WO2005022674A1

WO2005022674A1 - Battery separator and lithium secondary battery

Info

Publication number: WO2005022674A1
Application number: PCT/JP2004/012499
Authority: WO
Inventors: Kenji Kawabata; Koji Abe
Original assignee: Ube Industries, Ltd.
Priority date: 2003-08-29
Filing date: 2004-08-30
Publication date: 2005-03-10
Also published as: KR20060132556A; KR100977433B1; JPWO2005022674A1; JP4529903B2

Abstract

[PROBLEMS] A separator is disclosed which enables to inject a nonaqueous electrolytic solution easily during production of batteries such as lithium secondary batteries and also enables to produce a battery which is excellent in various battery characteristics. [MEANS FOR SOLVING PROBLEMS] A battery separator wherein a long porous film is provided with a plurality of non-porous linear regions extending in the width direction of the film and at least one surface of the non-porous linear regions is provided with a recessed portion or a projected portion is advantageously used as a battery separator for lithium secondary batteries or the like.

Description

Specification

Battery separator and lithium secondary battery

Technical field

The present invention relates to a battery separator and a lithium secondary battery.

Background art

In recent years, lithium batteries have been widely used as power sources for driving small electronic devices and the like. A lithium battery usually has a configuration in which a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are accommodated in a cylindrical, square, or disk-shaped container. As the positive electrode, a positive electrode mainly composed of a lithium composite oxide such as LiCo O is used, and as the negative electrode, a carbon material or

2

A negative electrode made of lithium metal is generally used. As a separator for the lithium battery, a porous film formed of polyolefin such as polyethylene (PE) or polypropylene (PP), or a porous film formed of a single porous polyethylene film on both sides. A laminated porous film having a configuration in which porous polypropylene films are laminated is used.

[0003] For example, in an assembling process of a cylindrical lithium secondary battery, a positive electrode sheet, a negative electrode sheet, and a separator are overlapped and spirally wound using a metal winding pin to form a battery element ( A wound product is prepared, the wound product is stored in a battery container, and then a non-aqueous electrolyte is injected to manufacture a battery. However, due to recent development competition, lithium secondary batteries have become increasingly high capacity. As a method of increasing the capacity, a method of increasing the volume occupied by the electrode active material in a limited size battery container and decreasing the volume occupied by other members to achieve a high capacity is generally employed. It is used for Therefore, the density of the electrode mixture containing the electrode active material gradually increases, and the thickness of the electrode mixture gradually increases, while the thickness of the current collector and the separator of the electrode mixture must be gradually reduced. It is now. For this reason, the remaining space becomes extremely small, so that it is difficult to inject the nonaqueous electrolyte into the container, and it takes time to inject the nonaqueous electrolyte. Furthermore, it tends to be difficult to uniformly impregnate the non-aqueous electrolyte into the separator after injection.

[0004] Patent Document 1 discloses that a separator and an electrode seal are formed by roughening the surface of the separator. There is disclosed an invention for facilitating the injection of a non-aqueous electrolyte into a battery container in which a rolled product containing a roll containing a separator and a plurality of grooves extending in the width direction of the separator along with the surface roughening. Is also described.

Patent Document 1: JP-A-6-333550

Disclosure of the invention

Problems to be solved by the invention

[0005] The separator described in Patent Document 1 having a roughened surface and provided with a plurality of grooves extending in the width direction does not fit into a battery container in which a rolled product including the separator and the electrode sheet is stored. Although the function of facilitating the injection of the water electrolyte is effective, the mechanical strength and dimensional stability of the separator are reduced due to the surface roughening process and the groove forming process. In particular, as described above, for a recent separator having a tendency to form a thin film, such a decrease in mechanical strength and dimensional stability further deteriorates the reduced mechanical strength and dimensional stability due to thinning. To cause a short circuit.

Means for solving the problem

According to the present invention, a plurality of nonporous linear regions extending in the width direction are formed on a long porous film, and at least one surface of the nonporous linear regions forms a concave portion or a convex portion. Battery separator.

[0007] The present invention also provides a lithium secondary battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator is the separator of the present invention.

[0008] Preferred embodiments of the present invention are described below.

(1) At least one end of the non-porous linear region of the separator extends from the side surface of the separator.

(2) The non-porous linear concave region and the non-porous linear convex region of the separator are alternately arranged along the longitudinal direction of the separator.

(3) The nonporous linear regions of the separator form an oblique lattice.

(4) The non-porous linear regions of the separator are aligned and arranged at a rate of 0.1 to 10 / cm along the longitudinal direction of the separator. (5) Elongated porous film force of a separator A structure in which one porous polyethylene film is laminated on both sides of one porous polyethylene film, respectively.

(6) The non-aqueous electrolyte of the lithium secondary battery contains at least one compound selected from a cyclic carbonate, a chain carbonate, a chain ester, and ratatone.

(7) The non-aqueous electrolyte of the lithium secondary battery contains at least one compound selected from vinylene carbonate, dimethyl vinylene carbonate, butyl ethylene carbonate, high-angle calactone, and divinyl sultone.

