WO2017047353A1 - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

Provided is a nonaqueous electrolyte secondary battery which exhibits excellent high load characteristics, while having good charge and discharge cycle characteristics. A nonaqueous electrolyte secondary battery according to the present invention is characterized in that: a flattened electrode body having a pair of wide surfaces is contained in an outer case; the flattened electrode body is obtained by laminating a long positive electrode and a long negative electrode, with a separator being interposed therebetween, and winding the laminate into a coil; the positive electrode and the negative electrode respectively have a positive electrode collector tab and a negative electrode collector tab; at least one of the positive electrode and the negative electrode has two or more collector tabs; and the positive electrode collector tab and the negative electrode collector tab are arranged so as not to overlap with each other in a side view of the electrode body from a wide surface side.

Description

Nonaqueous electrolyte secondary battery

This invention relates to a non-aqueous electrolyte secondary battery.

Non-aqueous electrolyte secondary batteries have been widely deployed not only for consumer devices such as mobile phones and laptop computers but also for industrial applications such as electric bicycles and power storage due to their high energy density. In particular, the demand for robots such as drones and nursing aids has been greatly increasing in recent years. Applications related to these robots do not require absolute battery capacity, but both high energy density and high input / output performance are required. Especially, energy density per weight and load characteristics during discharge are required. It has become a situation. Furthermore, suppression of heat generation during large current discharge is also an important issue.

Patent Document 1 discloses that high energy density and high discharge rate characteristics can be obtained by optimizing the arrangement configuration of current collecting tabs of positive and negative electrodes. Patent Document 2 discloses a non-aqueous electrolyte secondary battery that can ensure high safety even if an internal short circuit occurs in an abnormal state in a system with high capacity and high output.

JP 2009-245839 A JP 2014-225326 A

However, since the batteries disclosed in Patent Documents 1 and 2 utilize a cylindrical iron outer can, heat dissipation from the outer can during charging and discharging under high load was not sufficient.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent high load characteristics and good charge / discharge cycle characteristics.

In the nonaqueous electrolyte secondary battery of the present invention, a flat electrode body having a pair of wide surfaces is housed in an exterior body, and the flat electrode body includes a long positive electrode and a long negative electrode. The positive electrode and the negative electrode have a positive electrode current collecting tab and a negative electrode current collecting tab, respectively, and the positive electrode and the negative electrode are wound in a spiral shape. At least one of the positive electrode and the negative electrode is 2 The positive electrode current collector tab and the negative electrode current collector tab are arranged so as not to overlap when the electrode body is viewed from the side of the wide surface. It is.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that has excellent high load characteristics and good charge / discharge cycle characteristics.

It is a top view which represents typically an example of the embodiment of the positive electrode which concerns on the nonaqueous electrolyte secondary battery of this invention. It is the II sectional view taken on the line of FIG. It is a top view which represents typically an example of the embodiment of the negative electrode which concerns on the nonaqueous electrolyte secondary battery of this invention. It is the II-II sectional view taken on the line of FIG. It is a side view which represents typically an example of the embodiment of the flat-shaped electrode body which concerns on the nonaqueous electrolyte secondary battery of this invention. It is a perspective view which represents typically an example of the embodiment of the nonaqueous electrolyte secondary battery of this invention. It is a side view which represents typically the flat electrode body which concerns on the nonaqueous electrolyte secondary battery which is a comparative example of this invention.

In the nonaqueous electrolyte secondary battery of the present invention, two or more current collecting tabs are arranged on at least one of the long positive electrode and the long negative electrode. Thereby, the current collection property in a positive electrode and / or a negative electrode can be improved, and the high load characteristic of a battery can be improved.

In addition, in an electrode body in which a long positive electrode and a long negative electrode are wound in a spiral shape, heat is generated due to current being concentrated on the current collecting tab during charging and discharging. When charging / discharging at a high load, the heat generation at the current collecting tab is further remarkable. In the present invention, by providing two or more current collecting tabs in at least one of the positive electrode and the negative electrode, it is possible to avoid current concentration on one current collecting tab and prevent remarkable heat generation. Furthermore, since the electrode body is made flat and the battery is housed in the exterior body, the surface area per volume can be increased as compared with the cylindrical battery, so that heat dissipation can be improved.

In addition, when viewed from the wide side of the flat electrode body, the current collecting tabs of the positive electrode and the negative electrode are arranged so as not to overlap, thereby increasing the battery thickness due to repeated charge / discharge and distortion of the electrode body. Therefore, it is possible to suppress the occurrence of charging / discharging reaction unevenness and to suppress deterioration of charging / discharging cycle characteristics.

In the present invention, two or more current collecting tabs are disposed on at least one of the long positive electrode and the long negative electrode. As will be described later, when the flat electrode body is viewed from the wide surface side, the number of current collecting tabs is not limited as long as the current collecting tabs do not overlap, but from the viewpoint of workability, one electrode is used. On the other hand, 5 or less is preferable, and 2 is most preferable for one electrode.

Further, as long as the electrode body has a flat shape, the outer package can be applied to either a can or a film. When a flat bottomed cylindrical can is used for the outer package, that is, when a so-called rectangular battery is used, the outer can generally has a positive electrode. The above arrangement is preferable because workability is improved. Furthermore, since aluminum (including an aluminum alloy) can be used for the outer can, it is preferable from the viewpoint of weight energy density and heat dissipation.

Hereinafter, description will be made with reference to the drawings. 1 to 5 are drawings schematically showing components according to an embodiment of the present invention having two positive electrode current collecting tabs and one negative electrode current collecting tab. FIG. 1 is a plan view of a long positive electrode before winding, and FIG. 2 is a cross-sectional view taken along the line II of FIG. The positive electrode 1 is provided with a strip-shaped positive current collector 11 and a positive electrode mixture layer 12 on both sides and partly on one side, and both ends of the positive current collector 11 are exposed to positive current collector exposed portions 11a and 11b, respectively. Have The positive electrode current collecting tabs 13a and 13b are disposed on the positive electrode current collector exposed portions 11a and 11b, respectively, and are welded by, for example, resistance welding.

