KR100977433B1 - Battery separator and lithium secondary battery - Google Patents

Abstract

(Problem) In the manufacture of batteries, such as a lithium secondary battery, the separator which makes it easy to inject | pour a nonaqueous electrolyte solution and is excellent in various battery characteristics is provided.

(Solution means) As a battery separator such as a lithium secondary battery, a plurality of non-linear linear regions extending in the width direction are formed in an elongate porous film, and at least one surface of the non-porous linear region is a concave portion or a convex portion. A battery separator that forms a portion is advantageously used.

Lithium Secondary Battery, Separator, Nonporous, Electrolyte, Porous

Description

Battery separator and lithium secondary battery {BATTERY SEPARATOR AND LITHIUM SECONDARY BATTERY}

Technical Field

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

Background

In recent years, lithium batteries are widely used as power sources for driving such as small electronic devices. A lithium battery generally consists of a structure which accommodates a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte in the inside of a cylindrical, square or disk shaped container. A positive electrode, the positive electrode is mainly composed of a lithium composite oxide, such as LiCo0 ₂ is used, a negative electrode, the negative electrode made of a carbon material or lithium metal is generally used. The separator for lithium batteries includes a porous film formed of polyolefin such as polyethylene (PE) and polypropylene (PP), or one porous polypropylene film laminated on both sides of one porous polyethylene film. Laminated porous films are used.

For example, in the assembly process of a cylindrical lithium secondary battery, a positive electrode sheet, a negative electrode sheet, and a separator are piled up, and a battery element (winding object) is created by winding in a vortex shape using a metal winding pin, and this winding After storing an ash in a battery container, a battery is manufactured by pouring a nonaqueous electrolyte. However, due to the recent development competition, lithium secondary batteries have become increasingly high in capacity. As a method of high capacity, the method which enlarges the volume occupied by the electrode active material in the battery container of a limited size, makes the volume occupied by other members small, and achieves high capacity is generally used. Therefore, the density of the electrode mixture containing the electrode active material is gradually increased, the thickness of the electrode mixture is gradually increased, while the thickness of the current collector and the separator of the electrode mixture is gradually reduced. For this reason, since the remaining space becomes extremely small, the pouring of the non-aqueous electrolyte into the container becomes difficult, and the pouring takes time. Moreover, there exists a tendency for uniform impregnation of the nonaqueous electrolyte solution after pouring into a separator.

Patent Document 1 discloses an invention that facilitates injection of a nonaqueous electrolyte into a battery container in which a wound object including a separator and an electrode sheet is contained by roughening the surface of the separator, and with the roughening of the surface, It also describes forming a plurality of grooves extending in the width direction of the separator.

Patent Document 1: Japanese Patent Application Laid-open No. Hei 6-333550

Disclosure of Invention

Problems to be Solved by the Invention

The separator which roughened the surface of the said patent document 1, and provided the some groove extended in the width direction has a function which makes it easy to inject | pour nonaqueous electrolyte solution into the battery container in which the winding object containing a separator and an electrode sheet was accommodated. Although it is effective in terms of, the mechanical strength and the dimensional stability of the separator are lowered due to the roughening process and the groove forming process. In particular, as mentioned above, in the recent separators which tend to be thinned, such a decrease in mechanical strength and dimensional stability becomes thinner and further deteriorates the degraded mechanical strength and dimensional stability, which easily causes short circuits.

Means to solve the problem

The present invention is a battery separator in which a plurality of nonporous linear regions extending in the width direction are formed in an elongate porous film, and at least one surface of the nonporous linear regions forms a concave portion or a convex portion.

The present invention is also a lithium battery containing a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and the separator is also a lithium secondary battery, wherein the separator is the separator of the present invention.

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-linear linear concave region and the non-linear linear convex region of the separator are alternately arranged along the longitudinal direction of the separator.

(3) The non-porous linear region of the separator forms an oblique grating.

(4) The non-porous linear regions of the separator are arranged in a ratio of 0.1 to 10 / cm along the longitudinal direction of the separator.

(5) The elongate porous film of the separator has a structure in which one porous polypropylene film is laminated on both sides of one porous polyethylene film, respectively.

(6) The nonaqueous electrolyte of the lithium secondary battery contains at least one compound selected from cyclic carbonates, chain carbonates, chain esters, and lactones.