The invention's effect

[0009] In a battery such as a lithium secondary battery, when the separator of the present invention is used as a separator, the non-aqueous electrolyte is injected into a battery container containing a wound product including the separator and the electrode sheet. Therefore, the injection time is shortened, and the uniformity of permeation of the nonaqueous electrolyte into the container after the injection is improved. Therefore, when the battery is a secondary battery, the cycle characteristics of the battery are improved as well as the workability of the battery production. Furthermore, since the mechanical strength and dimensional stability of the separator are improved, a short circuit is less likely to occur, and the effect of preventing overcharging also appears.

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] The characteristic configuration of the battery separator of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a partial cross-sectional view of an example of a battery separator according to the present invention, which has a nonporous region and the surface of the nonporous region is a concave portion. The separator in FIG. 1 has a configuration in which a porous polypropylene layer 1, a porous polyethylene layer 2, and a porous polypropylene layer 3 are laminated and bonded, and as a whole, a porous region 5 and a nonporous region 6 are formed. The concave portion 4a is formed on the surface of the non-porous region.

FIG. 2 shows a partial cross-sectional view of a battery separator having a non-porous region of the present invention, and the surface of the non-porous region is a projection. The separator in FIG. 2 has a configuration in which a porous polypropylene layer 1, a porous polyethylene layer 2, and a porous polypropylene layer 3 are laminated and bonded, and as a whole, a porous region 5 and a non-porous region 6 are formed. The convex portion 4b is formed on the surface of the non-porous region. FIG. 3 to FIG. 11 show various examples of the concave or convex pattern on the surface of the battery separator of the present invention.

In FIG. 3, the concave portion or the convex portion has a linear shape extending entirely along the width of the separator.

In FIG. 4, the concave portion or the convex portion has a V-shape that is symmetrical with respect to a center line along the length direction of the separator.

In FIG. 5, the concave portions or convex portions are in the form of oblique lattices extending entirely along the width of the separator.

In FIG. 6, the concave portion or the convex portion has an S-shape extending entirely along the width of the separator.

In FIG. 7, the concave portions and the convex portions alternately extend in a linear shape along the width of the separator.

FIG. 8 shows a shape in which the concave portion has a linear shape extending entirely along the width of the separator, and a linear convex portion extending in the length direction of the separator is additionally provided.

FIG. 9 shows a shape in which the concave portion has a linear shape extending entirely along the width of the separator, and a linear convex portion extending in an oblique direction is additionally provided.

FIG. 10 shows a V-shaped shape in which the concave portion is symmetrical with respect to a center line along the length direction of the separator, and shows a shape in which a circular convex portion is additionally provided.

FIG. 11 shows a shape in which the concave portion has a linear shape extending entirely along the width of the separator, and the dot-shaped convex portions are dispersed and formed.

[0012] The porous film that can be used for the separator of the present invention is a porous film having a large number of penetrating micropores. The porous film that serves as a separator has a high ion permeability, has a predetermined mechanical strength, and is good as long as it is an insulating thin film. Examples of the material include an olefin polymer, a fluorine polymer, a senorelose polymer, and a polyimide. , Polyamide (Ni-Nippon) and glass fiber are used. As a form, a nonwoven fabric, a woven fabric, or a microporous film is used. Particularly preferred materials are polypropylene, polyethylene, a mixture of polypropylene and polyethylene, and a mixture of polypropylene and polyperfluoroethylene. Furthermore, a single-layer porous film of polypropylene or polyethylene and polypropylene and polyethylene Any structure of the laminated porous film which is a mixture of the components may be used. The method for making the porous film porous may be a drawing method (dry method) or an extraction method (wet method).

The nonporous concave portion of the bottom of the separator of the present invention is continuous in a direction of 90 ± 10 degrees with respect to the longitudinal direction of the battery separator, and has a density of 0.1 / cm. The above is preferable 0.3 Zcm or more is more preferable 0.5 Zcm or more is most preferable. On the other hand, 10 lines / cm or less is preferable 5 lines / cm or less is more preferable 3 lines Zcm or less is most preferable

[0014] The depth of the recess separator having the present invention, 2 xm or preferably Ri good more preferably tool is instrument 4 or _M m is most preferable. Meanwhile, most preferably at most 10 xm less preferred instrument 9 _M m or less good Ri preferred tool 8 xm.

The width of the concave portion of the separator of the present invention is preferably 3 μm or more, more preferably 5 μm or more, and most preferably 10 μΐη or more. On the other hand, the width of the concave portion is preferably 500 μ 500η or less, more preferably 300 μm or less, most preferably 200 _β m or less.

The recess may be formed on both sides of the battery separator, which is preferably formed on at least one side. In order to effectively reduce the electrolyte injection time, it is more preferable that concave portions (or convex portions) are alternately provided to the battery separator from both sides. In particular, when the battery is overcharged and gas is generated from the positive electrode, the concave portion of the battery separator works smoothly as a gas release path, so that the concave portion of the battery separator is Preferably.

Although there is no particular limitation on the method of providing the separator with a nonporous concave portion at the bottom, a method of thermocompression bonding between nip rolls is preferable. In the thermocompression bonding, the porous film is formed at a melting point of the material of ± 80 ° C, more preferably ± 30. 0. 1-10kgZcm ² between heated rolls adjusted to a temperature range and C, more preferably dividing lines by crimping at a nip pressure of 1 one 3 kg / cm ^2.