FIG. 3 is a plan view of the negative electrode of the strip-shaped elongated body before winding, and FIG. 4 is a cross-sectional view taken along the line II-II in FIG. The negative electrode 2 is provided with a strip-shaped elongated negative electrode current collector 21 and a negative electrode mixture layer 22 on both surfaces and partly on one surface. The negative electrode current collector 21 has a negative electrode current collector exposed portion 21a at one end. . The negative electrode current collector tab 23 is disposed on the negative electrode current collector exposed portion 21a and is welded by, for example, resistance welding.

FIG. 5 is a side view of an electrode body in which the positive electrode shown in FIGS. 1 and 2 and the negative electrode shown in FIGS. 3 and 4 are stacked via a separator and wound into a spiral shape to form a flat shape. The electrode body 3 is wound with an insulating winding tape 31 after being wound. As shown in FIG. 5, since the electrode body 3 has a flat shape, the surface area can be increased as compared with a cylindrical electrode body having the same volume, so that heat dissipation can be improved.

The flat electrode body 3 has a pair of wide surfaces 30, two positive current collecting tabs 13 a and 13 b and one negative current collecting tab from one end in the winding axis direction of the electrode body 3. 23 protrudes. A current is supplied to the electrode body through these current collecting tabs to perform charging / discharging. As shown in FIG. 5, the positive electrode current collecting tab 13 a, the positive electrode current collecting tab 13 b, and the negative electrode current collecting tab 23 do not overlap with each other in a side view from the wide surface 30 side of the electrode body 3. This enhances the heat dissipation of the current collecting tab portion where heat tends to concentrate. In addition, by arranging the current collecting tabs in this way, variation in the thickness of the entire flat electrode body (distance from one wide surface to the other wide surface) can be suppressed, and therefore by repeated charge and discharge Since the occurrence of unevenness in the thickness of the electrode body can be suppressed and the occurrence of charge / discharge reaction unevenness due to the unevenness in thickness can also be suppressed, it is possible to suppress deterioration in cycle characteristics.

In the electrode body, the length of the wide surface in the direction perpendicular to the winding axis direction (length in the direction perpendicular to the current collecting tab; hereinafter, this length is referred to as “width”) is 20 to 90 mm. It is preferably 30 to 80 mm. This is because when the width is narrower than 30 mm, it is difficult to take out a plurality of current collecting tabs. In addition, when the width is wider than 80 mm, the ratio of the width and height of the electrode body greatly deviates from the actual value when considering the balance with the capacity described later (1.5 to 4.0 Ah). This is because it adversely affects sex. In general, in order to reduce the battery resistance, it is better to make the width of the electrode body smaller than the height. Therefore, from this viewpoint, the width of the electrode body is particularly preferably 80 mm or less.

The cross-sectional area per one current collecting tab is preferably 0.1 to 1.5 mm ² , and particularly preferably 0.15 to 1.0 mm ² . This is because when the cross-sectional area is smaller than 0.15 mm ^2, the resistance derived from the current collecting tab increases, and it is difficult to obtain high load characteristics even if the current collecting tab is increased. Further, if the cross-sectional area is larger than 1.0 mm ² , the current collecting tabs are too wide and thick, which causes problems in productivity such as weldability.

Further, in the electrode body, it is preferable that 50 to 100% of the area of the portion where the current collecting tab overlaps the electrode of different polarity through the separator in a plan view is protected with a tape or a resin film. Since the portion where the current collecting tab is attached becomes thick as an electrode, there is a possibility of causing an internal short circuit when stress is applied from the outside. When the number of current collecting tabs is increased, the risk is increased. Therefore, in order to reduce the current collecting tabs, it is preferable that the current collecting tabs be attached so as to be 50 to 100% of the overlapping portion.

[Positive electrode]
For the positive electrode according to the nonaqueous electrolyte secondary battery of the present invention, for example, a positive electrode mixture layer containing a positive electrode active material, a conductive additive, a binder, etc. is used on one side or both sides of the current collector. it can.

<Positive electrode active material>
The positive electrode active material used for the positive electrode is not particularly limited, and a generally usable active material such as a lithium-containing transition metal oxide may be used. Specific examples of the lithium-containing transition metal oxide include, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O _2. and _{Li x Ni 1-y M y} O 2, Li x Mn y Ni z Co 1-y-z O 2, Li x Mn 2 O 4, Li x Mn 2-y M y O 4 and the like. However, in each structural formula above, M is at least one metal element selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu, Zn, Al, Ti, Zr, Ge, and Cr. 0 ≦ x ≦ 1.1, 0 <y <1.0, 2.0 <z <1.0. From the viewpoint of energy density, a layered compound containing lithium and cobalt (general formula LiCo _1-y M ² _y O ₂ ; M ² is at least one metal element selected from the above-mentioned group in which Co is removed from Co, y Is the same as described above.

<Binder>
As the binder used for the positive electrode, any of a thermoplastic resin and a thermosetting resin can be used as long as it is chemically stable in the battery. For example, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), styrene-butadiene rubber (SBR), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoro Ethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), propylene- Tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, Len - methyl acrylate copolymer, ethylene - methyl methacrylate copolymer and the one or more such as Na ion crosslinked product thereof copolymer can be used.

<Conductive aid>
As a conductive support agent used for the said positive electrode, what is chemically stable should just be in a battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fiber and metal fiber; aluminum Metal powder such as powder; Conductive whisker made of carbon fluoride; Zinc oxide; Potassium titanate; Conductive metal oxide such as titanium oxide; Organic conductive materials such as polyphenylene derivatives, etc. You may use independently and may use 2 or more types together. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

<Current collector>
The current collector used for the positive electrode can be the same as that used for the positive electrode of a conventionally known non-aqueous electrolyte secondary battery. For example, an aluminum foil having a thickness of 10 to 30 μm can be used. preferable.

<Method for producing positive electrode>
For the positive electrode, for example, a paste-like or slurry-like positive electrode mixture-containing composition in which the positive electrode active material, the conductive auxiliary agent and the binder described above are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared. (However, the binder may be dissolved in a solvent.) After applying this to one or both sides of the current collector and drying, it can be produced through a process of calendering if necessary. . The manufacturing method of a positive electrode is not necessarily restricted to said method, It can also manufacture with another manufacturing method.

