WO2017051514A1

WO2017051514A1 - Cylindrical nonaqueous electrolyte secondary battery

Info

Publication number: WO2017051514A1
Application number: PCT/JP2016/004173
Authority: WO
Inventors: 柴野　靖幸; 翔太矢冨
Original assignee: 三洋電機株式会社
Priority date: 2015-09-25
Filing date: 2016-09-14
Publication date: 2017-03-30

Abstract

This cylindrical nonaqueous electrolyte secondary battery comprises: an electrode body which is obtained by winding a positive electrode plate and a negative electrode plate together, with a separator being interposed therebetween; an electrolyte solution; a center pin which is inserted into a hollow part that is formed in a position corresponding to the winding axis of the electrode body; and a bottomed cylindrical outer package can which contains the electrode body and the electrolyte solution. The separator comprises a base layer and a heat-resistant layer that is formed on at least one surface of the base layer. The base layer contains a polyolefin as a main component; and the heat-resistant layer contains a heat-resistant polymer as a main component. The maximum height Rz of the surface of the base layer, said surface serving as the base for the heat-resistant layer, is from 0.1 μm to 3 μm (inclusive).

Description

Cylindrical non-aqueous electrolyte secondary battery

The present invention relates to a cylindrical non-aqueous electrolyte secondary battery, and more particularly to a cylindrical non-aqueous electrolyte secondary battery exhibiting high safety by improving a separator.

A non-aqueous electrolyte secondary battery having high energy density is used as a power source for mobile devices such as notebook computers and mobile phones. In recent years, non-aqueous electrolyte secondary batteries have become widespread as power sources for electric tools, assist bicycles, and electric vehicles, and a further increase in capacity is required. In particular, a cylindrical nonaqueous electrolyte secondary battery is often used in a harsh environment as an assembled battery in which a plurality of batteries are connected in series or in parallel. For this reason, the cylindrical nonaqueous electrolyte secondary battery is provided with various means for ensuring safety.

For example, in a cylindrical non-aqueous electrolyte secondary battery, a cylindrical center pin is inserted into a hollow portion formed in a core portion of a wound electrode body. Many center pins are formed by bending a metal plate into a cylindrical shape. The center pin so formed has a slit formed on the side surface along the length direction. Patent Documents 1 to 3 are cited as prior art documents disclosing a cylindrical non-aqueous electrolyte secondary battery having a center pin.

In Patent Document 1, a center pin is used to short-circuit the inner periphery of the electrode body when the electrode body is crushed. When the electrode body is crushed, the end portion of the slit of the center pin is deformed outward, and the end portion breaks the inner peripheral portion of the electrode body to promote internal short circuit. Thereby, a short circuit current concentrates on the inner peripheral side of an electrode body, and the temperature rise of the positive electrode active material layer by a short circuit current is suppressed.

In Patent Documents 2 and 3, a center pin is used to prevent deformation of the electrode body due to charge / discharge. The center pin is not only formed by bending a metal plate into a cylindrical shape, but also in the vicinity of the slit so that the end face of the slit is oriented inside the cylindrical portion of the center pin. Thereby, when the electrode body is crushed, the end surface of the slit of the center pin is deformed toward the inside of the center pin, so that an internal short circuit due to the slit of the center pin is prevented.

Non-aqueous electrolyte secondary batteries generally use a polyolefin microporous membrane as a separator. A separator containing a polyolefin having a low melting point exhibits a shutdown function that suppresses movement of lithium ions between the positive and negative electrodes when the battery temperature rises. This shutdown function utilizes the phenomenon that the polyolefin softens with increasing temperature and closes the opening of the separator. In order to effectively exhibit the shutdown function, polyethylene is preferably used as the polyolefin.

However, when the battery temperature rises above the shutdown temperature of the separator, the separator shrinks or melts, and the insulation between the positive and negative electrodes may be impaired. Therefore, a method of arranging a heat-resistant layer between the positive electrode and the negative electrode has been proposed. The heat resistant layer is formed on the surface of any of the positive electrode plate, the negative electrode plate, and the separator. The heat-resistant layer can ensure insulation between the positive and negative electrodes even when the battery temperature rises abnormally. The heat-resistant layer formed on the separator can suppress the shrinkage of the separator. Patent Documents 4 to 7 are cited as prior art documents disclosing forming a heat-resistant layer on a separator.