[0018] The concave portions can be provided to the separator either before or after making it porous by a stretching method (dry method) or by an extraction method (wet method), but more preferably after making it porous. In either the stretching method (dry method) or the extraction method (wet method), the film is uniaxially or The film is biaxially stretched to optimize the film thickness, porosity, or porous structure. The provision of the concave portion on the battery separator can be performed before or after the uniaxial stretching or the biaxial stretching. In general, in the stretching method (dry method), since the film is uniaxially stretched in the longitudinal direction to make the film porous, it is preferable that the concave portion is provided after the film separator is stretched so that the dimensional change in the width direction of the battery separator hardly occurs. On the other hand, in the extraction method (wet method), biaxial stretching in which the film is stretched not only in the longitudinal direction but also in the width direction is performed, but it is preferable to provide a concave portion before performing the biaxial stretching.

[0019] Further, in addition to the provision of the concave portion, or without the provision of the concave portion, the separator is provided with a convex portion having a non-porous region force continuous in a direction substantially intersecting the longitudinal direction of the porous film. Is preferred. The protrusions provided on the porous film are continuous in the direction of 90 ± 30 degrees with respect to the longitudinal direction of the separator, and the density is preferably 0.1 / cm or more. Zcm or more is more preferable 0.5 line Zcm or more is most preferable. On the other hand, 10 / cm or less is preferred, 5 / cm or less is more preferred, and 3 / cm or less is most preferred.

[0020] The height of the projection provided on the separator is preferably 2 µΐη or more, more preferably 3 µΐη or more, and most preferably 4 / im or more. On the other hand, the force S is preferably 20 μΐη or less, more preferably 15 / im or less, most preferably 10 μΐη or less.

[0021] The width of the protrusion provided on the separator is preferably 3 µm or more, more preferably 5 µm or more, and most preferably 10 m or more. On the other hand, the force S is preferably 500 m or less, more preferably 200 μΐη or less, which is more preferable than the force S of 300 m or less.

[0022] The protrusions provided to the separator may be formed on at least one surface of the porous film, which is preferably formed on at least one surface. In particular, when the battery is overcharged and gas is generated from the positive electrode, the convex portion of the battery separator works smoothly as a gas release path, so that the convex portion of the battery separator is positive. Les, preferably facing the side.

Regarding the form of the convex portion provided to the separator, the form may be maintained as it is after the injection, or may be dissolved in a non-aqueous electrolyte to make the form disappear. To maintain the shape of the protrusion after injection, use polypropylene, polyethylene, ethylene- A film or filler having a predetermined thickness made of a material selected from the group consisting of copolymer, polybutene 1, propylene butene 1 copolymer, polyimide, and cellulose can be bonded to a battery separator by thermocompression bonding. .

When it is desired to eliminate the form of the projections provided on the battery separator of the present invention after injection, the material for forming the projections may be polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polystyrene, or the like. Polymer materials and copolymers of the above high molecular materials such as ethylene-methacrylic acid copolymer, ethylene-acrylic ester copolymer, and styrene-butadiene copolymer can be used. These materials can lose their form by dissolving in a non-aqueous electrolyte after battery assembly. Further, the melting of the protrusions leads to a reduction in the tightening tension of the battery element after the battery is assembled, so that an effect of preventing damage to the film due to the tightening can be expected.

[0025] There are no particular restrictions on the method of imparting the form of nonporous projections to the separator, and there are a method of dissolving it in a solvent and applying it to the separator, and the method of thermocompression bonding. For example, for a battery separator consisting of three layers of polypropylene / polyethylene / polypropylene, a filament made of polyethylene is thermocompression-bonded in the width direction of the separator, and it is continuous in a direction at about 90 degrees to the longitudinal direction of the separator. A convex portion can be created.

[0026] In the present invention, the concave portion and the convex portion may be a single continuous line or point continuum as long as the nonaqueous electrolyte can be guided in a direction substantially intersecting with the longitudinal direction of the separator. It is preferably at least one kind of continuum of the line segment. These linear structures are preferably shaped so as to be symmetrical when the separator is folded back at its center line along its longitudinal direction, especially linear, grid-shaped, diagonal grid-shaped, V-shaped. More preferably, it has a continuous structure such as a letter shape, a W shape, or an S shape. FIGS. 3 to 6 are schematic plan views of linear, V-shaped, lattice-shaped, and S-shaped patterns in the case where concave portions or convex portions are formed in the separator.

[0027] In order to further improve the liquid injection rate of the battery separator of the present invention, it is preferable to apply the combination of the structures of the concave portion and the convex portion. As the combination structure (type), it is more preferable to provide the concave portions and the convex portions alternately. FIG. 7 shows a schematic plan view of a pattern of a combination structure (type) of a concave portion and a convex portion of a linear alternating type. In the figure The solid line portion indicates a concave portion, and the broken line portion indicates a convex portion.

