JP6754768B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery.

Due to its high energy density, non-aqueous electrolyte secondary batteries have been widely deployed not only in consumer devices such as mobile phones and laptop computers, but also in industrial applications such as electric bicycles and electric power storage. In particular, demand for robot applications such as drones and nursing care aids has been increasing significantly in recent years. In applications related to these robots, although absolute battery capacity is not required, both high energy density and high input / output performance are required, and in particular, it is necessary to improve the energy density per weight and the load characteristics during discharge. The situation is. Furthermore, suppressing 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 together by optimizing the arrangement configuration of the current collecting tabs of the positive and negative electrodes. Further, Patent Document 2 discloses a non-aqueous electrolyte secondary battery capable of ensuring high safety even if an internal short circuit occurs in an abnormal situation in a system having a high capacity and a high output.

Japanese Unexamined Patent Publication No. 2009-245839 Japanese Unexamined Patent Publication No. 2014-225326

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 a high load is 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 non-aqueous electrolyte secondary battery of the present invention, a flat electrode body having a pair of wide surfaces is housed inside the exterior body, and the flat electrode body has a long positive electrode and a long negative electrode. It is laminated via a separator and wound in a spiral shape, and the positive electrode and the negative electrode have a positive electrode current collecting tab and a negative electrode current collecting tab, respectively, and at least one of the positive electrode and the negative electrode is 2 It has the above-mentioned current collection tabs, and is characterized in that the positive electrode current collection tab and the negative electrode current collection tab are arranged so as not to overlap when the electrode body is viewed from the wide surface side. Is.

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

It is a top view schematically showing an example of the embodiment of the positive electrode which concerns on the non-aqueous electrolyte secondary battery of this invention. FIG. 1 is a cross-sectional view taken along the line II of FIG. It is a top view schematically showing an example of embodiment of the negative electrode which concerns on the non-aqueous electrolyte secondary battery of this invention. FIG. 3 is a sectional view taken along line II-II of FIG. It is a side view schematically showing an example of embodiment of the flat electrode body which concerns on the non-aqueous electrolyte secondary battery of this invention. It is a perspective view which shows an example of embodiment of the non-aqueous electrolyte secondary battery of this invention schematically. It is a side view which shows typically the flat electrode body which concerns on the non-aqueous electrolyte secondary battery which is a comparative example of this invention.

In the non-aqueous electrolyte secondary battery of the present invention, two or more current collecting tabs are arranged on at least one of a long positive electrode and a long negative electrode. As a result, the current collecting property at the positive electrode and / or the negative electrode can be improved to improve the high load characteristics of the battery.

In the electrode body in which the long positive electrode and the long negative electrode are wound in a spiral shape, heat is generated by concentrating the current on the current collecting tab during charging and discharging. When charging / discharging with a high load, heat generation at the current collector tab becomes more remarkable. In the present invention, by providing two or more current collecting tabs on 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. Further, by forming the electrode body into a flat shape and using the battery housed in the outer body, the surface area per the same volume can be increased as compared with the cylindrical battery, so that the heat dissipation can be improved.

In addition, by arranging the current collecting tabs of the positive electrode and the negative electrode so that they do not overlap when viewed from the wide surface side of the flat electrode body, the battery thickness increases and the electrode body is distorted due to repeated charging and discharging. This can be reduced, which makes it possible to suppress the occurrence of uneven charge / discharge reaction and suppress the deterioration of charge / discharge cycle characteristics.

In 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. As will be described later, when the flat electrode body is viewed from the wide surface side, any number of current collecting tabs may be used as long as the current collecting tabs do not overlap, but from the viewpoint of workability, one electrode can be used. On the other hand, 5 or less is preferable, and 2 is most preferable for one electrode.

Further, if the electrode body has a flat shape, the outer body can be a can or a film. When a flat-shaped bottomed tubular can is used for the exterior body, that is, when a so-called square battery is used, the exterior can generally has a positive electrode, so the positive electrode current collector tab is set to 2. It is preferable to arrange the above arrangements because the workability is improved. Further, 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, in which two positive electrode current collecting tabs and one negative electrode current collecting tab are used. FIG. 1 is a plan view of a positive electrode in a long state before winding, and FIG. 2 is a sectional view taken along line II of FIG. The positive electrode 1 is provided with a positive electrode mixture layer 12 on both sides and a part of the positive electrode current collector 11 of a strip-shaped long body, and both ends of the positive electrode current collector 11 are exposed portions 11a and 11b of the positive electrode current collector, respectively. Has. The positive electrode current collector tabs 13a and 13b are arranged 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 sectional view taken along line II-II of FIG. The negative electrode 2 is provided with a negative electrode mixture layer 22 on both sides and a part of the negative electrode current collector 21 of a strip-shaped long body, and 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 arranged 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 laminated via a separator and wound in a spiral shape to form a flat shape. The electrode body 3 is wound with an insulating winding tape 31 after being wound. By forming the electrode body 3 into a flat shape as shown in FIG. 5, the surface area can be increased as compared with the cylindrical electrode body having the same volume, so that the heat dissipation can be improved.