Japanese Patent Laid-Open No. 08-255631 Japanese Patent Laid-Open No. 2003-092148 JP 2003-229177 A JP 2006-032246 A Japanese Patent Laid-Open No. 2007-299612 JP 2010-021033 A JP 2013-105578 A

The technique described in Patent Document 1 may not be effective for a high-capacity cylindrical nonaqueous electrolyte secondary battery, and an internal short circuit caused by the center pin when the electrode body is crushed is It is preferably prevented. According to the techniques described in Patent Documents 2 and 3, an internal short circuit caused by the slit of the center pin is suppressed. However, regardless of the presence or absence of slits, when the battery is crushed and the electrode body is crushed, the presence of a center pin applies a large force locally to the electrode plate and separator, so the separator with insufficient mechanical strength breaks. There is a risk.

The technology for forming a heat-resistant layer on the surface of the base material layer of the separator as in Patent Documents 4 to 7 is effective as a means for preventing an internal short circuit due to shrinkage or melting of the separator. However, this technique is not always effective as a means for ensuring safety when the electrode body is crushed in a crush test or the like. When the heat-resistant layer is formed on the surface of the base material layer of the separator, it is necessary to reduce the thickness of the base material layer by the thickness of the heat-resistant layer. Therefore, forming a heat-resistant layer on the surface of the separator may lead to a decrease in the mechanical strength of the separator.

The present invention has been made in view of the above, and ensures safety during a crushing test of a cylindrical non-aqueous electrolyte secondary battery having a separator having a heat-resistant layer formed on a substrate mainly composed of polyolefin. For the purpose.

In order to solve the above problems, a cylindrical nonaqueous electrolyte secondary battery according to one embodiment of the present invention includes an electrode body in which a positive electrode plate and a negative electrode plate are wound via a separator, a nonaqueous electrolyte, and an electrode body It has a center pin inserted into a hollow portion formed at a position corresponding to the winding shaft portion, and a bottomed cylindrical outer can that accommodates the electrode body and the nonaqueous electrolyte. The separator includes a base material layer containing polyolefin as a main component and a heat resistant layer formed on at least one surface of the base material layer and containing a heat-resistant polymer as a main component. The maximum height Rz of the surface of the base material layer that is the base of the heat-resistant layer is 0.1 μm or more and 3 μm or less.

According to the present invention, the breakage of the separator is suppressed when the cylindrical nonaqueous electrolyte secondary battery is crushed by the crush test or the like. Therefore, according to the present invention, the safety of the cylindrical nonaqueous electrolyte secondary battery can be enhanced.

FIG. 1 is a cross-sectional perspective view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a main part of a separator according to one embodiment of the present invention.

A cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described with reference to FIGS. In addition, this invention is not limited to the following embodiment, In the range which does not change the summary of this invention, it can change suitably and can implement.

The cylindrical nonaqueous electrolyte secondary battery 10 has an electrode body 14 and a nonaqueous electrolyte housed inside a bottomed cylindrical outer can 20. The inside of the cylindrical non-aqueous electrolyte secondary battery 10 is sealed by caulking and fixing the sealing body 21 to the opening of the outer can 20 via the gasket 19.

The electrode body 14 is produced by winding the positive electrode plate 12 and the negative electrode plate 13 through the separator 11. At this time, the hollow portion 15 is formed at a position corresponding to the winding shaft portion of the electrode body. A center pin 16 is inserted into the hollow portion 15. In order to facilitate the insertion of the center pin 16, it is preferable to form the hollow portion 15 so that the cross-sectional shape is a perfect circle.

In this embodiment, a center pin 16 formed by bending a plate-like member into a cylindrical shape is used, and a slit is formed on the side surface along the length direction. Further, the tip of the slit is bent inside the center pin 16. That is, the cross-sectional shape of the center pin 16 is a shape in which the C-shaped tip is bent inward, but is not limited thereto. Although a metal member processed into a pipe shape can be used for the center pin 16, it is preferable from the viewpoint of cost reduction to use the center pin 16 formed of a metal plate in a cylindrical shape as in this embodiment.

The material of the center pin 16 can be used without limitation as long as it has a strength that can ensure the shape of the hollow portion 15 of the electrode body 14 even when charging and discharging are repeated and corrosion resistance in the nonaqueous electrolyte. Examples of preferred materials for the center pin 16 include stainless steel, nickel, titanium, and iron. When iron is used, it is preferable to plate with nickel in order to ensure corrosion resistance in the non-aqueous electrolyte.