Further, in the present invention, in order for the non-aqueous electrolyte guided in a direction substantially intersecting with the longitudinal direction of the battery separator to penetrate in the longitudinal direction of the battery separator, the structure of the concave portion and the convex portion is required. In addition, it is preferable to additionally introduce a concave portion or a convex portion having a form selected from a linear shape, a circular shape, and a polygonal shape. In the additional structure, particularly when the form of the convex portion is introduced, it is necessary to arrange the structure uniformly in a direction substantially intersecting the longitudinal direction of the battery separator so as to prevent winding bumps on the battery element. is necessary. Figures 8 to 10 show schematic plan views of the additional type combination structure (type) of concave and convex portions, with additional linear line segments, additional linear line segments (rhombic), and additional V-shaped circles. Shown in The solid line in the figure indicates a concave portion, and the broken line indicates a convex portion.

[0029] The air permeability of the battery separator manufactured as described above is preferably 30 seconds or more and more preferably 50 seconds or more and more preferably 100 seconds or more. . On the other hand, 1000 sec / l OOcc or less is preferable, and 900 sec / l OOcc or less is more preferable. 800 sec / l OOcc or less is most preferable.

[0030] Preferably, the maximum pore diameter is 0.02-3 μm, and more preferably, the porosity is 30-85%, since the capacity characteristics of the battery are improved. Further, the thickness of the battery separator is preferably 5 / im or more in terms of mechanical strength and performance, more preferably 8 μΐη or more, most preferably 以 Ιμΐη or more. On the other hand, 100 μΐη or less is preferred, and 40 / im or less is more preferred, and 30 μm or less is most preferably prepared.

[0031] The constituent members other than the separator in the lithium secondary battery of the present invention are not particularly limited, and various constituent members of a conventionally used lithium secondary battery can be used.

Examples of the non-aqueous electrolyte used together with the battery separator of the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), and γ-petit. Ratatotones (GBL), ratatones such as γ-valerolatatatone, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), getyl carbonate (DEC), methyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, etc. Chain carbonates, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-di Ethers such as ethoxyxetane and 1,2-dibutoxetane, nitriles such as acetonitrile and adiponitrile, phosphates such as trimethyl phosphate and trioctyl phosphate, butyl formate, methyl propionate, methyl bivalate, and butyl bivalate Non-aqueous solvents such as chain esters such as octyl bivalate and amides such as dimethylformamide are used. Among the non-aqueous solvents, it is preferable that at least one selected from cyclic carbonates, ratatones, chain carbonates and chain esters is contained.

[0033] These non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. Examples of the combination include a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a ratatone, a combination of a rataton and a chain ester, a combination of a cyclic carbonate, a ratatone and a chain ester. , Combinations of cyclic carbonates, chain carbonates and ratatatones, combinations of cyclic carbonates and ethers, combinations of cyclic carbonates and chain carbonates and ethers, combinations of cyclic carbonates and chains Various combinations such as a combination of linear carbonates and chain esters are possible, and the mixing ratio is not particularly limited. It is preferable to include at least one of cyclic carbonates and chain carbonates in the non-aqueous solvent. Particularly, when the cyclic carbonates and chain carbonates are contained in combination, the cycle characteristics are excellent and the capacity is high. This is preferable because a battery can be provided.

[0034] Above all, the ratio of the cyclic carbonates to the chain carbonates is preferably 20:80 to 40:60 force S, particularly preferably 25:75 to 35:65 force S in terms of volume ratio. Further, among the above-mentioned chain carbonates, it is preferable to use asymmetric carbonates such as methinoleethynolecarbonate, methinolepropynolecarbonate and methinolebutynolecarbonate. Among them, it is preferable to use methyl carbonate, which is an asymmetric chain carbonate which is a liquid at a low temperature and has a relatively high boiling point and thus little evaporation. Furthermore, among the chain carbonates,

, The capacity of methylethyl carbonate, which is an asymmetric chain carbonate, and dimethyl carbonate and / or getyl carbonate, which are symmetric chain carbonates: 100/0 51/49 Force S preferred, 100/0 70/30 Force S preferred [0035] Among the above combinations, in a combination using ratatones, a ratio that maximizes the capacity ratio of ratatones is preferable.

[0036] Further, at least one selected from double bond-containing compounds such as vinylene carbonate (VC), dimethyl vinylene carbonate, butyl ethylene carbonate, triangular lactone, and divinyl sulfone is added to these non-aqueous solvents. Is preferred.

Further, 1,3-propane sultone (PS), 1,4-butane sultone, pentafluorobenzene methanesulfonate (MSPFB), glycol sulphite, propylene sulphite, glycol sulphate, propylene sulphate, , 4_-butanediol dimethanesulfonate, ethylene glycol dimethanesulfonate, etc. It is preferable to add at least one kind of S = 〇 containing compound.

[0038] A high-capacity battery has a high electrode mixture density, and thus has a poor liquid injection property and a low cycle characteristic. However, together with the battery separator of the present invention, the double bond-containing compound and The addition of the S = 〇-containing compound is preferable since the cycle characteristics are improved.

[0039] If the content of the double bond-containing compound is excessively large, the battery performance may be degraded, and if the content is excessively small, sufficient expected battery performance cannot be obtained. Accordingly, 0.01% by weight or more is preferable, 0.1% by weight or more is more preferable, and 0.5% by weight or more is most preferable, based on the total weight of the nonaqueous electrolyte. On the other hand, 10% by weight or less is preferred, 7% by weight or less is more preferred, and 5% by weight or less is most preferred.