<Positive electrode mixture layer>
In the positive electrode mixture layer, it is preferable that the total amount of the positive electrode active material is 92 to 95% by mass, the amount of the conductive assistant is 3 to 6% by mass, and the amount of the binder is 3 to 6% by mass. In order to improve the discharge characteristics under a high load, the thickness of the positive electrode mixture layer is preferably 20 to 70 μm per side. This is because, if the positive electrode mixture layer is thinned, the maximum distance along which lithium ions move during charge / discharge can be shortened, so that the internal resistance can be kept low.

Further, the total area of the positive electrode mixture layer on the positive electrode current collector (the total area of the area occupied by the positive electrode mixture layer on one surface of the positive electrode current collector and the area occupied by the positive electrode mixture layer on the other surface) ) Is preferably 300 to 2000 cm ² , particularly preferably 500 to 1600 cm ² . This is because when the electrode area is smaller than 300 cm ^{2, the} capacity is lowered from the balance with the electrode thickness described above, and the flowing current value is also reduced, so that the effect of increasing the current collecting tab is too small. This is because if the total area of the positive electrode mixture layer is larger than 2000 cm ² , the energy density becomes too low due to the balance between the positive electrode mixture layer thickness and the capacity described above, and it becomes difficult to achieve both energy density.

The value obtained by dividing the battery capacity by the total area of the positive electrode mixture layer (referred to herein as “current density”) is preferably 2.0 to 3.5. When the current density is less than 2, the energy density is too low, and when it is more than 3.5, the polarization resistance at the time of high-load charge / discharge is increased, and the active material is easily deteriorated.

[Negative electrode]
The negative electrode according to the non-aqueous electrolyte secondary battery of the present invention has, for example, a structure having a negative electrode mixture layer containing a negative electrode active material, a binder, and a conductive auxiliary agent if necessary on one side or both sides of a current collector. Things can be used.

<Negative electrode active material>
The negative electrode active material is not particularly limited as long as it is a negative electrode active material used in conventionally known non-aqueous electrolyte secondary batteries, that is, a material capable of inserting and extracting lithium ions. For example, carbon-based materials that can occlude and release lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One kind or a mixture of two or more kinds is used as the negative electrode active material. In addition, elements such as silicon (Si), tin (Sn), germanium (Ge), bismuth (Bi), antimony (Sb), indium (In), and alloys thereof, lithium such as lithium-containing nitride or lithium-containing oxide A compound that can be charged and discharged at a low voltage close to that of a metal, or a lithium metal or a lithium / aluminum alloy can also be used as the negative electrode active material. Among these, as the negative electrode active material, a mixture of a material represented by SiO _x (0.5 ≦ x ≦ 1.5) containing silicon and oxygen as constituent elements and graphite is preferable.

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 only necessary that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5. 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.

The SiO _x is preferably a composite that is combined with a carbon material. For example, the surface of the SiO _x is preferably covered with the carbon material. Usually, since SiO _x has poor conductivity, when using it as a negative electrode active material, from the viewpoint of ensuring good battery characteristics, a conductive material (conductive aid) is used, and SiO _x in the negative electrode is electrically conductive. It is necessary to form an excellent conductive network by making good mixing and dispersion with the conductive material. 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.

<Binder>
Examples of the binder include polysaccharides such as starch, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, regenerated cellulose, and diacetyl cellulose, and modified products thereof; polyvinyl chloride, polyvinyl pyrrolidone (PVP), Thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide and their modified products; polyimide; ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber ( SBR), butadiene rubber, polybutadiene, fluororubber, polyethylene oxide and other polymers having rubber-like elasticity, and modified products thereof. It can be used either alone or in combination.

<Conductive aid>
A conductive material may be further added to the negative electrode mixture layer as a conductive aid. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery. For example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon It is possible to use one or more materials such as fiber, metal powder (powder of copper, nickel, aluminum, silver, etc.), metal fiber, polyphenylene derivative (described in JP-A-59-20971). it can. Among these, carbon black is preferably used, and ketjen black and acetylene black are more preferable.

<Current collector>
As the current collector, a copper or nickel foil, 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.

<Method for producing negative electrode>
The negative electrode is prepared, for example, by preparing a paste-like or slurry-like negative electrode mixture-containing composition in which the above-described negative electrode active material and binder, and further, if necessary, a conductive additive dispersed in a solvent such as NMP or water. It can be manufactured through a step of applying a calender treatment as necessary after applying this to one or both sides of the current collector and drying it. The manufacturing method of a negative electrode is not necessarily restricted to said manufacturing method, It can also manufacture with another manufacturing method.

<Negative electrode mixture layer>
In the negative electrode mixture layer, it is preferable that the total amount of the negative electrode active material is 80 to 99% by mass and the amount of the binder is 1 to 20% by mass. In addition, when a conductive material is separately used as a conductive auxiliary agent, these conductive materials in the negative electrode mixture layer are used in such a range that the total amount of the negative electrode active material and the binder amount satisfy the above-described preferable values. It is preferable.

In order to improve discharge characteristics under high load, the thickness of the negative electrode mixture layer is preferably 20 to 70 μm per side. This is because, when the negative electrode mixture layer is thinned, the maximum distance that lithium ions move during charge / discharge can be shortened, so that the internal resistance can be kept low. The material represented by SiO _x can have a higher capacity than graphite, which is the most common negative electrode active material. Therefore, when the material represented by SiO _x is contained in the negative electrode active material, the total amount of the negative electrode active material can be reduced, and thus the negative electrode mixture layer can be easily thinned.

[Non-aqueous electrolyte]
For the non-aqueous electrolyte according to the non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte obtained by dissolving a lithium salt in an organic solvent can be used.

The lithium salt used in the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 7), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group]; Can be used.

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

The organic solvent used in the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene 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; dimethoxyethane, Chain ethers such as 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; ethylene And sulfites such as glycol sulfite, and the like. These may be used as a mixture of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination such as a mixed solvent of ethylene carbonate and chain carbonate that can obtain high conductivity.