The separator 11 is comprised from the base material layer 11a and the heat-resistant layer 11b formed in the surface, as shown in FIG. It is sufficient that the heat-resistant layer 11b is formed on one surface of the base material layer 11a. In the present embodiment, the heat-resistant layer 11 b is formed only on the side of the separator 11 that faces the positive electrode plate 12. The heat-resistant layer 11b may be formed on the side of the separator 11 facing the negative electrode plate 13, or may be formed on both surfaces of the base material layer 11a.

The base material layer 11a is made of a microporous film containing polyolefin as a main component, and the polyolefin is preferably polyethylene, polypropylene, or a copolymer of ethylene and propylene. By using polyolefin as the base material layer 11a, when the battery temperature rises abnormally, the holes in the base material layer 11a are closed at a temperature of 120 to 150 ° C., and the current between the positive and negative electrodes is cut off. Thereby, since an electrode reaction stops, the rise in battery temperature can be suppressed. Polypropylene having a melting point exceeding 150 ° C. is preferably used together with polyethylene.

The base material layer 11a can contain other polymers together with polyolefin. By appropriately selecting another polymer, shrinkage of the base material layer 11a when the battery temperature rises can be prevented.

Other polymers include polystyrene, rubber-containing polystyrene, and styrene polymers such as acrylonitrile-styrene copolymers; polyesters such as polyethylene terephthalate; polyamides such as polyamide 6 and polyamide 12; acrylic polymers such as polymethyl methacrylate; cellulose derivatives; Examples are thermoplastic polymers such as thermoplastic elastomers.

The content of polyolefin in the base material layer 11a is preferably 40 to 100% by mass, more preferably 50 to 100% by mass. The thickness of the base material layer 11a is preferably 3 to 220 μm. The average pore diameter of the base material layer 11a is preferably 0.05 to 2 μm. The porosity of the base material layer 11a is preferably 25 to 80% by volume, more preferably 25 to 75% by volume. The puncture strength of the base material layer 11a is preferably 300 gf or more, more preferably 400 gf or more.

The heat-resistant layer 11b is mainly composed of a polymer having heat resistance. It is a necessary condition for the heat resistance that the melting point and heat shrinkage starting temperature of the polymer are higher than the melting point and heat shrinkage starting temperature of the base material layer 11a, respectively. As the main component of the heat-resistant layer 11b, a polymer having a melting point higher than 150 ° C. and lower than or equal to 350 ° C., more preferably higher than or equal to 170 ° C. and lower than or equal to 300 ° C. can be used.

Polyamides; polyamides, polyamide copolymers, and amide bond-containing polymers such as aramids; polymers of polyvinylidene fluoride (PVDF), vinylidene fluoride (VF) and propylene hexafluoride (HFP) Polymers and fluorine-containing polymers such as polytetrafluoroethylene (PTFE); Imido bond-containing polymers such as polyimide (PI), polyamideimide (PAI), and polyetherimide (PEI); polyethylene terephthalate (PET), polypropylene terephthalate ( PPT), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polyethylene naphthalate (PEN) And polyalkylene arylates such as polybutylene naphthalate (PBN); polyarylate (PAR); polymers having sulfonic groups such as polysulfone (PSF) and polyethersulfone (PES); polyphenylene ether (PPE); polycarbonate (PC); Examples include polyphenylene sulfide (PPS); aromatic polyetherketone polymers such as polyetherketone (PEK) and polyetheretherketone (PEEK); polyoxymethylene (POM); polyethernitrile (PEN).

Of the above polymers, amide bond-containing polymers, fluorine-containing polymers, and imide bond-containing polymers are preferable. In particular, aramid, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (VDF-HFP) copolymer, polyimide ( PI) and polyamideimide (PAI) are more preferable.

The above polymers can be used alone or in combination of two or more. The heat-resistant layer 11b can contain another polymer other than the heat-resistant polymer as the main component as long as the heat resistance is not impaired. It is preferable that content of the said other polymer is 10 mass% or less with respect to the mass of the heat-resistant layer 11b.