The flat electrode body 3 has a pair of wide surfaces 30, two positive electrode current collecting tabs 13a and 13b and one negative electrode current collecting tab from one end in the winding axis direction of the electrode body 3. 23 is protruding. A current is passed through these current collecting tabs to the electrode body to charge and discharge. As shown in FIG. 5, the positive electrode current collecting tab 13a, the positive electrode current collecting tab 13b, and the negative electrode current collecting tab 23 do not overlap each other when viewed 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 each current collecting tab 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, so that charging and discharging are repeated. Since the occurrence of uneven thickness of the electrode body can be suppressed and the occurrence of uneven charge / discharge reaction due to uneven thickness can be suppressed, deterioration of cycle characteristics can be suppressed.

In the electrode body, the length in the direction perpendicular to the winding axis direction of the wide surface (the 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, and particularly preferably 30 to 80 mm. This is because if the width is narrower than 30 mm, it becomes difficult to take out a plurality of current collecting tabs. Further, when the width becomes wider than 80 mm, the ratio of the width and the height of the electrode body greatly deviates from the realistic value when considering the balance with the capacitance (1.5 to 4.0 Ah) described later, and the production This is because it has an adverse effect on sex. Generally, in order to reduce the battery resistance, the width of the electrode body should be smaller than the height. Therefore, from this viewpoint as well, the width of the electrode body is particularly preferably 80 mm or less.

Sectional area per the current collector tabs one is preferably 0.1 to 1.5 mm ^2, particularly preferably 0.15~1.0mm ^2. This is because if the cross section is smaller than 0.15 mm ^2, the resistance derived from the current collecting tab becomes large, and it is difficult to obtain high load characteristics even if the number of current collecting tabs is increased. Further, if the cross-sectional area is larger than 1.0 mm ² , the width and thickness of the current collecting tab become too large, which causes problems in productivity such as weldability.

Further, in the electrode body, it is preferable that 50 to 100% of the area where the current collecting tab overlaps the electrodes having different polarities via the separator in a plan view is protected by a tape or a resin film. Since the portion to which the current collector tab is attached becomes thicker as an electrode, it may cause an internal short circuit when stress is applied from the outside. Since the risk increases when the number of current collecting tabs is increased, it is preferable to attach a protective tape or the like so as to be 50 to 100% of the overlapping portion in order to reduce the risk.

[Positive electrode]
The positive electrode according to the non-aqueous electrolyte secondary battery of the present invention has a structure in which, for example, a positive electrode mixture layer containing a positive electrode active material, a conductive auxiliary agent, a binder, etc. is provided on one or both sides of a 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 , 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 of the above structural formulas, 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 M, y. Is the same as above) is particularly preferable.

<Binder>
As the binder used for the positive electrode, either a thermoplastic resin or 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), or ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methacryl One or more kinds such as a methyl acid copolymer and a Na ion cross-linked product of these copolymers can be used.

<Conductive aid>
The conductive auxiliary agent used for the positive electrode may be one that is chemically stable in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black and ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fiber and metal fiber; aluminum. Metal powders such as powder; carbon fluoride; zinc oxide; conductive whisker composed of potassium titanate and the like; conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives, etc. It may be used alone or in combination of two or more. Among these, graphite having high conductivity and carbon black having excellent liquid absorption are preferable. Further, the form of the conductive auxiliary agent is not limited to the primary particles, and those in the form of aggregates such as secondary aggregates and chain structures can also be used. Such an aggregate is easier to handle and has better productivity.

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

<Manufacturing method of positive electrode>
For the positive electrode, for example, a paste-like or slurry-like positive electrode mixture-containing composition in which the above-mentioned positive electrode active material, conductive auxiliary agent, and binder are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared. (However, the binder may be dissolved in a solvent.), This can be applied to one or both sides of the current collector, dried, and then subjected to a calendering treatment if necessary. .. The method for manufacturing the positive electrode is not limited to the above method, and other manufacturing methods can also be used.

<Positive electrode mixture layer>
In the positive electrode mixture layer, the total amount of the positive electrode active material is preferably 92 to 95% by mass, the amount of the conductive auxiliary agent is 3 to 6% by mass, and the amount of the binder is preferably 3 to 6% by mass. Further, 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 made thin, the maximum distance that lithium ions move during charging / discharging can be shortened, so that the internal resistance can be suppressed 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 a 300~2000cm ^2, and particularly preferably 500~1600cm ^2. This is because when the electrode area is smaller than 300 cm ^{2, the} capacitance becomes lower due to the balance with the electrode thickness described above, and the current value flowing also becomes smaller, so that the effect of increasing the current collecting tab becomes too small. This is because when 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 thickness and the capacity of the positive electrode mixture layer described above, and it becomes difficult to achieve both the energy density and the energy density.

