same manner as in Example 1 except that it was used.

  When a part of the formed flat wound electrode body was disassembled, the separator [its porous layer (I)] and the negative electrode were not adhered very well, and when the thickness of the separator was further investigated, The thickness a of the thinnest part was 15.7 μm, the thickness b of the thickest part was 16 μm, and the value of X was 98%.

Comparative Example 3
A flat wound electrode body was formed in the same manner as in Example 1 except that the spirally wound electrode body was inserted into the battery case as it was without performing a heating press. This flat wound electrode body A lithium ion secondary battery was produced in the same manner as in Example 1 except that was used.

  When a part of the formed flat wound electrode body was disassembled, the separator [its porous layer (I)] and the negative electrode were not adhered, and when the thickness of the separator was further examined, the separator was deformed. It was not recognized, and the thickness corresponding to the location where the current collecting tabs of the positive electrode and the negative electrode were located was 16 μm.

Comparative Example 4
In Example 1, the PE microporous separator for a lithium ion secondary battery used for the porous layer (I) of the separator was used as it was without forming the porous layer (II). A lithium ion secondary battery was produced in the same manner as in Example 1.

  In addition, when the flat wound electrode body formed by the same method as that used for the lithium ion secondary battery of Comparative Example 4 was disassembled, the separator and the negative electrode were adhered, and the thickness of the separator was further examined. The thickness a of the thinnest part was 10.2 μm, the thickness b of the thickest part was 12 μm, and the value of X was 85%.

Comparative Example 5
A flat wound electrode body was formed in the same manner as in Example 1 except that the heating press conditions were changed to a temperature of 80 ° C., a pressure of 0.5 Pa, and a time of 60.0 seconds. A lithium ion secondary battery was produced in the same manner as in Example 1 except that it was used.

  When a part of the formed flat wound electrode body was disassembled, the separator [its porous layer (I)] and the negative electrode were not adhered very well, and when the thickness of the separator was further investigated, The thickness a of the thinnest part was 15.8 μm, the thickness b of the thickest part was 16 μm, and the value of X was 99%.

  Table 1 shows the configurations of the lithium ion secondary batteries of Examples and Comparative Examples. In Table 1, for convenience, the value of X in the separator according to Comparative Example 3 is expressed as 100%.

  Moreover, each evaluation below was performed about each lithium ion secondary battery of an Example and a comparative example. These results are shown in Table 2.

<Evaluation of thickness variation>
For each of the 100 batteries of the examples and comparative examples, the thickness was measured at the same location immediately after assembly (immediately after sealing through chemical conversion treatment by precharging). Then, the degree of thickness variation was evaluated according to the following criteria for each example and comparative example.
○: The standard deviation σ is in the range of 0.03 mm or less.
X: The distribution of the standard deviation σ is greater than 0.03 mm.

<Initial capacity measurement>
About each battery of an Example and a comparative example, constant current charge was performed until the voltage became 4.35V with the electric current value of 0.5C, and it charged with the constant voltage of 4.35V after that. The termination current at this time was 0.05C. Subsequently, each battery after charging was discharged at a current value of 0.2 C until the voltage reached 2.75 V, and the capacity (initial capacity) at that time was measured. In Table 2, the initial capacity of each battery is shown as a relative value when the capacity of the battery of Example 1 is 100.

<Evaluation of load characteristics>
About each battery of an Example and a comparative example, constant current charge and constant voltage charge were performed on the same conditions as the time of initial capacity measurement after the above-mentioned initial capacity measurement. Subsequently, each battery after charging was discharged at a current value of 1 C until the voltage reached 2.75 V, and the capacity at that time (1 C capacity) was measured. And about each battery, the value which remove | divided 1C capacity | capacitance by the initial stage capacity was represented by the percentage, and the capacity | capacitance maintenance factor was calculated | required. The higher the capacity retention rate, the better the load characteristics of the battery.

<150 ° C heating test>
About each battery of an Example and a comparative example, it charged on the same conditions as the time of initial stage capacity | capacitance measurement. Each battery after charging is placed in a thermostatic bath, heated from 30 ° C. to 150 ° C. at a rate of 5 ° C./minute, then held at 150 ° C. for 6 hours, and the surface of the battery in the meantime using a thermocouple The temperature was measured. A battery having a surface temperature of 160 ° C. or lower was evaluated as “◯ (good safety)”, and a battery having a surface temperature exceeding 160 ° C. (a battery that caused thermal runaway) was evaluated as “× (safety is It was inferior) ”.

  As shown in Table 2, the lithium ion secondary of Examples 1 to 9 in which the porous layer (I) of the separator and the electrode are adhered in the flat wound electrode body and the value of X in the separator is appropriate. In the battery, variation in thickness immediately after production is suppressed, and the safety evaluated in the 150 ° C. heating test is superior to the battery of Comparative Example 4 using a normal microporous membrane separator, Load characteristics are also good.