The heat-resistant layer 11b can contain an inorganic filler made of insulating inorganic particles in addition to the heat-resistant polymer as the main component. As the inorganic filler, inorganic oxides such as silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), magnesium oxide (MgO), and zirconium oxide (ZrO ₂ ) are preferable.

The thickness of the heat-resistant layer 11b can be selected from the range of 0.01 to 50 μm, preferably 0.1 to 20 μm, more preferably 0.5 to 10 μm. The average pore diameter of the heat-resistant layer 11b is preferably 0.05 to 2 μm. The porosity of the heat-resistant layer 11b is preferably 25 to 80% by volume, more preferably 25 to 75% by volume.

The heat-resistant layer 11b can be formed by applying a coating liquid containing a main component polymer on the base material layer 11a by a known coating method and drying it. As the coating liquid, a solution in which the main component polymer is dissolved in a solvent, or a dispersion liquid in which the main component polymer is dispersed in a dispersion medium can be used. Examples of the solvent or dispersion medium for the coating solution include alcohols such as methanol, ethanol, and ethylene glycol (such as C2-4 alkanol or C2-4 alkanediol); ketones such as acetone; ethers such as diethyl ether and tetrahydrofuran; dimethylformamide, and the like Nitriles such as acetonitrile; sulfoxides such as dimethyl sulfoxide; N-methyl-2-pyrrolidone (NMP) and the like. These solvents and dispersion media can be used alone or in combination of two or more.

The positive electrode plate 12 is composed of a positive electrode current collector and a positive electrode active material layer formed on the surface thereof. As the positive electrode current collector, for example, aluminum, an aluminum alloy, stainless steel, titanium, or a metal foil formed of a titanium alloy can be used. The thickness of the positive electrode current collector is, for example, 1 to 100 μm, preferably 5 to 70 μm, more preferably 10 to 50 μm.

The positive electrode active material layer can contain a binder and a conductive agent in addition to the positive electrode active material. As the positive electrode active material, any material that can electrochemically occlude and release lithium ions can be used without limitation. As the positive electrode active material, LiCoO ₂ , LiNiO ₂ , LiCo _x Ni _1-x O ₂ (0 <x <1), LiMn ₂ O ₄ , LiNi _0.4 Mn _1.6 O ₄ , LiCoPO ₄ , LiFePO ₄ , LiCoPO ₄ _{_{_{_{4-y F y (0 <}}}} y <1), LiFePO 4-z F z (0 <z <1), Li 4 Ti 5 O 12, Li 4 Fe 0.5 Ti 4.5 O 12, and Li ₄ Examples include lithium transition metal composite oxides such as Zn _0.5 Ti _4.5 O ₁₂ ; metal oxides such as V ₂ O ₅ and MnO ₂ ; sulfides such as TiS ₂ and LiFeS ₂ . These can be used alone or in combination of two or more. These may be used by adding at least one selected from the group consisting of Al, Ti, Mg, and Zr, or replacing the metal element.

Examples of the conductive agent include carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite such as natural graphite and artificial graphite; and conductive fiber such as carbon fiber and metal fiber. Is done. As the binder, polyvinylidene fluoride (PVDF), a modified product of polyvinylidene fluoride (PVDF), and a fluororesin such as polytetrafluoroethylene (PTFE); styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBR) ) And rubber particle binders such as polymers having acrylate units; and cellulose derivatives such as carboxymethylcellulose (CMC).

The thickness of the positive electrode active material layer is not particularly limited, but is, for example, 0.1 to 150 μm, preferably 1 to 100 μm, more preferably 10 to 90 μm.

The negative electrode plate 13 is composed of a negative electrode current collector and a negative electrode active material layer formed on the surface thereof. As the negative electrode current collector, for example, a metal foil formed of copper, a copper alloy, nickel, a nickel alloy, or stainless steel can be used. The thickness of the negative electrode current collector is, for example, 1 to 100 μm, preferably 2 to 50 μm, more preferably 3 to 30 μm.