If the content of the S = 〇-containing compound is excessively large, the battery performance may be deteriorated, and if the content is excessively small, sufficient expected battery performance cannot be obtained. Therefore, 0.01% by weight or more is preferable, 0.1% by weight or more is more preferable, and 0.5% by weight or more is most preferable with respect to the total weight of the nonaqueous electrolyte. On the other hand, 10% by weight or less is preferred 7% by weight or less Force is preferred 5% by weight or less is most preferred.

Further, it is preferable to add an aromatic compound together with the separator of the present invention, since it is possible to ensure good battery safety during overcharging. For example, cyclohexynolebenzene, fluorocyclohexylbenzene compounds (1-fluoro-2-cyclohexylbenzene, 1_fluoro-3-cyclohexylbenzene, 1_fluoro-4-cyclohexyl) Benzene), biphenyl, terphenyl (o_ form, m-form, p-form), diphenyl ether, 2-fluorodiphenyl ether, 4-diphenyl ether, fluorobenzene, difluorene benzene (o— Body, m-body, ρ-body), 2_fluorobiphenyl, 4_fluorobiphenyl, 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-diflu Oroanisone, tert-butynolebenzene, 1,3-di-tert-butynolebenzene, 1-funoleo _4_tert_butylbenzene, tert-amylbenzene, 4_tert-butylbiphenyl, tert-amylbiphenylenole, o-terphenyl Hydride (1,2-dicyclohexylbenzene, 2_phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl, m- and p_ If same), m-terphenyl partial hydride, p_ Turf Eniru portion hydrides least one kind is preferably les selected from aromatic compounds. Among them, in the battery using the separator of the present invention, among the aromatic compounds, a cyclohexynolebenzene skeleton, a diphenyl skeleton, or a fluorine-substituted aromatic compound is preferable.

[0042] If the content of the aromatic compound is excessively large, the battery performance may be degraded, and if the content is excessively small, the expected safety cannot be obtained. Therefore, 0.1% by weight or more is preferable, 0.5% by weight or more is more preferable, and 1% by weight or more is most preferable with respect to the total weight of the nonaqueous electrolyte. On the other hand, 10% by weight or less is preferred, 7% by weight or less is more preferred, and 5% by weight or less is most preferred.

In the battery using the separator of the present invention, in particular, by using the aromatic compound in combination with the double bond-containing compound and / or the S = 〇-containing compound, the cycle characteristics and the safety are further improved. Preferred, because we can provide lithium secondary batteries.

[0044] Examples of the electrolyte used in the present invention include LiPF, LiBF, LiCIO, CF SO Li, and the like. LiN (SO CF), LiN (SO C F), LiC (SO CF), LiPF

(CF), LiPF (CF), LiPF (CF), LiPF (iso_CF), LiPF (iso-CF) and other lithium salts containing a chain alkyl group, (CF) (SO) NLi, ( CF) (SO) N

Lithium salts containing a cyclic alkylene chain such as Li are mentioned. These electrolyte salts may be used alone or in combination of two or more. These electrolysis The quality is preferably 0.1 M or more with respect to the above non-aqueous solvent, and more preferably 0.5 M or more.

0.7M or more is most preferable. On the other hand, 3M or less is preferred 2M or less is preferred 1.5

M or less is most preferred.

[0045] The electrolytic solution of the present invention can be obtained, for example, by mixing the above-mentioned non-aqueous solvent and dissolving the above-mentioned electrolyte salt therein.

In addition, by including air or carbon dioxide in the battery of the present invention, for example, it is possible to suppress the generation of gas due to the decomposition of the electrolyte and to improve the battery performance such as cycle characteristics and storage characteristics. it can.

[0047] In the present invention, the method of containing (dissolving) carbon dioxide or air in the non-aqueous electrolyte includes (1) air or carbon dioxide before the non-aqueous electrolyte is injected into the battery in advance. (2) Air or carbon dioxide-containing gas can be contained in the battery either after injection or before or after battery sealing, or a combination of these methods. it can. Air and carbon dioxide-containing gas containing as little moisture as possible have a preferred dew point of 40 ° C or less, and particularly preferably a dew point of 50 ° C or less.

[0048] The entire amount of the electrolytic solution may be injected into the battery of the present invention at one time, but it is preferably performed in two or more steps. Also, it is preferable to reduce the pressure (preferably 500 to 1 tonole, more preferably 400 to 10 torr) or pressurize the battery can to shorten the electrolyte injection time. May be performed.

[0049] As the positive electrode active material, oxides such as MnO and VO, or cobalt, manganese, and nickel oxide are used.

2 2 5

For example, a lithium composite oxide with nickel containing nickel is used. One of these positive electrode active materials may be selected and used, or two or more thereof may be used in combination. Such lithium composite oxides include, for example, LiCoO, LiMnO, LiNi

2 2 4

O, LiCoNiO (0.01 <x <l), LiMnNiCo〇 and the like. Also, LiC

2 l-χ x z y z 1-y-z z

o〇 and LiMn O, LiCoO and LiNiO, LiMn O and LiNiO

2 2 4 2 2 2 4 2

May be used. As described above, as the positive electrode active material, LiCoO, LiMn〇, LiNiO

2 2 4 2

As a positive electrode material, a lithium composite oxide having an open circuit voltage of 4.3 V or more on the Li basis after charging as described above is most preferable, and a lithium composite oxide containing Co or Ni is most preferable. A part of the lithium composite oxide may be replaced by another element

. For example, a part of Co of LiCoO may be replaced with Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, or the like. In particular, the battery separator of the present invention has a great effect in a lithium battery using a positive electrode active material suitable for high voltage and high energy density.