The value obtained by dividing the battery capacity by the total area of the positive electrode mixture layer described above (referred to as “current density” in the present specification) is preferably 2.0 to 3.5. If the current density is less than 2, the energy density becomes too low, and if it is larger than 3.5, the polarization resistance at the time of high load charging / discharging becomes large, and the deterioration of the active material tends to proceed.

[Negative electrode]
The negative electrode according to the non-aqueous electrolyte secondary battery of the present invention has a structure having, for example, a negative electrode mixture layer containing a negative electrode active material, a binder and, if necessary, a conductive auxiliary agent, on one side or both sides of the 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 a conventionally known non-aqueous electrolyte secondary battery, that is, a material capable of storing and releasing lithium ions. For example, carbon-based materials capable of storing and releasing lithium ions, such as graphite, thermally decomposed carbons, cokes, glassy carbons, calcined bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One or a mixture of two or more 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 their alloys, lithium such as lithium-containing nitrides or lithium-containing oxides. 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 them, as the negative electrode active material, a mixture of graphite and a material represented by SiO _x (0.5 ≦ x ≦ 1.5) containing silicon and oxygen as constituent elements is preferable.

SiO _x may contain a microcrystalline or amorphous phase of Si, in which case the atomic ratio of Si to O is a ratio including the microcrystalline or amorphous phase of Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and the amorphous SiO ₂ is dispersed therein. It suffices that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 together with the Si. For example, in the case of a material in which Si is dispersed in an amorphous SiO ₂ matrix and the molar ratio of SiO ₂ and Si is 1: 1, x = 1, so the structural formula is expressed as SiO. Amorphous metal. 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 is observed. Can be confirmed.

The SiO _x is preferably a composite composite with a carbon material, and for example, it is desirable that the surface of the SiO _x is coated with a carbon material. Normally, SiO _x has poor conductivity, so when using this as a negative electrode active material, a conductive material (conductive aid) is used from the viewpoint of ensuring good battery characteristics, and SiO _x and conductivity in the negative electrode are used. It is necessary to form an excellent conductive network by improving mixing and dispersion with the 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 Is formed in.

<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 their variants; polyvinyl chloride, polyvinylpyrrolidone (PVP), and the like. Thermoplastic resins such as polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyamide and their variants; polyimide; ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber ( Examples thereof include polymers having rubber-like elasticity such as SBR), butadiene rubber, polybutadiene, fluororubber, and polyethylene oxide; and variants thereof; and one or more of these can be used.

<Conductive aid>
A conductive material may be further added to the negative electrode mixture layer as a conductive auxiliary agent. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery, and is, for example, carbon black (thermal black, furnace black, channel black, ketjen black, acetylene black, etc.), carbon. One or more materials such as fibers, metal powders (powder of copper, nickel, aluminum, silver, etc.), metal fibers, polyphenylene derivatives (described in JP-A-59-20971) may be used. 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 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. When the thickness of the entire negative electrode of this negative electrode current collector 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 secure mechanical strength. Is desirable.

<Manufacturing method of negative electrode>
For the negative electrode, for example, a paste-like or slurry-like negative electrode mixture-containing composition in which the above-mentioned negative electrode active material and binder and, if necessary, a conductive auxiliary agent are dispersed in a solvent such as NMP or water is prepared. , This can be applied to one or both sides of the current collector, dried, and then subjected to a calendering treatment if necessary. The method for manufacturing the negative electrode is not limited to the above-mentioned manufacturing method, and other manufacturing methods can be used for manufacturing the negative electrode.

<Negative electrode mixture layer>
In the negative electrode mixture layer, the total amount of the negative electrode active material is preferably 80 to 99% by mass, and the amount of the binder is preferably 1 to 20% by mass. When a conductive material is separately used as the conductive auxiliary agent, these conductive materials in the negative electrode mixture layer are used within a range in which the total amount of the negative electrode active material and the amount of the binder satisfy the above-mentioned suitable values. Is preferable.

In order to improve the discharge characteristics under a high load, the thickness of the negative electrode mixture layer is preferably 20 to 70 μm per side. This is because if the negative electrode mixture layer is made thin, the maximum distance that lithium ions move during charging / discharging can be shortened, so that the internal resistance can be suppressed 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, so that the negative electrode mixture layer can be easily thinned.

[Non-aqueous electrolyte]
As the non-aqueous electrolyte according to the non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent can be used.

The lithium salt used in the non-aqueous electrolytic solution is not particularly limited as long as it dissociates in a solvent to form lithium ions and does not easily cause side reactions such as decomposition in the 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 [Here, Rf is a fluoroalkyl group] and other organic lithium salts; Can be used.