[Separator]
The separator according to the non-aqueous electrolyte secondary battery has a property that the pores are closed at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower) (ie, shutdown function). It is preferable that a separator used in an ordinary nonaqueous electrolyte secondary battery, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be.

The thickness of the separator is preferably larger than 6 μm and smaller than 20 μm.

Further, the thickness of the separator is more preferably smaller than 16 μm and further preferably smaller than 14 μm from the viewpoint of improving the volumetric energy density of the battery. Conventionally, remarkable heat generation occurs due to current concentration on the positive electrode current collecting tab portion, so there is a concern about internal short circuit due to thermal contraction of the separator at the location, and thermal contraction is prevented by increasing the thickness of the separator. . In the present invention, when two or more positive electrode current collecting tabs are provided, it is possible to prevent heat from concentrating on one positive electrode current collecting tab. Therefore, it is possible to use a separator thinner than the conventional one, and further contribute to the improvement of the volume energy density.

Further, the thickness of the separator is more preferably larger than 8 μm because of ease of handling.

A separator for a non-aqueous electrolyte secondary battery includes a porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or less, a resin that does not melt at a temperature of 150 ° C. or less, or an inorganic filler having a heat resistant temperature of 150 ° C. or more. It is preferable to use a laminated separator having a porous layer (II) containing as a main component. Here, the “melting point” means the melting temperature measured using a differential scanning calorimeter (DSC) in accordance with the provisions of JIS K 7121. Further, “does not melt at a temperature of 150 ° C. or lower” means that the melting temperature measured using DSC exceeds 150 ° C. according to the provisions of JIS K 7121, such as 150 ° C. or lower when the melting temperature is measured. This means that the melting behavior is not exhibited at the temperature. Furthermore, “the heat resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

The porous layer (I) relating to the laminated separator is mainly for ensuring a shutdown function, and the non-aqueous electrolyte secondary battery is a resin that is a main component of the porous layer (I). When the temperature exceeds the melting point, the resin related to the porous layer (I) melts and closes the pores of the separator, thereby causing a shutdown that suppresses the progress of the electrochemical reaction.

Examples of the resin having a melting point of 140 ° C. or lower, which is the main component of the porous layer (I), include PE, and the form thereof includes a microporous membrane used as a separator for the above-described non-aqueous electrolyte secondary battery, and a nonwoven fabric. And the like obtained by applying a dispersion containing PE particles to a base material and drying the substrate. Here, in all the constituent components of the porous layer (I), the volume of the resin having a main melting point of 140 ° C. or less is 50% by volume or more, and more preferably 70% by volume or more. For example, when the porous layer (I) is formed of the microporous film of PE, the volume of the resin having a melting point of 140 ° C. or lower is 100% by volume.

The porous layer (II) according to the multilayer 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 nonaqueous electrolyte secondary battery rises. The function is secured by a resin that does not melt at a temperature of 150 ° C. or lower or an inorganic filler having a heat resistant temperature of 150 ° C. or higher. That is, when the battery becomes high temperature, even if the porous layer (I) shrinks, the porous layer (II) which does not easily shrink can directly generate positive and negative electrodes that can be generated when the separator is thermally contracted. It is possible to prevent a short circuit due to the contact. 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.

When the porous layer (II) is mainly formed of a resin that does not melt at a temperature of 150 ° C. or lower, for example, a microporous film formed of a resin that does not melt at a temperature of 150 ° C. or lower (for example, the aforementioned battery made of PP A microporous membrane for coating) is applied to the porous layer (I), and a dispersion containing resin particles that do not melt at a temperature of 150 ° C. or lower is applied to the porous layer (I) and dried to be porous. An application lamination type form in which the porous layer (II) is formed on the surface of the layer (I) is exemplified.

Resins that do not melt at temperatures below 150 ° C include PP; crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensation And various crosslinked polymer fine particles; polysulfone; polyether sulfone; polyphenylene sulfide; polytetrafluoroethylene; polyacrylonitrile; aramid; polyacetal;

When using resin particles that do not melt at a temperature of 150 ° C. or lower, the average particle size is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, It is preferably 10 μm or less, and more preferably 2 μm or less. The average particle diameter of the various particles referred to in the present specification is, for example, an average particle measured by dispersing these particles in a medium in which the particles are not dissolved using a laser scattering particle size distribution analyzer “LA-920” manufactured by Horiba, Ltd. The diameter D is 50%.

When the porous layer (II) is mainly formed of an inorganic filler having a heat resistant temperature of 150 ° C. or higher, for example, a dispersion containing an inorganic filler having a heat resistant temperature of 150 ° C. or higher is applied to the porous layer (I). Examples of the coating-laminated type in which the porous layer (II) is formed by drying.

The inorganic filler related to the porous layer (II) has a heat-resistant temperature of 150 ° C. or higher, is stable with respect to the non-aqueous electrolyte of the battery, and is electrochemically stable that is not easily oxidized or reduced in the battery operating voltage range. However, fine particles are preferable from the viewpoint of dispersion, and alumina, silica, and boehmite are preferable. Alumina, silica, and boehmite have high oxidation resistance, and the particle size and shape can be adjusted to the desired numerical values, making it easy to control the porosity of the porous layer (II) with high accuracy. It becomes. As the inorganic filler having a heat resistant temperature of 150 ° C. or higher, for example, one of the above-mentioned examples may be used alone, or two or more may be used in combination. Further, an inorganic filler having a heat resistant temperature of 150 ° C. or higher may be used in combination with a resin that does not melt at a temperature of 150 ° C. or lower.

There is no restriction | limiting in particular about the shape of the inorganic filler whose heat resistant temperature which concerns on porous layer (II) is 150 degreeC or more, A substantially spherical shape (a true spherical shape is included), a substantially ellipsoid shape (an ellipsoid shape is included), a board Various shapes such as shapes can be used.

Further, the average particle diameter of the inorganic filler 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 filler having a heat resistant temperature of 150 ° C. or higher is too large, the electrical characteristics are likely to be deteriorated. Therefore, the average particle diameter is preferably 5 μm or less, and more preferably 2 μm or less.