The negative electrode active material layer can contain a binder and a conductive agent in addition to the negative electrode active material. As the negative electrode active material, any material capable of electrochemically occluding and releasing lithium ions can be used without limitation. Carbon materials such as graphite and carbon nanotubes as the negative electrode active material; metal materials containing at least one selected from the group consisting of Li, Al, Zn, Sn, In, Si, Ta, and Nb or oxides thereof; Li ₄ Lithium titanium oxide having a spinel structure such as Ti ₅ O ₁₂ , Li ₄ Fe _0.5 Ti _4.5 O ₁₂ , and Li ₄ Zn _0.5 Ti _4.5 O ₄ ; Sulfide such as TiS ₄ ; LiCo Examples include nitrides such as _2.6 O _0.4 N and Ta ₃ N ₅ . These can be used alone or in combination of two or more. A small amount of dissimilar metal may be added to the metal material, oxide, sulfide, and nitride. Among the exemplified negative electrode active materials, it is preferable to use a carbon material, Si, and an oxide thereof.

As the conductive agent and binder used for the negative electrode plate 13, those exemplified as the conductive agent and binder used for the positive electrode plate 12 can be used.

The thickness of the negative electrode active material layer is not particularly limited, but is, for example, 0.1 to 150 μm, preferably 1 to 120 μm, more preferably 10 to 100 μm.

Known methods can be used for forming the positive electrode active material layer and the negative electrode active material layer. For example, wet coating methods such as a die coating method and a gravure coating method, a sputtering method, a physical vapor deposition method, a chemical vapor deposition method, and a screen. The printing method is mentioned. Each of the positive electrode active material layer and the negative electrode active material layer may be formed only on one side of the current collector, or may be formed on both sides.

As the non-aqueous electrolyte, a solution obtained by dissolving a lithium salt as an electrolyte salt in a non-aqueous solvent can be used.

As the non-aqueous solvent, a cyclic carbonate, a chain carbonate, a cyclic carboxylic acid ester and a chain carboxylic acid ester can be used, and these are preferably used in a mixture of two or more. Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). In addition, a cyclic carbonate in which part of hydrogen is substituted with fluorine, such as fluoroethylene carbonate (FEC), can also be used. Examples of the chain carbonate include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propyl carbonate (MPC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (γ-BL) and γ-valerolactone (γ-VL). Examples of chain carboxylic acid esters include methyl pivalate, ethyl pivalate, methyl isobutyrate and methyl Pionate is exemplified.

LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ and Li ₂ B ₁₂ Cl ₁₂ are exemplified. Among these, LiPF ₆ is particularly preferable, and the concentration of the lithium salt in the nonaqueous electrolyte is preferably 0.5 to 2.0 mol / L. Other lithium salts such as LiBF ₄ may be mixed with LiPF ₆ .

An embodiment of the present invention will be described in more detail below using specific examples. The present invention is not limited to the following examples.

Example 1
(Preparation of separator)
As the base material layer 11a, a polyethylene microporous film having a thickness of 20 μm was used. This microporous membrane was produced by extruding molten polyethylene and forming it into a sheet shape, and stretching the obtained molded product in a biaxial direction. The base material layer 11a having a maximum surface height Rz of 0.1 μm was prepared by adjusting the conditions for stretching the melted polyethylene.

A polyamide as a heat-resistant polymer is dissolved in N-methyl-2-pyrrolidone (NMP) as a solvent, and 2 parts by mass of aluminum oxide (Al ₂ O ₃ , average particle diameter is 1 part by mass of polyamide) 0.013 μm) was added to the solvent to prepare a coating solution. The coating liquid was applied to one side of the base material layer 11a and dried to form a heat-resistant layer 11b having a thickness of 3.5 μm. In this way, the separator 11 according to Example 1 was produced.

The piercing strength of the base material layer 11a was 420 gf. The puncture strength was determined by applying a needle-like terminal with a tip of φ1 mm to the base material layer 11a applied with tension from both ends at 200 mm / min. And measured at a constant speed. The maximum load when the base material layer 11a broke was defined as the piercing strength.

(Preparation of positive electrode plate)
100 parts by mass of lithium nickel cobalt aluminum oxide represented by LiNi _0.82 Co _0.15 Al _0.03 O ₂ as a positive electrode active material, 1 part by mass of acetylene black as a conductive agent, and as a binder It mixed so that polyvinylidene fluoride (PVDF) might be 0.9 mass part. The mixture was put into N-methyl-2-pyrrolidone (NMP) as a dispersion medium and kneaded to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was intermittently applied to both surfaces of a strip-shaped aluminum foil having a thickness of 15 μm as a positive electrode current collector, and dried to form a positive electrode active material layer. The positive electrode active material layer was compressed to a predetermined thickness with a roll. The positive electrode lead 12a made of aluminum was ultrasonically welded to the exposed portion of the positive electrode current collector where the positive electrode active material layer was not formed. A positive electrode plate 12 was produced by applying a polyimide insulating tape so as to cover the positive electrode lead 12a.