(7) The nonaqueous electrolyte of the lithium secondary battery contains at least one compound selected from vinylene carbonate, dimethylvinylene carbonate, vinyl ethylene carbonate, α-angelicalactone, and divinyl sulfone.

Effects of the Invention

In a battery such as a lithium secondary battery, when the separator of the present invention is used as a separator, injection of the non-aqueous electrolyte into the battery container containing the wound material containing the separator and the electrode sheet is facilitated, thereby shortening the injection time. In addition, the uniformity of penetration of the nonaqueous electrolyte into the container after injection is improved. For this reason, not only the workability of battery preparation but also the improvement of the cycling characteristics of a battery when a battery is a secondary battery appears. In addition, since the mechanical strength and dimensional stability of the separator are improved, short circuiting is unlikely to occur, and the effect of preventing overcharge is also exhibited.

To practice the invention  Best form for

The characteristic structure of the battery separator of this invention is demonstrated in detail, referring an accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS The partial cross section of the example of the battery separator of this invention which has a non-porous area | region and whose surface is a recessed part is shown. The separator of FIG. 1 has a configuration in which the porous polypropylene layer 1, the porous polyethylene layer 2, and the porous polypropylene layer 3 are laminated and bonded, and as a whole, the porous region 5 and the non-porous region It consists of (6) and the recessed part 4a is formed in the surface of a non-porous area | region.

Fig. 2 shows a partial cross-sectional view of a battery separator that has a nonporous region of the present invention and whose surface is a convex portion. The separator of FIG. 2 has a configuration in which the porous polypropylene layer 1, the porous polyethylene layer 2, and the porous polypropylene layer 3 are laminated and bonded, and as a whole, the porous region 5 and the non-porous region ( 6), and the convex part 4b is formed in the surface of a non-porous area | region.

3-11 shows various examples of the pattern of the recessed part or convex part of the surface of the battery separator of this invention.

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

In FIG. 4, the recessed part or convex part is in the V-shape which becomes symmetrical with respect to the centerline along the longitudinal direction of a separator.

In Fig. 5, the concave portion or convex portion is in the shape of an oblique grating extending entirely along the width of the separator.

In FIG. 6, the recessed part or convex part is in the shape of the S-shape extended all along the width of a separator.

In FIG. 7, the concave portion and the convex portion alternately extend in a straight line along the width of the separator.

In FIG. 8, the recessed part exists in the linear form extended all along the width of a separator, and the linear convex part extended in the longitudinal direction of a separator is shown in this figure.

In FIG. 9, the recessed part exists in the linear form extended all along the width of a separator, and the linear convex part extended in an oblique direction is shown in this figure.

In FIG. 10, the recessed part exists in the V-shape which becomes symmetrical with respect to the centerline along the longitudinal direction of a separator, and shows the shape in which the circular convex part was provided in parallel.

In FIG. 11, the recessed part exists in the linear form extended all along the width of a separator, and the point which the convex-shaped convex part is disperse | distributed is shown in this.

The porous film which can be used for the separator of this invention is a porous film which has many through micropores. The porous film to be a separator has a high ion permeability, has a predetermined mechanical strength, and may be an insulating thin film. Examples of the material include an olefin polymer, a fluorine polymer, a cellulose polymer, a polyimide, a polyamide (nylon), and a glass fiber. Is used. As a form, a nonwoven fabric, a woven fabric, and a microporous film are used. In particular, as the material, a mixture of polypropylene, polyethylene, polypropylene and polyethylene, and a mixture of polypropylene and polyperfluoroethylene are preferable. Moreover, any structure may be sufficient as the single layer porous film of polypropylene or polyethylene, and the laminated porous film which is a mixture of polypropylene and polyethylene. The porous method of the porous film may be either the stretching method (dry method) or the extraction method (wet method).

The recessed portion in which the bottom portion of the separator of the present invention is non-porous is continuous in the direction of 90 ± 10 degrees with respect to the longitudinal direction of the battery separator, and the density thereof is preferably 0.1 pieces / cm or more, and 0.3 pieces / cm or more. More preferably, 0.5 or more pieces / cm are the most preferable. On the other hand, 10 pieces / cm or less are preferable, 5 pieces / cm or less are more preferable, and 3 pieces / cm or less are the most preferable.