The concentration of this lithium salt in the non-aqueous electrolytic solution 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 electrolytic solution is not particularly limited as long as it dissolves the above lithium salt and does not cause a side reaction such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate and 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, diglime, triglime, tetraglime; cyclic ethers such as dioxane, tetrahydrofuran, 2-methyltetrax; nitriles such as acetonitrile, propionitrile, methoxypropionitrile; ethylene Sulfurous acid esters such as glycolsulfite; and the like; these can also be used by mixing two or more kinds. In order to obtain a battery having better characteristics, it is desirable to use it in a combination capable of obtaining high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

[Separator]
The separator according to the non-aqueous electrolyte secondary battery has a property of closing its pores (that is, a shutdown function) at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower). It is preferable that a separator used in a normal non-aqueous electrolyte secondary battery or the like, for example, a microporous film made of polyolefin such as polyethylene (PE) or polypropylene (PP) can be used. The microporous membrane constituting the separator may be, for example, one using only PE or one using only PP, or a laminate of a microporous membrane made of PE and a microporous membrane made of PP. 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. In the past, since remarkable heat generation occurs due to current concentration on the positive electrode current collector tab portion, there is concern about an internal short circuit due to heat shrinkage of the separator at that location, and heat shrinkage 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, a thinner separator than before can be used, and it is possible to further contribute to the improvement of the volumetric energy density.

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

Separators for non-aqueous electrolyte secondary batteries include a porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower, 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. It is preferable to use a laminated separator having a porous layer (II) mainly containing. Here, the "melting point" means the melting temperature measured by a differential scanning calorimeter (DSC) according to the provisions of JIS K 7121. In addition, "does not melt at a temperature of 150 ° C. or lower" means that the melting temperature measured using a DSC exceeds 150 ° C. according to the provisions of JIS K 7121, and the temperature is 150 ° C. or lower when measuring the melting temperature. It means that it does not show melting behavior at the temperature of. Further, "heat resistant temperature of 150 ° C. or higher" means that no deformation such as softening is observed at at least 150 ° C.

The porous layer (I) related to the laminated separator is mainly for ensuring a shutdown function, and the non-aqueous electrolyte secondary battery is a resin which is a main component of the porous layer (I). When the temperature reaches the melting point or higher, the resin related to the porous layer (I) melts and closes the pores of the separator, 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-mentioned non-aqueous electrolyte secondary battery and a non-woven fabric. Examples thereof include those obtained by applying a dispersion liquid containing PE particles to a substrate such as, and drying the mixture. Here, among all the constituents of the porous layer (I), the volume of the resin having a melting point of 140 ° C. or lower as a main component is 50% by volume or more, 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) related to the laminated 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 non-aqueous electrolyte secondary battery rises. The function is ensured 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 temperature of the battery becomes high, even if the porous layer (I) shrinks, the porous layer (II) that does not easily shrink can directly cause the positive and negative electrodes to occur when the separator is thermally shrunk. It is possible to prevent a short circuit due to contact with. Further, since the heat-resistant porous layer (II) acts as a skeleton of the separator, the heat shrinkage of the porous layer (I), that is, the heat shrinkage 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 (for example, the above-mentioned PP battery) formed of a resin that does not melt at a temperature of 150 ° C. or lower. (Microporous film for use) is laminated on the porous layer (I), or a dispersion liquid 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. Examples thereof include a coating laminated type form in which a porous layer (II) is formed on the surface of the layer (I).

As a resin that does not melt at a temperature of 150 ° C. or lower, PP; crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensation. Various cross-linked polymer fine particles such as those; polysulfone; polyether sulfone; polyphenylene sulfide; polytetrafluoroethylene; polyacrylonitrile; aramid; polyacetal; and the like can be mentioned.

When resin particles that do not melt at a temperature of 150 ° C. or lower are used, the particle size thereof is preferably 0.01 μm or more, more preferably 0.1 μm or more, and more preferably 0.1 μm or more, in terms of average particle size. It is preferably 10 μm or less, and more preferably 2 μm or less. The average particle size of the various particles referred to in the present specification is, for example, an average particle measured by dispersing these particles in a medium that does not dissolve the particles using a laser scattering particle size distribution meter "LA-920" manufactured by HORIBA, Ltd. The diameter is D50%.

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 liquid containing an inorganic filler having a heat resistant temperature of 150 ° C. or higher is applied to the porous layer (I). , A coated laminated type form which is dried to form a porous layer (II).

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 with little redox in the operating voltage range of the battery. Anything may be used, but fine particles are preferable from the viewpoint of dispersion and the like, 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 desired values. Therefore, it is easy to accurately control the porosity of the porous layer (II). 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 of them 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 the above-mentioned resin that does not melt at a temperature of 150 ° C. or lower.

The shape of the inorganic filler having a heat resistant temperature of 150 ° C. or higher related to the porous layer (II) is not particularly limited, and is substantially spherical (including true sphere), substantially ellipsoidal (including ellipsoidal), and plate. Various shapes such as shapes can be used.