In the porous layer (II), the resin that does not melt at a temperature of 150 ° C. or lower and the inorganic filler having a heat resistant temperature of 150 ° C. or higher are mainly contained in the porous layer (II). The amount in (II) [when the porous layer (II) contains only one of a resin that does not melt at a temperature of 150 ° C. or less and an inorganic filler that has a heat resistant temperature of 150 ° C. or more, is the amount, If both are included, the total amount. The same applies hereinafter in the porous layer (II) of the resin that does not melt at a temperature of 150 ° C. or lower and the inorganic filler having a heat resistant temperature of 150 ° C. or higher. ] Is 50% by volume or more in the total volume of the constituent components of the porous layer (II), preferably 70% by volume or more, more preferably 80% by volume or more, and 90% by volume or more. More preferably it is. By making the heat-resistant material 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 nonaqueous electrolyte 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 that the porous layer (II) also contains an organic binder, in the porous layer (II) of a resin that does not melt at a temperature of 150 ° C. or less and an inorganic filler having a heat resistant temperature of 150 ° C. or more. The amount is preferably 99.5% by volume or less in the total volume of the constituent components of the porous layer (II).

In the porous layer (II), a resin that does not melt at a temperature of 150 ° C. or less or an inorganic filler having a heat resistant temperature of 150 ° C. or higher is bound, or the porous layer (II) and the porous layer (I) It is preferable to contain an organic binder for integration. Organic binders include ethylene-vinyl acetate copolymers (EVA, structural units derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, 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 rubber, and SBR are preferable. Examples of such highly flexible organic binders include EVA “Evaflex Series” from Mitsui DuPont Polychemical Co., Ltd., EVA from Nippon Unicar Co., Ltd., and “Everflex-EEA Series” ethylene-acrylic acid copolymer from Mitsui DuPont Polychemical Co. ”EEA of Nihon Unicar Company,“ Daiel Latex Series ”of fluorine rubber of Daikin Industries, Ltd., SBR“ TRD-2001 ”of JSR Corporation, SBR“ BM-400B ”of Zeon Corporation.

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

The coating-laminated separator is, for example, a composition for forming a porous layer (II) containing a resin particle that does not melt at a temperature of 150 ° C. or lower, an inorganic filler having a heat resistant temperature of 150 ° C. or higher (liquid such as slurry). By applying the composition, etc.) to the surface of the membrane (microporous membrane, nonwoven fabric, etc.) constituting the porous layer (I) and drying at a predetermined temperature to form the porous layer (II) Can be manufactured.

The composition for forming the porous layer (II) contains resin particles that do not melt at a temperature of 150 ° C. or lower and / or an inorganic filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder as necessary. Is dispersed in a solvent (including a dispersion medium; the same shall apply hereinafter). The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) can uniformly disperse resin particles and inorganic filler that do not melt at a temperature of 150 ° C. or lower, and can dissolve or disperse the organic binder uniformly. Common organic solvents such as aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; are preferably used. 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) has a solid content containing, for example, a resin particle that does not melt at a temperature of 150 ° C. or lower and / or an inorganic filler having a heat resistant temperature of 150 ° C. or higher, and an organic binder. It is preferable to set it to 80 mass%.

In the laminated 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, the porous layer (I) may be configured on both sides of the porous layer (II), or the porous layer (II) may be disposed on both sides of the porous layer (I). However, increasing the number of layers may increase the thickness of the separator and increase the internal resistance of the battery or decrease the energy density. Therefore, it is not preferable to increase the number of layers. The total number of layers of the porous layer (I) and the porous layer (II) is preferably 5 or less.

As described above, the thickness of the entire separator can be reduced according to the present invention. However, when the laminated separator is used, the effect of suppressing thermal shrinkage is extremely high, and therefore the thickness of the separator is further reduced. Is possible.

Specifically, the thickness of the porous layer (I) can be 5 to 14 μm, the thickness of the porous layer (II) can be 1 to 5 μm, and the total thickness can be 6 to 15 μm. As a result, the thickness of the separator can be further reduced, and the distance between the positive and negative electrodes can be shortened, so that the internal resistance of the battery can be kept low.

The porosity of the separator as a whole is preferably 30% or more in a dry state in order to ensure the amount of electrolyte retained and to 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 obtaining the sum for each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula (1).

P = {1-m / (Σaiρi × t)} × 100 mm (1)

Here, in the formula (1), ai: the ratio of the component i expressed in mass%, ρi: the density of the component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ) , T is the thickness (cm) of the separator.

In the case of the multilayer separator, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (I), and t is the thickness of the porous layer (I) ( cm), the porosity: P (%) of the porous layer (I) can also be obtained using the formula (1). The porosity of the porous layer (I) obtained by this method is preferably 30 to 70%.

Further, in the case of the laminated separator, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness of the porous layer (II) ( cm), the porosity: P (%) of the porous layer (II) can also be obtained using the formula (1). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

The separator preferably has high mechanical strength. For example, the puncture strength is preferably 3N or more. For example, when SiO _x having a large volume change due to charge / discharge is used as the negative electrode active material, mechanical damage is also applied to the facing separator due to expansion / contraction of the entire negative electrode by repeating charge / discharge. If the piercing strength of the separator is 3N or more, good mechanical strength is ensured, and mechanical damage to the separator can be reduced.

Examples of the separator having a puncture strength of 3N or more include the above-described laminated separator, and in particular, an inorganic filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower. A separator in which a porous layer (II) containing as a main component is laminated is preferable. This is presumably because the mechanical strength of the separator can be increased by supplementing the mechanical strength of the porous layer (I) because the inorganic filler has high mechanical strength.

The piercing strength can be measured by the following method. A separator is fixed on a plate having a hole with a diameter of 2 inches so as not to be wrinkled or bent, and a semicircular metal pin having a tip diameter of 1.0 mm is lowered onto a measurement sample at a speed of 120 mm / min. Measure the force when making a hole in the separator 5 times. And an average value is calculated | required about the measurement of 3 times except the maximum value and the minimum value among the said measurement values of 5 times, and this is made into the piercing strength of a separator.