2 micrometers or more are preferable, as for the depth of the recessed part which the separator of this invention has, 3 micrometers or more are more preferable, and 4 micrometers or more are the most preferable. On the other hand, 10 micrometers or less are preferable, 9 micrometers or less are more preferable, and 8 micrometers or less are the most preferable.

3 micrometers or more are preferable, as for the width | variety of the recessed part which the separator of this invention has, 5 micrometers or more are more preferable, and 10 micrometers or more are the most preferable. On the other hand, 500 micrometers or less are preferable, 300 micrometers or less are more preferable, and 200 micrometers or less are the most preferable width of a recessed part.

The recess is preferably formed on at least one side of the battery separator, and may be formed on both sides. In order to effectively shorten the electrolyte injection time, it is more preferable to provide recesses (or projections) alternately from the front and back to the battery separator. In particular, when the battery is in an overcharged state and gas is generated from the positive electrode, it is preferable that the concave portion provided to the battery separator smoothly acts as a gas leakage path, so that the concave portion of the battery separator faces the positive electrode side.

Although there is no restriction | limiting in particular about the method of providing a recessed part whose bottom part is nonporous to a separator, The method of thermocompression bonding between nip rolls is suitable. Thermocompression is a nip pressure of 0.1 to 10 kg / cm 2, more preferably 1 to 3 kg / cm 2 between heating rolls in which the porous film is adjusted to a melting point of the material at a temperature range of ± 80 ° C., more preferably ± 30 ° C. By pressing.

Although provision of the recessed part to a separator can be performed before and after pore-forming by the extending | stretching method (dry method) or the extraction method (wet method), it is more preferable to carry out after pore-forming. In either of the stretching method (dry method) or the extraction method (wet method), the film is stretched uniaxially or biaxially to optimize the film thickness, porosity or porous structure. The provision of the recesses to the battery separator can be performed either before or after uniaxial stretching or biaxial stretching. In general, in the stretching method (dry method), since the film is uniaxially stretched in the longitudinal direction to be porous, the dimensional change in the width direction of the battery separator is unlikely to occur, and it is preferable to provide a recess after stretching. On the other hand, in extraction method (wet method), although biaxial stretching extending | stretching not only about the longitudinal direction of a film but also about the width direction is performed, it is preferable to provide a recessed part before biaxial stretching.

In addition, it is preferable that the convex part which consists of non-porous regions continuous in the direction substantially crossing a longitudinal direction of a porous film is provided in addition to laying a recessed part in a separator. The convex portions provided on the porous film are continuous in the direction of 90 ± 30 degrees with respect to the longitudinal direction of the separator, the density is preferably 0.1 pieces / cm or more, more preferably 0.3 pieces / cm or more, and 0.5 pieces / cm The above is most preferable. On the other hand, 10 pieces / cm or less are preferable, 5 pieces / cm or less are more preferable, and 3 pieces / cm or less are the most preferable.

2 micrometers or more are preferable, as for the height of the convex part attached to a separator, 3 micrometers or more are more preferable, and 4 micrometers or more are the most preferable. On the other hand, 20 micrometers or less are preferable, 15 micrometers or less are more preferable, and 10 micrometers or less are the most preferable.

3 micrometers or more are preferable, as for the width | variety of the convex part attached to a separator, 5 micrometers or more are more preferable, and 10 micrometers or more are the most preferable. On the other hand, 500 micrometers or less are preferable, 300 micrometers or less are more preferable, and 200 micrometers or less are the most preferable.

It is preferable that the convex part provided to a separator is formed in at least single side | surface of a porous film, and may be formed in both surfaces. In particular, when the battery is in an overcharged state and gas is generated from the positive electrode, it is preferable that the convex portion provided to the battery separator smoothly acts as a gas leak path, so that the convex portion of the battery separator faces the positive electrode side.

About the form of the convex part provided to the separator, you may maintain the form as it is after pouring, and may melt | dissolve in a non-aqueous electrolyte solution and may lose the form. In the case where the shape of the convex portion is maintained after pouring, a predetermined thickness made of a material selected from the group consisting of polypropylene, polyethylene, ethylene-α olefin copolymer, polybutene 1, propylene-butene 1 copolymer, polyimide, and celluloses Film or filler can be attached to the battery separator by thermocompression bonding.