Further, the average particle size 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 permeability of ions decreases if it is too small. It is more preferably 5 μm or more. Further, if the inorganic filler having a heat resistant temperature of 150 ° C. or higher is too large, the electrical characteristics are likely to deteriorate. Therefore, the average particle size thereof is preferably 5 μm or less, 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), and thus these porous layers. 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 lower and an inorganic filler having a heat resistant temperature of 150 ° C. or higher, it is the amount. If both are included, the total amount of them. The same applies to the amounts 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 in the porous layer (II). ] Is 50% by volume or more, preferably 70% by volume or more, more preferably 80% by volume or more, and 90% by volume or more in the total volume of the constituent components of the porous layer (II). It is more preferable to have. By setting the heat-resistant material in the porous layer (II) to a high content as described above, it is possible to satisfactorily suppress the heat shrinkage of the entire separator even when the temperature of the non-aqueous electrolyte secondary battery becomes high. Therefore, the occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode can be suppressed more satisfactorily.

As will be described later, since it is preferable that the porous layer (II) also contains an organic binder, 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 The amount is preferably 99.5% by volume or less based on the total volume of the constituent components of the porous layer (II).

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 is bonded to the porous layer (II), or the porous layer (II) and the porous layer (I) are combined. It is preferable to include an organic binder for integration and the like. Examples of the organic binder include ethylene-vinyl acetate copolymer (EVA, which has a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymer such as ethylene-ethylacrylate copolymer, and fluorine-based binder. Examples thereof include rubber, SBR, CMC, hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), crosslinked acrylic resin, polyurethane, epoxy resin, etc., but in particular, at 150 ° C. or higher. A heat-resistant binder having a heat-resistant temperature is preferably used. As the organic binder, one of the above-mentioned examples may be used alone, or two or more of them may be used in combination.

Among the above-exemplified organic binders, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. For such highly flexible organic binders, Mitsui DuPont Polychemical's EVA "Evaflex Series", Nippon Unicar's EVA, and Mitsui DuPont Polychemical's ethylene-acrylic acid copolymer "Evaflex-EEA Series" , Nippon Unicar's EEA, Daikin Industries' fluororubber "Daiel Latex Series", JSR's SBR "TRD-2001", Nippon Zeon's SBR "BM-400B", etc.

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 the solvent of the composition for forming the porous layer (II) described later.

The coating-laminated separator is, for example, a composition for forming a porous layer (II) (liquid such as a slurry) containing resin particles that do not melt at a temperature of 150 ° C. or lower and an inorganic filler having a heat resistant temperature of 150 ° C. or higher. The composition, etc.) is applied to the surface of a membrane (microporous membrane, non-woven fabric, etc.) for forming the porous layer (I), and dried 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 if necessary, an organic binder or the like. Was dispersed in a solvent (including a dispersion medium; the same applies hereinafter). The organic binder can also be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) can uniformly disperse resin particles and inorganic fillers that do not melt at a temperature of 150 ° C. or lower, and can uniformly dissolve or disperse an organic binder. However, general 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. Alcohols (ethylene glycol, propylene glycol, etc.), various propylene oxide-based glycol ethers such as monomethyl acetate, and the like may be appropriately added to these solvents for the purpose of controlling the interfacial tension. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent, and alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added at this time as well. Interfacial tension can also be controlled.

The composition for forming the porous layer (II) has a solid content of 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 or the like. It is preferably ~ 80% by mass.

In the laminated separator, the porous layer (I) and the porous layer (II) do not have to be one layer each, and a plurality of layers may be contained in the separator. For example, the porous layer (I) may be arranged on both sides of the porous layer (II), or the porous layer (II) may be arranged on both sides of the porous layer (I). However, increasing the number of layers may increase the thickness of the separator, resulting in an increase in the internal resistance of the battery and a decrease in energy density. Therefore, it is not preferable to increase the number of layers too much, and the laminated separator is used. 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 by the present invention, but when the laminated separator is used, the effect of suppressing heat shrinkage is very high, so that the thickness of the separator should be 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 overall 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 suppressed low.

The porosity of the entire separator is preferably 30% or more in a dry state in order to secure the retention amount of the electrolytic solution and improve the ion permeability. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing an internal short circuit, the porosity of the separator 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 using the following formula (1) from the thickness of the separator, the mass per area, and the density of the constituent components.