  On the other hand, the battery of Comparative Example 1 in which the value of X in the separator is too small has poor load characteristics. Further, the batteries of Comparative Examples 2, 3, and 5 in which the value of X in the separator is too large have a large thickness variation immediately after manufacture, and are inferior in safety as evaluated by a 150 ° C. heating test.

  In addition, about the lithium ion secondary battery of Example 1, the end voltage at the time of constant current charge and the conditions at the time of constant voltage charge were changed to 4.20V, 4.30V, 4.40V, and 4.45V, The initial capacity measurement, load characteristic evaluation, and 120 ° C. heating test were carried out in the same manner as above. These results are shown in Table 3. In Table 3, the case where the voltage condition is set to 4.20V is set to Example 1a, 4.30V is set to Example 1b, 4.40V is set to Example 1c, and 4.45V is set. Example 1d is adopted. Table 3 also shows the evaluation results of the lithium ion secondary battery of Example 1 in which the voltage condition is 4.35V.

  As shown in Table 3, while the lithium ion secondary battery of Example 1 can improve the initial capacity by increasing the end voltage during charging, safety and load can be improved even under such charging conditions. Good characteristics.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 6 Flat wound electrode body 7 Positive electrode current collection tab 8 Negative electrode current collection tab

Claims (9)

A positive electrode having a positive electrode mixture layer containing a positive electrode active material on one side or both sides of the current collector and a negative electrode having a negative electrode mixture layer containing a negative electrode active material on one side or both sides of the current collector via a separator A spirally wound electrode body having a flat cross section wound in a spiral shape, and a lithium ion secondary battery having a non-aqueous electrolyte,
The positive electrode has a current collecting tab attached to an exposed portion where the positive electrode mixture layer is not present in at least a part of the current collector,
The negative electrode has a current collecting tab attached to an exposed portion where the negative electrode mixture layer does not exist in at least a part of the current collector,
The separator has a porous layer (I) composed of a microporous membrane made of polyolefin, and a porous layer (II) mainly containing inorganic fine particles having a heat-resistant temperature of 150 ° C. or higher.
In the wound electrode body, the porous layer (I) and the positive electrode and / or the negative electrode in the separator are attached, and the thickness of the thinnest part of the separator is 80 to 95% of the thickness of the thickest part. A lithium ion secondary battery characterized by the above.   The lithium ion secondary battery according to claim 1, wherein the porous layer (I) and the negative electrode in the separator are attached.   The negative electrode mixture layer of the negative electrode contains a material containing Si and O as constituent elements (however, the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5) as a negative electrode active material. The lithium ion secondary battery according to claim 1 or 2.   The negative electrode mixture layer of the negative electrode contains a composite of a material containing Si and O as constituent elements and a carbon material, and the composite has a surface of the material containing Si and O as constituent atoms. The lithium ion secondary battery according to claim 3, which is coated with the carbon material.   The lithium ion secondary battery according to claim 3 or 4, wherein the negative electrode mixture layer of the negative electrode further contains graphite as a negative electrode active material. The positive electrode mixture layer of the positive electrode has the following general composition formula (1)
Li _{1 + a} Ni _1-bc-d Co _b Mn _c M ¹ _d O ₂ (1)
[In the general composition formula (1), M ¹ is selected from the group consisting of Mg, Al, Ti, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Sn, W, B, P, and Bi. At least one element, −0.15 ≦ a ≦ 0.15, 0.05 ≦ b ≦ 0.4, 0.05 ≦ c ≦ 0.4, 0 ≦ d ≦ 0.03, and b + c + d The lithium ion secondary battery according to claim 1, wherein the lithium-containing composite oxide (A) represented by ≦ 0.7 is contained as a positive electrode active material. The positive electrode mixture layer of the positive electrode has the following general composition formula (2)
_{Li 1 + o Co 1-p} -q Mg p M 2 q O 2 (2)
[In the general composition formula (4), M ² is at least selected from the group consisting of Al, Ti, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Sn, W, B, P, and Bi. One element, -0.3 ≦ o ≦ 0.3, 0 ≦ p ≦ 0.1, and 0 ≦ q ≦ 0.1]
The lithium ion secondary battery of Claim 6 which further contains lithium containing complex oxide (B) represented by these as a positive electrode active material.   The lithium ion secondary battery according to any one of claims 1 to 7, wherein constant current-constant voltage charging is performed at a final voltage exceeding 4.25 V before use. A method for producing the lithium ion secondary battery according to claim 1,
A step (1) of forming a wound electrode body by winding a laminate in which a separator is disposed between a positive electrode and a negative electrode;
A step (2) of attaching the separator porous layer (I) to the positive electrode and / or the negative electrode while applying a heat press to the wound electrode body to make the cross section flat.
The method for producing a lithium ion secondary battery, wherein the heating press in the step (2) is performed under conditions of a temperature of 40 to 70 ° C. and a pressure of 1.96 to 9.80 MPa.

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