In the case where the form of the convex portion provided to the battery separator of the present invention is to be lost after the pouring, a polymer material such as polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polystyrene, and ethylene- Copolymers of the above-mentioned high molecular materials, such as methacrylic acid copolymer, an ethylene-acrylic ester copolymer, and a styrene-butadiene copolymer, can be used. These materials can be lost in form by dissolving them in a non-aqueous electrolyte after battery assembly. In addition, since the dissolution of the convex portion is also connected to the winding tension of the battery element after battery assembly, the effect of preventing the breakage of the film due to the winding and the like can also be expected.

There is no restriction | limiting in particular in the method of giving a form of a non-porous convex part to a separator, There exist a method of melt | dissolving in a solvent and apply | coating to a separator, or the method of thermocompression bonding. For example, with respect to a battery separator having a three-layered structure of polypropylene / polyethylene / polypropylene, polyethylene filaments are thermally compressed in the width direction thereof, and convex portions continuous in the direction of about 90 degrees with respect to the longitudinal direction of the separator. I can write it.

In the present invention, the concave portion and the convex portion may have a structure capable of guiding the nonaqueous electrolyte solution in a direction substantially intersecting with the longitudinal direction of the separator. desirable. These linear structures are preferably symmetrical when the separator is folded back from the center line along its longitudinal direction, and in particular, straight, lattice, oblique lattice, V-shape, W-shape, S-shape, etc. It is more preferable that it consists of a continuous structure. 3 to 6 are schematic plan views of the straight, V-shaped, lattice-shaped, and S-shaped shapes in the case where the concave portion or the convex portion is formed in the separator.

In order to further improve the pouring speed of the battery separator of the present invention, it is preferable to combine the structures of the concave portion and the convex portion. As a combination structure (type), it is more preferable to provide the said recessed part and convex part alternately. The schematic plan view of a linear alternating type is shown in FIG. 7 regarding the shape of the combination structure (type) of a recessed part and a convex part. The solid line part in a figure shows a recessed part, and a broken line part shows a convex part.

In addition, in the present invention, in order to infiltrate the nonaqueous electrolyte guided in the direction substantially intersecting the longitudinal direction of the battery separator in the longitudinal direction of the battery separator, in addition to the concave and convex structures, in the linear, circular, and polygonal shapes, It is preferable to appropriately introduce additional recesses or projections of the selected form. In the above additional structure, particularly in the case of introducing the shape of the convex portion, it is necessary to arrange the structure uniformly in the direction substantially intersecting the longitudinal direction of the battery separator so that the winding nose portion does not occur in the battery element. Regarding the shapes of the additional type combined structure (type) of the concave portion and the convex portion, schematic plan views of the linear line segment addition type, the linear line segment addition type (rectangle), and the V-shaped circular addition type are shown in Figs. The solid line part in a figure shows a recessed part, and a broken line part shows a convex part.

As for the air permeability of the battery separator manufactured as mentioned above, 30 second / 100 Pa or more is preferable, 50 second / 100 Pa or more is more preferable, 100 second / 100 Pa or more is most preferable. On the other hand, 1000 second / 100 ms or less is preferable, 900 second / 100 ms or less is more preferable, 800 second / 100 ms or less is the most preferable.

The maximum pore size is preferably 0.02 to 3 µm, and the porosity of 30 to 85% is preferable because the capacity characteristics of the battery are improved. In addition, the thickness of the battery separator is preferably 5 µm or more, more preferably 8 µm or more, and most preferably 10 µm or more in view of mechanical strength, performance, and the like. On the other hand, 100 micrometers or less are preferable, 40 micrometers or less are more preferable, and 30 micrometers or less are most preferably prepared.

The constituent members other than the separator in the lithium secondary battery of the present invention are not particularly limited, and constituent members of various lithium secondary batteries that have been conventionally used can be used.

As a nonaqueous electrolyte used with the said battery separator of this invention, cyclic carbonates, such as ethylene carbonate (EC), a propylene carbonate (PC), butylene carbonate (BC), (gamma) -butyrolactone ( GBL), lactones such as γ-valerolactone, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate and dibutyl carbonate Ethers such as chain carbonates, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane , Nitriles such as acetonitrile and adiponnitrile, phosphate esters such as trimethyl phosphate and trioctyl phosphate, chain esters such as butyl formate, methyl propionate, methyl pivalate, butyl pivalate and octyl pivalate, Dimethylformamide Non-aqueous solvents, such as amides, are used. Among the nonaqueous solvents, at least one selected from cyclic carbonates, lactones, chain carbonates and chain esters is preferably contained.