P = {1-m / (Σaiρi × t)} × 100 (1)

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

In the case of the laminated separator, in the formula (1), m is the mass (g / cm ² ) per unit area of the porous layer (I), and t is the thickness of the porous layer (I) (I). By setting cm), the porosity of the porous layer (I): P (%) can also be obtained using the above 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 type separator, in the above formula (1), m is the mass (g / cm ² ) per unit area of the porous layer (II), and t is the thickness of the porous layer (II) (II). By setting cm), the porosity: P (%) of the porous layer (II) can also be obtained by using the above 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, and for example, the piercing strength is preferably 3N or more. For example, when SiO _x, which has a large volume change due to charging and discharging, is used as the negative electrode active material, the expansion and contraction of the entire negative electrode causes mechanical damage to the facing separators due to repeated charging and discharging. When the piercing strength of the separator is 3N or more, good mechanical strength can be ensured and the mechanical damage to the separator can be mitigated.

Examples of the separator having a piercing strength of 3 N or more include the above-mentioned laminated type separator. In particular, an inorganic filler having a heat resistant temperature of 150 ° C. or higher is formed on a 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 the above is laminated is preferable. It is considered that this is because the mechanical strength of the inorganic filler is high, so that the mechanical strength of the porous layer (I) can be supplemented and the mechanical strength of the entire separator can be increased.

The piercing strength can be measured by the following method. A separator is fixed on a plate with a hole with a diameter of 2 inches so as not to wrinkle or bend, and a hemispherical metal pin with a tip diameter of 1.0 mm is lowered onto the measurement sample at a speed of 120 mm / min. , Measure the force when the separator is punctured 5 times. Then, the average value is obtained for three measurements excluding the maximum value and the minimum value among the five measurement values, and this is used as the piercing strength of the separator.

The positive electrode, the negative electrode, and the separator are formed as an electrode body in which a separator is interposed between the positive electrode and the negative electrode and is wound in a spiral shape, and the cross section is flattened. Used for the next battery.

In the electrode body, the laminated separator, particularly the porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower, and the porous layer (II) mainly containing an inorganic filler having a heat resistant temperature of 150 ° C. or higher. ) Is used, it is preferable to arrange the porous layer (II) so as to face at least the positive electrode. In this case, since the porous layer (II), which mainly contains an inorganic filler having a heat resistant temperature of 150 ° C. or higher and has more excellent oxidation resistance, faces the positive electrode, the oxidation of the separator by the positive electrode can be suppressed more satisfactorily. It is also possible to further improve the storage characteristics and charge / discharge cycle characteristics of the battery at high temperatures. Further, it is possible to add additives such as vinylene carbonate and cyclohexylbenzene to the non-aqueous electrolyte to further enhance various characteristics of the battery, but when such additives are added, a film is formed on the positive electrode side. This may clog the pores of the separator and cause deterioration of battery characteristics. Therefore, by facing the relatively porous porous layer (II) to the positive electrode, the effect of suppressing clogging of the pores can be expected.

The non-aqueous electrolyte secondary battery of the present invention can be used with a charging upper limit voltage of about 4.2 V as in the conventional non-aqueous electrolyte secondary battery, but the charging upper limit voltage is higher than this 4 It is also possible to set it to .3 V or higher and use it, so that it is possible to stably exhibit excellent characteristics even if it is used repeatedly for a long period of time while increasing the capacity. The upper limit voltage for charging the non-aqueous electrolyte secondary battery is preferably 4.7 V or less.

The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as the 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, devices that require high capacity for a limited volume, such as mobile devices, small devices, and multiple cells are combined in series. It is particularly effective when the volumetric energy density is 350 to 800 Wh / L, such as in robot applications. Further, the non-aqueous electrolyte secondary battery of the present invention has good characteristics when the battery capacity is 1.0 to 5.0 Ah when measured under the conditions (described in Examples) described later, and particularly 1.5 to 4 It shows optimum characteristics in the range of 0.0 Ah. In applications such as robots, it is not necessary to increase the absolute battery capacity in consideration of its use, so the battery of the present invention fits well.

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 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 of 8: 2 (mass ratio) and 10 parts by mass of PVDF which is a binder. 20 parts by mass of NMP solution contained at a concentration of%, 1 part by mass of artificial graphite and 1 part by mass of Ketjen black, which are conductive aids, are kneaded using a twin-screw kneader, and further NMP is added to adjust the viscosity. Then, a paste containing a positive electrode mixture was prepared.

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

<Manufacturing of negative electrode>
A composite in which the SiO surface of the negative electrode active material having an average particle diameter D50% of 8 μm is coated with a carbon material (the amount of carbon material in the composite is 10% by mass) and graphite having an average particle diameter D50% of 16 μm. A mixture of 97.5 parts by mass, a binder SBR: 1.5 parts by mass, and a thickener in which the amount of the composite in which the SiO surface is coated with a carbon material is 3.75% by mass. Water was added to and mixed with 1 part by mass of CMC (CMC) to prepare a negative electrode mixture-containing paste.

As shown in FIGS. 3 and 4, the negative electrode mixture-containing paste is applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum dried at 120 ° C. for 12 hours to obtain the copper foil. Negative electrode mixture layers were formed on both sides and a part of one side. After that, a pressing process is performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel negative electrode current collecting tab is welded to the exposed portion of the copper foil as shown in FIGS. 3 and 4 to lengthen the negative electrode mixture layer. 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 of 45 μm per side.