[0050] The conductive agent for the positive electrode may be any electronic conductive material that does not cause a chemical change. Examples include graphites such as natural graphite (flaky graphite and the like) and artificial graphite, and carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black. It is also acceptable to use a mixture of graphite and carbon black as appropriate. The amount of the conductive agent to be added to the positive electrode mixture is preferably 11 to 10% by weight, and particularly preferably 25% by weight.

[0051] The positive electrode comprises the above-mentioned positive electrode active material, a conductive agent such as acetylene black or carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), After kneading with a binder such as copolymer of acrylonitrile and butadiene (NBR) and propyloxymethylcellulose (CMC) to form a positive electrode mixture, this positive electrode material is made of aluminum foil as a current collector and stainless steel lath. It is prepared by applying it to a plate, drying, pressing, and then heating it under vacuum at a temperature of about 50 ° C to 250 ° C for about 2 hours.

As the negative electrode (negative electrode active material), a material capable of occluding and releasing lithium is used. For example, lithium metal, lithium alloy (eg, Al, Sn, Zn, alloy of Si and lithium), tin Tin compounds, silicon, silicon compounds and carbon materials (pyrolyzed carbons, coatas, dalaphites (artificial graphite, natural graphite, etc.), organic polymer compound burners, carbon fibers) are used. In the carbon material, in particular, the lattice spacing (d) of the lattice plane (002) is preferably 0.340 nm or less. The graphite crystal structure having a graphite crystal structure of 0.335-0.337 nm is preferred. It is preferred to use graphites having the following formula: One of these negative electrode active materials may be selected and used, or two or more thereof may be used in combination. In addition, powder materials such as carbon material ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene Copolymer (NBR), power It is used as a negative electrode mixture by kneading with a binder such as ropoxymethylcellulose (CMC). The method for manufacturing the negative electrode is not particularly limited, and the negative electrode can be manufactured by the same method as the above-described method for manufacturing the positive electrode.

[0053] The effect of the additive of the present invention increases as the density of the electrode mixture of the battery increases. In particular, the density of the positive electrode mixture layer formed on the aluminum foil is preferably 3.2-4. OgZcm ^3, more preferably 3.3-3.9 g / cm ³ , and most preferably 3.4-3. 8 g / cm ³ . When the density of the positive electrode mixture exceeds 4. Og / cm ³ , the production becomes substantially difficult. On the other hand, the density of the negative electrode mixture layer formed on the copper foil is 1.3-2. Og / cm ³ , more preferably 1.4-1.9 gZcm ³ , and most preferably 1.5-1.8 g / cm ³ . it is between cm ^3.

In the present invention, the preferable thickness of the positive electrode layer (per one side of the current collector) is 30 to 120 μm, preferably 50 to 100 μm, and the thickness of the negative electrode layer (Per one side of the current collector) is 100 μm, preferably 370 μm.

[0055] The lithium secondary battery of the present invention has excellent cycle characteristics over a long period of time even when the end-of-charge voltage is higher than 4.2V, and particularly when the end-of-charge voltage is 4.3V. It also has excellent cycle characteristics. The discharge end voltage can be 2.5 V or more, and further 2.8 V or more. Although the current value is not particularly limited, it is usually used in a constant current discharge of 0.1 to 3C. In addition, the lithium secondary battery of the present invention has a power capable of charging and discharging in a wide range of -40 to 100 ° C, preferably 0 to 80 ° C.

As a countermeasure against an increase in the internal pressure of the lithium secondary battery in the present invention, a safety valve can be used for the sealing plate. In addition, a method of making a cut in a member such as a battery can or a gasket can also be used. In addition, it is preferable to provide various conventionally known safety elements (at least one of a fuse, a bimetal, and a PTC element as an overcurrent prevention element). It is preferable to use these overcurrent prevention elements together with the shutdown function of the battery separator because safety is greatly improved.

[0057] A plurality of lithium secondary batteries according to the present invention are assembled in series and Z or in parallel as needed, and stored in a battery pack. The battery pack contains safety elements such as PTC elements, thermal fuses, fuses and / or current cutoff elements, as well as safety circuits (each battery and / or Alternatively, a circuit having a function of monitoring the voltage, temperature, current, etc. of the entire assembled battery and interrupting the current may be provided.

[0058] The battery of the present invention can be used for various devices. In particular, it is preferably used for mobile phones, notebook computers, PDAs, video movies, compact cameras, razors, electric tools, automobiles and the like. In particular, for a device having a charging current of 0.5 A or more, the lithium secondary battery of the present invention is preferable because of its high reliability.

Example

Next, the present invention will be specifically described with reference to examples.