The positive electrode, the negative electrode, and the separator are stacked in a spiral shape with a separator interposed between the positive electrode and the negative electrode. Used for the next battery.

In the electrode body, a porous layer (II) mainly containing an inorganic filler having a heat resistant temperature of 150 ° C. or more in the porous separator (I) mainly comprising a resin having a melting point of 140 ° C. or less. ) Is preferably disposed so that the porous layer (II) faces at least the positive electrode. In this case, since the porous layer (II) that includes an inorganic filler having a heat resistant temperature of 150 ° C. or more as a main component and more excellent in oxidation resistance faces the positive electrode, oxidation of the separator by the positive electrode can be better suppressed, It is possible to further improve the storage characteristics and charge / discharge cycle characteristics of the battery at high temperatures. In addition, additives such as vinylene carbonate and cyclohexylbenzene can be added to the non-aqueous electrolyte to further improve various battery characteristics. When such additives are added, a film is formed on the positive electrode side. As a result, the pores of the separator may be clogged and the battery characteristics may be deteriorated. Therefore, an effect of suppressing clogging of pores can be expected by causing the relatively porous porous layer (II) to face the positive electrode.

The non-aqueous electrolyte secondary battery of the present invention can be used with the upper limit voltage of charging being about 4.2 V as in the case of the conventional non-aqueous electrolyte secondary battery, but the upper limit voltage of charging is higher than this. It is also possible to use it by setting it to 3 V or more, so that it is possible to stably exhibit excellent characteristics even if it is repeatedly used over a long period of time while increasing the capacity. In addition, it is preferable that the upper limit voltage of charge of a nonaqueous electrolyte secondary battery is 4.7V or less.

The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as conventionally known non-aqueous electrolyte secondary batteries. Since the present invention can minimize the increase in the number of parts in the battery, in particular, a device that requires a high capacity for a limited volume, for example, a mobile device, a small device, and a multi-cell combination. This is particularly effective when the volumetric energy density is 350 to 800 Wh / L, such as for robot applications. Further, the non-aqueous electrolyte secondary battery of the present invention is well characterized when the battery capacity is 1.0 to 5.0 Ah when measured under the conditions described later (described in the examples), particularly 1.5 to 4 Optimal characteristics in the range of 0.0 Ah. In applications such as robots, the battery capacity of the present invention is well suited because the absolute battery capacity does not need to be increased in consideration of its usage.

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 positive electrode>
100 parts by mass of a positive electrode active material obtained by mixing LiCoO ₂ and Li _1.0 Ni _0.5 Co _0.2 Mn _0.3 O _{2 at} a ratio (mass ratio) of 8: 2, and 10 parts by mass of PVDF as a binder. 20 parts by weight of NMP solution contained at a concentration of 1%, 1 part by weight of artificial graphite and 1 part by weight of ketjen black, which are conductive assistants, are kneaded using a biaxial kneader, and NMP is added to adjust the viscosity. Thus, a positive electrode mixture-containing paste was prepared.

As shown in FIG. 1 and FIG. 2, the positive electrode mixture-containing paste is applied to both surfaces and a part of one surface of an aluminum foil (positive electrode current collector) having a thickness of 12 μm, followed by vacuum drying at 120 ° C. for 12 hours. Then, a positive electrode mixture layer was formed on both surfaces of the aluminum foil. Then, the press process was performed and the thickness and density of the positive mix layer were adjusted. The positive electrode mixture layer in the obtained positive electrode had a thickness of 40 μm on one side. As shown in FIGS. 1 and 2, by welding aluminum positive electrode current collecting tabs (width 5 mm, thickness 0.08 mm, cross-sectional area 0.4 mm ² ) one by one to the aluminum foil exposed portions at both ends, A strip-like positive electrode having a length of 1000 mm and a width of 54 mm having two positive electrode current collecting tabs was produced. Further, the total area of the positive electrode mixture layer at this time was 820 cm ² in total on both surfaces.

<Production of negative electrode>
A composite in which the surface of SiO having an average particle diameter D50% 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% by mass), and graphite having an average particle diameter D50% of 16 μm A mixture in which the amount of the composite having the SiO surface coated with a carbon material is 3.75% by mass: 97.5 parts by mass, SBR as a binder: 1.5 parts by mass, and a thickener CMC: 1 part by mass of water was added and mixed to prepare a negative electrode mixture-containing paste.

The negative electrode mixture-containing paste was applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm as shown in FIGS. 3 and 4 and then vacuum-dried at 120 ° C. for 12 hours to obtain a copper foil. A negative electrode mixture layer was formed on both sides and a part of one side. Then, press treatment is performed to adjust the thickness and density of the negative electrode mixture layer, and a negative electrode current collector tab made of nickel is welded to the exposed portion of the copper foil as shown in FIGS. A strip-shaped negative electrode having a width of 990 mm and a width of 55 mm was produced. The negative electrode mixture layer in the obtained negative electrode had a thickness per side of 45 μm.

<Preparation of non-aqueous electrolyte>
LiPF ₆ is dissolved at a concentration of 1.1 mol / L in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 3: 7, and vinylene carbonate in an amount of 2% by mass and fluoroethylene carbonate in an amount of 2% by mass are obtained. Were added to prepare a non-aqueous electrolyte.

<Preparation of separator>
To 5 kg of plate boehmite (average particle diameter 1 μm, aspect ratio 10), 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, and the internal volume is 20 L. Dispersion was prepared by crushing for 10 hours with a ball mill with 40 rotations / minute. 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 obtain uniform porosity. A slurry for forming a quality layer (II) (solid content ratio 50 mass%) was prepared.

Corona discharge treatment (discharge amount: 40 W · min / m 2) on one side of the porous layer (I) PE microporous film (thickness 10 μm, porosity 40%, average pore size 0.08 μm, PE melting point 135 ° C.) The porous layer (II) forming slurry is applied to the treated surface with a micro gravure coater and dried to form a porous layer (II) having a thickness of 2 μm on one side of the separator. A mold separator was produced.