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

<Making a separator>
To 5 kg of plate-shaped boehmite (average particle size 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) were added to form an internal volume of 20 L. A dispersion was prepared by crushing for 10 hours with a ball mill having a number of turns of 40 times / minute. A part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM). As a result, the shape of boehmite was almost plate-like. The average particle size of 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 resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added, and the mixture is stirred with a three-one motor for 3 hours to make uniform porous. A slurry for forming the layer (II) (solid content ratio: 50% by mass) was prepared.

Corona discharge treatment (discharge amount 40 W / min / m2) on one side of a microporous film made of PE (thickness 10 μm, porosity 40%, average pore diameter 0.08 μm, melting point 135 ° C. of PE) which is a porous layer (I). ) Is applied, the slurry for forming the porous layer (II) is applied to the treated surface by a microgravure coater, and the porous layer (II) having a thickness of 2 μm is formed on one surface on the separator and laminated. A mold separator was prepared.

<Battery assembly>
As shown in FIG. 5, the strip-shaped positive electrode is superposed on the strip-shaped negative electrode via the laminated separator (porosity: 42%), wound in a spiral shape, and then added so as to have a flat shape. It was pressed into an electrode body, and this electrode body was 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 the side view from the wide surface as shown in FIG. At this time, the wide surface dimensions of the electrode body were 50 mm in the width direction (perpendicular to the winding axis direction) and 58 mm in the height direction (parallel to the winding axis direction).

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

The non-aqueous electrolyte secondary battery 100 has an outer can 111 and a lid plate 121, which also serve as positive electrode terminals. The outer can 111 includes a pair of side surface portions 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 rises. The lid 121 is inserted into the opening of the outer can 111, and by welding the joint between the two, the opening of the outer can 111 is sealed and the inside of the battery is sealed. The lid 121 is provided with a non-aqueous electrolyte injection port, and the non-aqueous electrolyte injection port is welded and sealed by, for example, laser welding, with the sealing member 122 inserted therein. The 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 welded directly to the lid 121 so that the outer can 111 and the lid 121 function as positive electrode terminals, and the negative electrode current collecting tab is welded to the lead plate inside the battery. The terminal 123 functions as a negative electrode terminal by conducting the terminal 123 with the terminal 123 via the lead plate.

Example 2
A non-aqueous 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 band-shaped positive electrode and the band-shaped 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.

Then, the non-aqueous electrolyte secondary battery is the same as in Example 1 except that the flat electrode body is inserted into a square can made of an aluminum alloy having an outer dimension of 4.8 mm in thickness, 38 mm in width, and 60 mm in height. Was produced.

Example 4
A band-shaped 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 band-shaped positive electrode and the band-shaped 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.

Then, the non-aqueous electrolyte secondary battery is the same as in Example 1 except that the flat electrode body is inserted into a square can made of an aluminum alloy having an outer dimension of 4.8 mm in thickness, 78 mm in width, and 60 mm in height. Was produced.

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

Comparative Example 2
A band-shaped 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 the positive electrode was used, and a microporous membrane made of PE (thickness 20 μm) was used. A non-aqueous electrolyte secondary battery was produced in the same manner as in the above.

Comparative Example 3
The same band-shaped positive electrode, band-shaped negative electrode and separator as those used in Example 1 are overlapped, the position of the positive electrode winding start is changed from 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 by arranging the positive electrode current collecting tabs 213b on the innermost peripheral side of the body in the arrangement shown in FIG.

Then, a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the flat electrode body 203 was used.

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

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

<Battery capacity>
Each of the batteries of Examples and Comparative Examples was once completely discharged by discharging a constant current (hereinafter referred to as CC) to 2.75 V at a 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 charge current value was 1 C, and the charge termination current value was 0.05 C. Subsequently, CC discharge was performed for each battery up to 2.75 V at a current value of 0.2 C, and the discharge capacity at that time was measured. The capacity at this time was taken as the battery capacity.

<Discharge load characteristics>
Each of the batteries of Examples and Comparative Examples was once completely discharged by CC discharging to 2.75 V at a current value of 1 C. Next, each battery was charged with CCCV up to 4.35V. The CC charge current value was 1 C, and the charge termination current value was 0.05 C. Subsequently, CC discharge was performed for each battery up to 2.75 V at a current value of 0.2 C, and the discharge capacity at that time was measured.

Then, each battery was charged with CCCV again under the same conditions, CC-discharged to 2.75 V with a current value of 10 C, and the discharge capacity at that time and the surface temperature of the battery were evaluated.

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

<1 kHz AC resistance [impedance (Imp.)]>
The 1 kHz AC resistance of each non-aqueous electrolyte secondary battery of Examples and Comparative Examples is CC discharged to 2.75 V at a current value of 1 C, then CCC V charged to 4.35 V, and then resistance measurement manufactured by HIOKI. It was measured at 25 ° C. using the machine "HiTESTER".