(Preparation of negative electrode plate)
The scale-like graphite as the negative electrode active material is 100 parts by mass, the styrene-butadiene rubber (SBR) as the binder is 1 part by mass, and the sodium salt of carboxymethyl cellulose (CMC) as the thickener is 1 part by mass. Mixed. The mixture was put into water as a dispersion medium and kneaded to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was intermittently applied to both surfaces of a strip-shaped copper foil having a thickness of 10 μm as a negative electrode current collector, and dried at 110 ° C. for 30 minutes to form a negative electrode active material layer. The negative electrode active material layer was compressed to a predetermined thickness with a roll. The negative electrode lead 13b made of nickel was resistance-welded to the exposed portion of the negative electrode current collector on which the negative electrode active material layer was not formed, and the negative electrode plate 13 was produced.

(Production of electrode body)
An electrode body 14 was produced as follows using a core composed of two core rods having a semicircular cross-sectional shape. First, a separator was sandwiched between winding core rods, and only the separator 11 was wound. Next, the positive electrode plate 12 and the negative electrode plate 13 were each inserted between the separators 11 at a predetermined timing, and the positive electrode plate 12 and the negative electrode plate 13 were wound with the separator 11 interposed therebetween. Finally, the end of the outermost winding end was fixed with an insulating tape, and the winding core was pulled out to produce an electrode body 14 having a hollow portion 15 formed at a position corresponding to the winding shaft portion.

(Production of center pin)
The center pin 16 was produced by forming a stainless steel plate having a thickness of 0.25 mm into a cylindrical shape. The cross-sectional shape orthogonal to the length direction of the center pin 16 was a shape in which the C-shaped tip was bent inward.

(Production of cylindrical non-aqueous electrolyte secondary battery)
After the lower insulating plate 18 was disposed below the electrode body 14 and the electrode body 14 was inserted into the outer can 20, the negative electrode lead 13 a was connected to the bottom of the outer can 20. Next, the center pin 16 was inserted into the hollow portion 15 of the electrode body 14, and the upper insulating plate 17 was disposed on the electrode body 14. Groove processing was performed at a position above the upper insulating plate 17 on the side surface of the outer can 20, a gasket 19 was disposed on the groove portion, and the positive electrode lead 12 a was connected to the sealing body 21. Finally, a non-aqueous electrolyte is injected into the outer can 20 and the sealing body 21 is caulked and fixed to the grooved portion of the outer can 20 via the gasket 19, whereby a cylinder having a diameter of 18 mm and a height of 65 mm shown in FIG. A nonaqueous electrolyte secondary battery 10 was produced. The volume energy density of the cylindrical nonaqueous electrolyte secondary battery 10 was 680 Wh / L.

(Examples 2 to 7)
As shown in Table 1, the maximum height Rz of the surface of the base material layer 11a was changed to any value in the range of 0.5 to 3.0 μm. Cylindrical nonaqueous electrolyte secondary batteries 10 according to Examples 2 to 7 were produced. The piercing strengths of the base material layers 11a of Examples 2 to 7 were 410 gf, 415 gf, 410 gf, 407 gf, 410 gf, and 400 gf, respectively.

(Comparative Examples 1 to 3)
Cylindrical non-aqueous electrolyte secondary batteries according to Comparative Examples 1 to 3 in the same manner as in Example 1 except that the maximum height Rz of the base material layer is 0.05 μm, 3.3 μm, or 3.5 μm Was made. Table 1 shows the maximum height Rz of the base material layers of Comparative Examples 1 to 3.

(Safety evaluation)
In order to evaluate the safety of the batteries of Examples 1 to 7 and Comparative Examples 1 to 3, a crush test was performed according to the conditions described in UL1642. That is, the batteries of Examples 1 to 7 and Comparative Examples 1 to 3 charged to 4.2 V were inserted between two flat plates, and pressurization was continued until a load of 13 kN was reached at room temperature. When the load reached 13 kN, the pressurization was stopped and the test was terminated. The voltage and temperature of the battery after the test were measured, and when a temperature increase of 5 ° C. or higher was confirmed, it was determined that there was heat generation. Each of Examples 1 to 7 and Comparative Examples 1 to 3 was tested using five batteries. Table 1 shows the number of batteries determined to have heat generation.