<Battery assembly>
As shown in FIG. 5, the strip-shaped positive electrode is stacked on the strip-shaped negative electrode via the laminated separator (porosity: 42%), wound in a spiral shape, and then added to form a flat shape. The electrode body was pressed to be fixed with an insulating tape made of polypropylene. At this time, the flat electrode body was in a position where the current collecting tabs did not overlap in a side view from the wide surface as shown in FIG. The wide surface dimensions of the electrode body at this time were 50 mm in the width direction (direction perpendicular to the winding axis direction) and 58 mm in the height direction (direction parallel to the winding axis direction).

Next, the wound electrode body is inserted into a rectangular can made of aluminum alloy having an outer dimension of thickness 4.8 mm, width 57 mm, and height 60 mm, and the current collecting tab is welded to each other. The plate was welded to the open end of the square can. Thereafter, the non-aqueous electrolyte was injected from an inlet provided in the lid plate, and the inlet was sealed to obtain a non-aqueous electrolyte secondary battery 100 having an appearance shown in FIG.

The non-aqueous electrolyte secondary battery 100 has an outer can 111 and a cover plate 121, which also serve as a positive electrode terminal. The outer can 111 includes a pair of side surfaces 112, a pair of wide surfaces 113, and a bottom surface. The wide surface 113 has a cleavage groove 114 that operates as an explosion-proof mechanism when the internal pressure of the battery increases. The lid 121 is inserted into the opening of the outer can 111, and the joint of the two is welded to seal the opening of the outer can 111 and seal the inside of the battery. The lid 121 is provided with a non-aqueous electrolyte inlet, and the non-aqueous electrolyte inlet is welded and sealed by, for example, laser welding in a state where the sealing member 122 is inserted. Airtightness is ensured. A stainless steel terminal 123 is attached to the lid 121 via an insulating packing 124 made of PP, and a lead plate is attached to the terminal 123 via an insulator inside the battery.

Although not shown, the positive electrode current collecting tab is directly welded to the lid body 121 so that the outer can 111 and the lid body 121 function as a positive electrode terminal, and the negative electrode current collecting tab is welded to a lead plate inside the battery. The terminal 123 functions as a negative electrode terminal by conducting with the terminal 123 through the lead plate.

Example 2
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that a PE microporous membrane (thickness 20 μm) was used as the separator.

Example 3
A strip-shaped positive electrode was produced in the same manner as in Example 1 except that the size was changed to 700 mm in length and 54 mm in width. The total area of the positive electrode mixture layer at this time was 660 cm ² in total on both sides.

Further, a strip-shaped negative electrode was produced in the same manner as in Example 1 except that the size was changed to 800 mm in length and 55 mm in width.

A flat electrode body was produced in the same manner as in Example 1 except that the belt-like positive electrode and the belt-like negative electrode were used. The wide surface dimensions of the electrode body at this time were 35 mm in the width direction and 58 mm in the height direction.

And the nonaqueous electrolyte secondary battery was carried out in the same manner as in Example 1 except that the flat electrode body was inserted into an aluminum alloy rectangular can having a thickness of 4.8 mm, a width of 38 mm, and a height of 60 mm. Was made.

Example 4
A belt-like positive electrode was produced in the same manner as in Example 1 except that the size was changed to 1600 mm in length and 54 mm in width. The total area of the positive electrode mixture layer at this time was 1560 cm ² in total on both sides.

Further, a strip-shaped negative electrode was produced in the same manner as in Example 1 except that the size was changed to 1700 mm in length and 55 mm in width.

A flat electrode body was produced in the same manner as in Example 1 except that the belt-like positive electrode and the belt-like negative electrode were used. The wide surface dimensions of the electrode body at this time were 75 mm in the width direction and 58 mm in the height direction.

And the nonaqueous electrolyte secondary battery was carried out in the same manner as in Example 1 except that the flat electrode body was inserted into a square can made of an aluminum alloy having a thickness of 4.8 mm, a width of 78 mm, and a height of 60 mm. Was made.

Comparative Example 1
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the electrode body was formed in a cylindrical shape and the exterior body was changed to a conventionally known cylindrical shape.

Comparative Example 2
A belt-like positive electrode was produced in the same manner as in Example 1 except that the positive electrode current collecting tab 13b was not provided, and this positive electrode was used. In addition, a PE microporous film (thickness 20 μm) was used. A non-aqueous electrolyte secondary battery was produced in the same manner as described above.

Comparative Example 3
The same belt-like positive electrode, belt-like negative electrode, and separator as used in Example 1 are stacked, and the positive electrode winding start position is changed to that of Example 1, and the positive electrode current collecting tab 213a on the outermost peripheral side of the electrode body, and the electrode A flat electrode body 203 was produced with the positive electrode current collecting tab 213b on the innermost peripheral side of the body arranged as shown in FIG.

A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this flat electrode body 203 was used.

Comparative Example 4
A nonaqueous electrolyte secondary battery was produced in the same manner as in Comparative Example 3 except that the separator was changed to a PE microporous membrane (thickness 20 μm).

Each non-aqueous electrolyte secondary battery in Examples and Comparative Examples was evaluated by the following evaluation methods. Tables 1 and 2 show the configuration of each battery, and Table 3 shows the evaluation results.

<Battery capacity>
About each battery of an Example and a comparative example, it was set as the state fully discharged once by discharging constant current (it is hereafter described as CC) to 2.75V with the electric current value of 1C. Next, each battery was charged with a constant current and a constant voltage (hereinafter referred to as CCCV) up to 4.35V. The CC charging current value was 1 C, and the charging end current value was 0.05 C. Then, CC discharge was performed to 2.75V with the electric current value of 0.2C about each battery, and the discharge capacity at that time was measured. The capacity at this time was defined as the battery capacity.

<Discharge load characteristics>
About each battery of an Example and a comparative example, it was set as the state fully discharged once by CC discharging to 2.75V with the electric current value of 1C. Next, CCCV charge was performed up to 4.35V for each battery. The CC charging current value was 1 C, and the charging end current value was 0.05 C. Then, CC discharge was performed to 2.75V with the electric current value of 0.2C about each battery, and the discharge capacity at that time was measured.