<Measurement of battery thickness>
The thickness of each non-aqueous electrolyte secondary battery of Examples and Comparative Examples was flattened at the center of the wide surface of the outer can and the wide surface of the outer can using a thickness gauge (measurement part φ10 mm flat circle) manufactured by Mitutoyo Co., Ltd. The measurement was performed at the location corresponding to the current collection tab of the electrode body of the 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>
Each of the non-aqueous electrolyte secondary batteries of Examples and Comparative Examples was once completely discharged by CC discharging to 2.75 V at a current value of 1 C. Next, each battery was charged with CCCV up to 4.35V. The CC charge current value was 1 C, and the charge termination current value was 0.05 C. Subsequently, CC discharge was performed for each battery up to 2.75 V at a current value of 5 C, and the initial discharge capacity at that time was determined. After that, the charge / discharge condition was set to one cycle, and the discharge capacity of each battery when 500 cycles of charge / discharge was repeated was determined. In Table 3, for each battery, the value obtained by dividing the discharge capacity after 500 cycles by the initial discharge capacity is shown as a percentage (capacity retention rate).

As in Examples 1 to 4, the non-aqueous electrolyte secondary battery has a flat electrode body, 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 surface side. Since the impedance is low, the 10C / 0.2C discharge capacity ratio is high, and the temperature rise on the battery surface is suppressed. Furthermore, the difference between the thickness of the central part of the wide surface of the battery and the maximum thickness is small, and the thickness unevenness of the wide surface is small, so that the distortion of the electrode body caused by the bias of the voids in the electrode body during charging and discharging is small, so that the cycle capacity is high. A maintenance rate was obtained.

The battery of Comparative Example 1 having a cylindrical electrode body had poor heat dissipation as compared with the battery of Example 1 having a flat electrode body, and the temperature rose during high-load discharge. Furthermore, the poor heat dissipation has adversely affected 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 had a small capacity when discharged under a high load because of its high impedance. The batteries of Comparative Examples 3 and 4 having the electrode bodies arranged so that the two positive electrode current collecting tabs overlap when viewed from the side had a low capacity retention rate at the time of evaluating the charge / discharge cycle characteristics. In the batteries of Comparative Examples 3 and 4, since the wide surface of the flat electrode body had uneven thickness, it is considered that the charge / discharge capacity loss occurred while the charge / discharge cycle was repeated, and the capacity retention rate became low.

The present invention can be implemented in a form other than the above as long as it does not deviate from the gist thereof. 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 shall be construed in preference to the description of the appended claims over the description of the specification, and all modifications within the scope of the claims shall be within the scope of the claims. included.

The present invention applies to non-aqueous electrolyte secondary batteries.

1 Positive electrode 13a, 13b Positive electrode current collector tab 2 Negative electrode 3 Flat electrode body 30 Wide surface 100 Non-aqueous electrolyte secondary battery

Claims (8)

A flat electrode body with a pair of wide surfaces is housed inside the exterior.
In the flat electrode body, a long positive electrode and a long negative electrode are laminated via a separator and wound in a spiral shape.
The positive electrode and the negative electrode have a positive electrode current collecting tab and a negative electrode current collecting tab, respectively.
The positive electrode has two current collecting tabs.
The separator has a thickness of 20 μm or less.
The positive electrode current collecting tab and the negative electrode current collecting tab are arranged so as to project in the same direction in the winding axis direction of the electrode body and not to overlap when the electrode body is viewed from the wide surface side. A non-aqueous electrolyte secondary battery characterized by being present. The non-aqueous 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 a constant current up to 2.75V with a current value of 1C, it is once completely discharged. Next, constant current and constant voltage charging is performed up to 4.35V. The current value of constant current charging is 1C, and the charging termination current value is 0.05C. Subsequently, a constant current discharge is performed up to 2.75 V with a current value of 0.2 C, and the discharge capacity at that time is defined as the battery capacity. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the wide surface has a length of 30 to 80 mm in a direction perpendicular to the winding axis direction. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the separator has a thickness of less than 14 μm. The separator has a porous layer (I) mainly composed of a resin having a melting point of 140 ° C. or lower, and
Porous layer (II) mainly containing 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.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, which is a laminated separator having the above. The positive electrode has a positive electrode mixture layer on one side or both sides of a positive electrode current collector.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the thickness of the positive electrode mixture layer is 20 to 70 μm on one side. The positive electrode has a positive electrode mixture layer on one side or both sides of a positive electrode current collector.
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the total area of the positive electrode mixture layer on the positive electrode current collector is 300 to 2000 cm ² . The non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the positive electrode current collecting tab and the negative electrode current collecting tab have a cross-sectional area of 0.15 to 1.0 mm ² .

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