These nonaqueous solvents are usually used in admixture in order to achieve appropriate physical properties. The combination is, for example, a combination of cyclic carbonates and chain carbonates, a combination of cyclic carbonates and lactones, a combination of lactones and chain esters, a cyclic carbonate, lactones and chain Combinations of esters, combinations of cyclic carbonates and chain carbonates and lactones, combinations of cyclic carbonates and ethers, combinations of cyclic carbonates and chain carbonates and ethers, cyclic carbonates and Various combinations, such as a combination of a linear carbonate and a linear ester, are mentioned, The mixing ratio is not specifically limited. It is preferable to contain at least one of cyclic carbonates and chain carbonates in the nonaqueous solvent. Particularly, the combination of cyclic carbonates and chain carbonates can provide a battery having excellent cycle characteristics and high capacity. It is preferable because it is.

Especially, as for the ratio of cyclic carbonate and chain carbonate, 20: 80-40: 60 are preferable at a capacity ratio, and 25: 75-35: 65 are especially preferable. Moreover, it is preferable to use asymmetric carbonates, such as methyl ethyl carbonate, methyl propyl carbonate, and methyl butyl carbonate, among the said linear carbonates. Especially, since it is liquid at low temperature and has a relatively high boiling point, it is preferable to use methyl ethyl carbonate of the asymmetrical chain | strand carbonates with little evaporation. Furthermore, it is preferable that the volume ratio of methyl ethyl carbonate which is an asymmetrical chain carbonate, and dimethyl carbonate and / or diethyl carbonate which are symmetrical chain carbonates is 100/0-51/49 among chain carbonates, and it is 100 / 0-70 / 30 are more preferable.

Moreover, in the combination which uses lactone among the said combinations, the ratio by which the capacity ratio of lactones becomes largest is preferable.

In addition, it is preferable to add at least one selected from double bond-containing compounds such as vinylene carbonate (VC), dimethylvinylene carbonate, vinyl ethylene carbonate, α-angelicalactone and divinyl sulfone to these nonaqueous solvents. .

Further, 1,3-propanesultone (PS), 1,4-butanesultone, methanesulfonate pentafluorobenzene (MSPFB), glycol sulfite, propylene sulfite, glycol sulfate, propylene sulfate, 1,4- It is preferable to add at least one or more selected from S═O-containing compounds such as butanediol dimethanesulfonate and ethylene glycol dimethanesulfonate.

The battery having a high capacity has a high electrode mixture density, and thus the liquid-liquidity deteriorates and the cycle characteristics are deteriorated. However, by adding the double bond-containing compound and / or the S = 0-containing compound together with the battery separator of the present invention, This is preferable because the cycle characteristics are improved.

If the content of the double bond-containing compound is excessively large, battery performance may be lowered. If the content of the double bond-containing compound is excessively small, sufficient battery performance expected is not obtained. Therefore, 0.01 weight% or more is preferable with respect to the weight of the whole nonaqueous electrolyte solution, 0.1 weight% or more is more preferable, and 0.5 weight% or more is the most preferable. On the other hand, 10 weight% or less is preferable, 7 weight% or less is more preferable, and 5 weight% or less is the most preferable.

When there is too much content of the said S = 0 containing compound, battery performance may fall, and when too small, sufficient battery performance anticipated cannot be obtained. Therefore, 0.01 weight% or more is preferable with respect to the weight of the whole nonaqueous electrolyte, 0.1 weight% or more is more preferable, 0.5 weight% or more is the most preferable. On the other hand, 10 weight% or less is preferable, 7 weight% or less is more preferable, and 5 weight% or less is the most preferable.