Next, CCCV charging was performed again under the same conditions for each battery, and CC discharge was performed to a current value of 10 C to 2.75 V, and the discharge capacity and the surface temperature of the battery were evaluated.

As the high load discharge characteristics evaluation, values (10C / 0.2C discharge capacity ratio) obtained by dividing the discharge capacity at the time of 10C discharge by the discharge capacity at the time of 0.2C discharge were calculated for each battery of the example and the comparative example. . The 10 C / 0.2 C discharge capacity ratio in Table 2 shows the relative value when the result of the battery of Example 1 is set to 100 for each battery.

<1 kHz AC resistance [impedance (Imp.)]>
The 1 kHz AC resistance of each of the nonaqueous electrolyte secondary batteries in Examples and Comparative Examples was obtained by performing CC discharge to 2.75 V at a current value of 1 C, performing CCCV charge to 4.35 V, and then measuring resistance manufactured by HIOKI It measured at 25 degreeC using the machine "HiTESTER".

<Measurement of battery thickness>
The thickness of each of the nonaqueous electrolyte secondary batteries in Examples and Comparative Examples was determined by using a thickness gauge (measurement part φ10 mm flat circle) manufactured by Mitutoyo Co., Ltd. It measured with the location corresponding to the current collection tab of an electrode body of a shape. Table 3 shows the maximum value of the thickness of the central portion and the thickness of the portion corresponding to the current collecting tab position.

<Charge / discharge cycle characteristics>
About each nonaqueous electrolyte secondary battery of an Example and a comparative example, it was made into the state discharged completely once by CC discharging to 2.75V with the electric current value of 1C. Next, CCCV charge was performed up to 4.35V for each battery. The CC charging current value was 1 C, and the charging end current value was 0.05 C. Then, CC discharge was performed to 2.75V with the electric current value of 5C about each battery, and the initial stage discharge capacity in that case was calculated | required. Then, this charging / discharging condition was made into 1 cycle, and about each battery, the discharge capacity when repeating 500 cycles charging / discharging was calculated | required. In Table 3, the value obtained by dividing the discharge capacity after 500 cycles by the initial discharge capacity is shown as a percentage (capacity maintenance ratio) for each battery.

As in Examples 1 to 4, the non-aqueous electrolyte secondary battery in which the electrode body is flat, uses two positive electrode current collecting tabs, and is arranged at a position where the current collecting tabs do not overlap when viewed from the wide side. Since the impedance was low, the 10C / 0.2C discharge capacity ratio was high, and the temperature rise on the battery surface was also suppressed. In addition, the difference between the central thickness and the maximum thickness of the wide surface of the battery is small, and there is little unevenness in the thickness of the wide surface, so there is less distortion of the electrode body due to the bias in the electrode body during charging and discharging, resulting in high cycle capacity. A retention rate was obtained.

The battery of Comparative Example 1 having a cylindrical electrode body was poor in heat dissipation as compared with the battery of Example 1 having a flat electrode body, and the temperature increased during high load discharge. Further, the poor heat dissipation has a negative effect on the charge / discharge cycle characteristics. The battery of Comparative Example 2 having one current collecting tab for both the positive electrode and the negative electrode has a high impedance, and thus has a small capacity during discharge under a high load. The batteries of Comparative Examples 3 and 4 having the electrode bodies arranged so that the two positive electrode current collecting tabs overlap each other when viewed from the side have a low capacity retention rate when evaluating charge / discharge cycle characteristics. In the batteries of Comparative Examples 3 and 4, since the flat surface of the flat electrode body has a thickness unevenness, a charge / discharge capacity loss occurred while repeating the charge / discharge cycle, and the capacity retention rate was considered to be low.

The present invention can be implemented in other forms as long as it does not depart from the spirit of the present invention. The embodiments disclosed in the present application are examples, and the present invention is not limited to these embodiments. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. included.

This invention is applied to a non-aqueous electrolyte secondary battery.

DESCRIPTION OF SYMBOLS 1 Positive electrode 13a, 13b Positive electrode current collection tab 2 Negative electrode 3 Flat electrode body 30 Wide surface 100 Nonaqueous electrolyte secondary battery

Claims (8)

1. A flat electrode body having a pair of wide surfaces is housed in the exterior body,
   The flat electrode body is formed by laminating a long positive electrode and a long negative electrode via a separator and wound in a spiral shape,
   The positive electrode and the negative electrode each have a positive electrode current collecting tab and a negative electrode current collecting tab,
   At least one of the positive electrode and the negative electrode has two or more current collecting tabs,
   The non-aqueous electrolyte secondary battery, wherein the positive electrode current collecting tab and the negative electrode current collecting tab are arranged so as not to overlap when the electrode body is viewed from the side of the wide surface.
2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the battery capacity when measured under the following conditions is 1.5 to 4.0 Ah.
   <Battery capacity measurement conditions>
   By discharging at a constant current up to 2.75 V at a current value of 1 C, the battery is completely discharged once. Next, constant current constant voltage charging is performed up to 4.35V. The constant current charging current value is 1 C, and the charging end current value is 0.05 C. Subsequently, constant current discharge is performed at a current value of 0.2 C up to 2.75 V, and the discharge capacity at that time is defined as battery capacity.
3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the wide surface has a length in a direction perpendicular to a winding axis direction of 30 to 80 mm.
4. 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the separator has a thickness of 20 μm or less.
5. The separator is
   A porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower;
   Porous layer (II) mainly comprising a resin that does not melt at a temperature of 150 ° C. or less or an inorganic filler having a heat resistant temperature of 150 ° C. or more
   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, which is a laminated separator having
6. The positive electrode has a positive electrode mixture layer on one side or both sides of a positive electrode current collector,
   6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thickness of the positive electrode mixture layer is 20 to 70 μm on one side.
7. The positive electrode has a positive electrode mixture layer on one side or both sides of a positive electrode current collector,
   7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the total area of the positive electrode mixture layer on the positive electrode current collector is 300 to 2000 cm ² .
8. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein each of the positive electrode current collecting tab and the negative electrode current collecting tab has a cross-sectional area of 0.15 to 1.0 mm ² .

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