[Example 1]

(1) Manufacture of separator

The three-layer structure consisting of a polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer is thermocompression-bonded to an embossing roll heated to 130 ° C. As shown, a linear concave portion having a nonporous bottom (see FIG. 1) was formed continuously in a direction at 90 degrees to the longitudinal direction of the porous long laminated film. The densities of the recesses are 0.2 lines / lcm with respect to the longitudinal direction of the porous long laminated film, the average depth is 8 μm, the average width is 200 μm, and the film thickness is The air permeability was 25.7 μm, the air permeability was 530 sec / 100 cc, the maximum pore diameter was 0, and the porosity was 41%.

(2) Evaluation of electrolyte injection rate

In order to evaluate the effect of improving the electrolyte injection rate of the lithium secondary battery using the above-described separator of the present invention, the following measurement was performed.

The separator was overlapped with a 22-zm-thick aluminum foil and wound into a cylindrical shape to produce a pseudo battery element. The size of the pseudo battery element was 9.5 mm φ (outer diameter) X 60 mm (height) cylindrical. This pseudo battery element was immersed in a non-aqueous electrolyte prepared by dissolving LiPF into 1MZL in a 1: 1 (volZvol) mixed solution of getyl carbonate / propylene carbonate for a specified time, and the weight before and after immersion was measured. did. Figure 12 shows the non-aqueous electrolyte absorption rate (weight change).

(3) In order to evaluate the cycle characteristics and the overcharge prevention effect of the lithium secondary battery of the present invention, the following cylindrical battery was manufactured. (Preparation of non-aqueous electrolyte)

EC: MEC (volume ratio) = 3: 7 A non-aqueous solvent was prepared, and LiPF was added thereto as an electrolyte salt.

After preparing a non-aqueous electrolyte by dissolving to a concentration of M, 2% by weight of vinylene carbonate (VC) and 1% by weight of 1,3-propane sultone (PS) are added to the non-aqueous electrolyte. And cyclohexylbenzene (CHB) was added to a concentration of 2% by weight.

[Production of lithium secondary battery]

90% by weight of LiCoO (positive electrode active material), 5% by weight of acetylene black (conductive agent) and 5% by weight of polyvinylidene fluoride (binder) are mixed with 1-methyl-2-pyrrolidone solvent. The mixture was coated on an aluminum foil, dried, pressed and heated to prepare a positive electrode. 95% by weight of artificial graphite (negative electrode active material) having a graphite-type crystal structure with a lattice spacing (d) of 0.335 nm, and 5% by weight of polyvinylidene fluoride (binder) The mixture was mixed, a 1-methyl-2-pyrrolidone solvent was added thereto, and the mixture was applied on a copper foil, dried, pressed, and heat-treated to prepare a negative electrode. Next, a cylindrical wound product was prepared from the positive electrode, the negative electrode, and the separator, and after injecting the nonaqueous electrolyte, air having a dew point of −60 ° C. was contained in the battery before the battery was sealed. An 18650-size cylindrical battery (diameter 18 mm, height 65 mm) was fabricated. The battery was provided with a pressure release port and an internal current interrupt device (PTC element). At this time, the electrode density of the positive electrode was 3.5 g / cm ³ , and the electrode density of the negative electrode was 1.6 g / cm ³ . The thickness of the positive electrode layer (per one side of the current collector) was 70 μm, and the thickness of the negative electrode layer (per one side of the current collector) was 60 μm.

[Measurement of Battery Characteristics]

The above 18650 battery was charged at a constant current of 2.2A (1C) up to 4.2V at a high temperature (45 ° C), and then charged at a constant voltage of 4.2V for a total of 3 hours under a constant voltage. Next, under a constant current of 2.2 A (1 C), the battery was discharged to a final voltage of 2.8 V, and this charge / discharge was repeated. The initial discharge capacity was almost the same as that of the battery of Comparative Example 1 below. When the battery characteristics after 200 cycles were measured, the discharge capacity retention rate when the initial discharge capacity was 100% was 83.1%. Was. In addition, using an 18650 battery that has been subjected to the cycle test five times, it is overcharged by continuously charging it at a constant current of 2.2A (1C) from a fully charged state of 4.2V at room temperature (20 ° C). As a result of conducting a test and setting the battery surface temperature not to exceed 120 ° C as a safety criterion, The temperature was below 120 ° C.

[Comparative Example 1]

(1) Except that the porous long laminated film having a three-layer structure of the polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer used in Example 1 was used as it was as a separator, In the same manner as in Example 1, the absorption rate (weight change) of the nonaqueous electrolyte was measured. The results are shown in FIG.

(2) Using the above separator, a lithium secondary battery was prepared in the same manner as in Example 1, and the battery characteristics after 200 cycles were measured.The discharge capacity was maintained when the initial discharge capacity was 100%. The rate was 75.7%. When an overcharge test was performed in the same manner as in Example 1, the surface temperature of the battery exceeded 120 ° C. and generated heat.

[Example 2]

(1) Polypropylene (PP) layer Polyethylene filler is thermocompression-bonded to a porous long laminated film consisting of a three-layer structure of Z polyethylene (PE) layer / polypropylene (PP) layer to form a porous length. The laminated film having a cross-section shown in FIG. 2 and having a plurality of non-porous convex regions having the shape shown in FIG. 3 was obtained. The density of the protrusions was 0.2 lines / lcm with respect to the longitudinal direction of the separator, the average height was 15 / im, and the average width was 25 / im.