In Comparative Example 1 where the maximum height Rz of the surface of the base material layer is 0.05 μm, heat generation of the battery is confirmed. As a result of disassembling the heated battery and examining the inside, it was found that the heat-resistant layer was peeled off from the base material layer. When the heat-resistant layer is peeled from the base material layer, the thickness of the separator is reduced by the thickness of the heat-resistant layer. For this reason, it is considered that a portion where insulation between the positive and negative electrodes is not sufficiently generated in a part of the inside of the electrode body during the crushing test.

In Comparative Examples 2 and 3 in which the maximum height Rz of the base material layer exceeds 3.0 μm, heat generation of the battery is confirmed in the crush test. The results in Table 1 show a tendency that heat generation is more likely to occur as the maximum height Rz increases. The batteries that generated heat in Comparative Examples 2 and 3 were also disassembled and the inside was examined. As a result, the separator was severely broken on the inner peripheral side of the electrode body. If the maximum height Rz of the base material layer is increased, the adhesion between the base material layer and the heat-resistant layer is improved by the anchor effect. However, if the maximum height Rz is excessively large, when the electrode plate receives a local force from the center pin during the crushing test, the electrode plate pulls the heat-resistant layer, and the base material layer breaks following the heat-resistant layer. It is thought that.

On the other hand, in Examples 1 to 7 in which the maximum height Rz of the base material layer was 0.1 to 3.0 μm, the battery did not generate heat even when subjected to the crush test. By defining the maximum height Rz of the base material layer within the above range, appropriate adhesion between the base material layer and the heat-resistant layer is ensured, and the base layer is pulled when the heat-resistant layer is pulled on the electrode plate. It is considered that the material layer is prevented from following the heat-resistant layer.

In the above embodiment, a cylindrical non-aqueous electrolyte secondary battery having a volume energy density of 680 Wh / L was used. However, the present invention provides a cylindrical non-aqueous electrolyte secondary battery having a volume energy density of 650 Wh / L or more. It is effective.

As described above, according to the present invention, a cylindrical nonaqueous electrolyte secondary battery excellent in safety can be provided. In particular, the present invention is effective for a high-capacity cylindrical nonaqueous electrolyte secondary battery having a volume energy density of 650 Wh / L or more. Therefore, the industrial applicability of the present invention is great.

DESCRIPTION OF SYMBOLS 10 Cylindrical nonaqueous electrolyte secondary battery 11 Separator 11a Base material layer 11b Heat-resistant layer 12 Positive electrode plate 12a Positive electrode lead 13 Negative electrode plate 13a Negative electrode lead 14 Electrode body 15 Hollow part 16 Center pin 17 Upper insulating plate 18 Lower insulating plate 19 Gasket 20 Exterior can 21 Sealing body

Claims

An electrode body in which a positive electrode plate and a negative electrode plate are wound through a separator;
A non-aqueous electrolyte,
A center pin inserted in a hollow portion formed at a position corresponding to the winding shaft portion of the electrode body;
A bottomed cylindrical outer can containing the electrode body and the non-aqueous electrolyte;
The separator includes a base layer composed mainly of polyolefin, and a heat-resistant layer composed mainly of a polymer having heat resistance and formed on at least one surface of the base layer,
The maximum height Rz of the surface of the base material layer is 0.1 μm or more and 3 μm or less,
Cylindrical non-aqueous electrolyte secondary battery.
The cylindrical non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-resistant layer contains insulating inorganic particles.
The inorganic particles are at least one selected from the group consisting of aluminum oxide (Al 2 O 3 ), magnesium oxide (MgO), silicon oxide (SiO 2 ), titanium oxide (TiO 2 ), and zirconium oxide (ZrO 2 ). The cylindrical nonaqueous electrolyte secondary battery according to claim 2.
The cylindrical nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the polymer is at least one selected from the group consisting of polyvinylidene fluoride, polyacrylic acid, polymethacrylic acid, polyamide, and polyimide.
The cylindrical nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the puncture strength of the base material layer is 300 gf or more.
The volume energy density is 650 Wh / L or more, The cylindrical non-aqueous electrolyte secondary battery according to claim 1.