(2) The non-aqueous electrolyte solution absorption rate (weight change) was measured in the same manner as in Example 1 except that the above separator was used. Figure 13 shows the results.

(3) A lithium secondary battery was prepared using the above separator in the same manner as in Example 1, and the battery characteristics after 200 cycles were measured.The discharge capacity was maintained when the initial discharge capacity was set to 100%. The rate was 82.6%. When an overcharge test was performed in the same manner as in Example 1, the surface temperature of the battery was 120 ° C. or lower.

[Example 3]

(1) Polypropylene (PP) layer A porous long laminated film consisting of a three-layer structure of a Z polyethylene (PE) layer / polypropylene (PP) layer, the shape of which is shown in FIG. A plurality of non-porous regions of the concave portion having a cross section shown in FIG. 1 having such an oblique lattice shape were formed to obtain a separator according to the present invention. (2) The nonaqueous electrolyte solution absorption rate (weight change) was measured in the same manner as in Example 1 except that the above separator was used. Fig. 14 shows the results.

(3) A lithium secondary battery was prepared using the above separator in the same manner as in Example 1, and the battery characteristics after 200 cycles were measured.The discharge capacity was maintained when the initial discharge capacity was set to 100%. The rate was 81.9%. When an overcharge test was performed in the same manner as in Example 1, the surface temperature of the battery was 120 ° C. or lower.

[0068] [Comparative Example 2]

(1) The procedure was performed except that the porous long laminated film having a three-layer structure of the polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer used in Example 3 was used as a separator. In the same manner as in Example 1, the non-aqueous electrolyte solution absorption rate (weight change) was measured. Fig. 14 shows the results.

Brief Description of Drawings

FIG. 1 shows a partial cross-sectional view of an example of a battery separator of the present invention.

FIG. 2 shows a partial cross-sectional view of another example of the battery separator of the present invention.

FIG. 3 shows an example of a concave or convex pattern on the surface of the battery separator of the present invention.

FIG. 4 shows another example of a pattern of concave portions or convex portions on the surface of the battery separator of the present invention.

FIG. 5 shows another example of a concave or convex pattern on the surface of the battery separator of the present invention.

FIG. 6 shows another example of a concave or convex pattern on the surface of the battery separator of the present invention.

FIG. 7 shows another example of a pattern of concave portions or convex portions on the surface of the battery separator of the present invention.

FIG. 8 shows another example of a pattern of concave portions or convex portions on the surface of the battery separator of the present invention.

FIG. 9 shows another example of a pattern of concave portions or convex portions on the surface of the battery separator of the present invention. FIG. 10 shows another example of a concave or convex pattern on the surface of the battery separator of the present invention.

FIG. 11 shows another example of a pattern of concave portions or convex portions on the surface of the battery separator of the present invention.

FIG. 12 shows the production of a lithium secondary battery using the battery separator of the present invention of Example 1 and the production of a lithium secondary battery using the separator of Comparative Example 1 having no concave or convex portions formed. FIG. 4 is a diagram showing a change in an absorption rate of a non-aqueous electrolyte.

FIG. 13 shows the production of a lithium secondary battery using the battery separator of the present invention of Example 2 and the production of a lithium secondary battery using the separator of Comparative Example 1 in which no concave portion or convex portion was formed. It is a figure showing change of the absorption rate of a nonaqueous electrolyte.

FIG. 14 shows the production of a lithium secondary battery using the battery separator of the present invention in Example 3, the formation of a concave portion or a convex portion, and the use of a lithium secondary battery using the separator of Comparative Example 2. It is a figure which shows the change of the absorption rate of the nonaqueous electrolyte solution of battery manufacture.

Explanation of symbols

1 Porous polypropylene layer

2 Porous polyethylene layer

3 Porous polypropylene layer

4 recess

5 Porous area

6 Non-porous area

7 convex

Claims

The scope of the claims

[1] A plurality of nonporous linear regions extending in the width direction are formed on a long porous film.

A battery separator in which at least one surface of the non-porous linear region forms a concave portion or a convex portion.

[2] The separator according to claim 1, wherein at least one end of the non-porous linear region extends from a side surface of the separator.

[3] The separator according to claim 1, wherein the non-porous linear concave region and the non-porous linear convex region are alternately arranged along the longitudinal direction of the separator.

[4] The separator according to claim 1, wherein the non-porous linear region forms an oblique lattice.

[5] The separator according to claim 1, wherein the nonporous linear regions are arranged at a rate of 0.1 to 10 / cm along the longitudinal direction of the separator.

[6] The separator according to claim 1, wherein the long porous film has a configuration in which one porous polypropylene film is laminated on both sides of one porous polyethylene film.

[7] A lithium battery including a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the separator includes a plurality of nonporous linear regions extending in a width direction of the long porous film. A lithium secondary battery formed as a separator, wherein at least one surface of the non-porous region has a concave portion or a convex portion.

[8] The lithium secondary battery according to claim 7, wherein the non-aqueous electrolyte contains at least one compound selected from a group consisting of cyclic carbonate, chain carbonate, chain ester, and rataton.

[9] The non-aqueous electrolyte contains at least one compound selected from vinylene carbonate, dimethylvinylene carbonate, butylene carbonate, polyangialactone, and divinyl sultone. Lithium secondary battery described in