In addition, it is preferable to add an aromatic compound together with the separator of the present invention to ensure good battery safety during overcharge. For example, cyclohexylbenzene, fluorocyclohexylbenzene compound (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), ratio Phenyl, terphenyl (o-form, m-form, p-form), diphenylether, 2-fluorodiphenylether, 4-diphenylether, fluorobenzene, difluorobenzene (o-form, m- Sieve, p-body), 2-fluorobiphenyl, 4-fluorobiphenyl, 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, tert -Butylbenzene, 1,3-di-tert-butylbenzene, 1-fluoro-4-tert-butylbenzene, tert-amylbenzene, 4-tert-butylbiphenyl, tert-amylbiphenyl, o-terphenyl Partial hydrides of (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl, hereinafter m-form, p-form) selected from aromatic compounds such as partial hydride of m-terphenyl and partial hydride of p-terphenyl Even more than one kinds are preferable. Especially, in the battery using the separator of this invention, it is preferable that it is a cyclohexylbenzene skeleton, a diphenyl skeleton, or a fluorine-substituted aromatic compound among the said aromatic compounds.

If the content of the aromatic compound is excessively large, battery performance may be lowered. If the content of the aromatic compound is excessively small, sufficient safety expected is not obtained. Therefore, 0.1 weight% or more is preferable with respect to the weight of the whole nonaqueous electrolyte, 0.5 weight% or more is more preferable, and 1 weight% or more is the most preferable. On the other hand, 10 weight% or less is preferable, 7 weight% or less is more preferable, and 5 weight% or less is the most preferable.

In the battery using the separator of the present invention, in particular, by using the aromatic compound and the double bond-containing compound and / or the S = O-containing compound together, a lithium secondary battery excellent in cycle characteristics and safety can be provided. desirable.

Examples of the electrolyte used in the present invention include LiPF ₆ , LiBF ₄ , LiClO ₄ , CF ₃ SO ₃ Li, and the like. LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF Lithium salts containing a chain alkyl group such as ₃ (CF ₃ ) ₃ , LiPF ₃ (iso-C ₃ F ₇ ) ₃ , LiPF ₅ (iso-C ₃ F ₇ ), or (CF ₂ ) ₂ (SO ₂ ) _{2 NLi, (CF 2) 3} (SO 2) there may be mentioned lithium salt containing a cyclic alkyl chain, such as ₂ NLi. These electrolyte salts may be used by one type, or may be used in combination of 2 or more type. 0.1 M or more is preferable with respect to said nonaqueous solvent, 0.5 M or more is more preferable, and 0.7 M or more is most preferable for these electrolytes. On the other hand, 3M or less is preferable, 2M or less is more preferable, 1.5M or less is the most preferable.

The electrolyte solution of this invention is obtained by mixing the said nonaqueous solvent, for example, and dissolving the said electrolyte salt in this.

Furthermore, by containing air or carbon dioxide in the battery of the present invention, for example, suppression of gas generation due to decomposition of the electrolyte solution, battery performance such as cycle characteristics and storage characteristics can be improved.

In the present invention, a method of containing (dissolving) carbon dioxide or air in a nonaqueous electrolyte includes (1) a method in which the nonaqueous electrolyte is contacted with air or a carbon dioxide-containing gas before being injected into a battery, and (2) after pouring Any method of incorporating air or carbon dioxide-containing gas into the battery before or after battery sealing may be used, or a combination thereof may be used. It is preferable that air and a carbon dioxide containing gas do not contain water as much as possible, It is preferable that it is dew point -40 degrees C or less, It is especially preferable that it is dew point -50 degrees C or less.

Although the electrolyte solution whole quantity may be inject | poured in the battery of this invention at once, it is preferable to carry out in 2 or more steps. Moreover, in order to shorten electrolyte injection time etc., it is preferable to pressurize or depressurize a battery can (preferably 500-1torr, more preferably 400-10torr), and you may apply a centrifugal force or an ultrasonic wave to a battery can.

As the positive electrode active material, an oxide such as Mn0 ₂ , V ₂ O ₅ , or a lithium composite oxide with lithium containing cobalt, manganese, or nickel is used. Only one type may be used for these positive electrode active materials, and may be used for them combining two or more types. As such a lithium composite oxide, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _{1 - x} Ni _x O _z (0.01 <x <1), LiMn _y Ni _z Co _{1- y- z} O _z , and the like. Also it may be used by appropriately mixing such as LiCoO ₂ and LiMn ₂ O _4, LiCoO ₂ and LiNiO _2, LiMn ₂ O ₄ and LiNiO _2. , As a positive electrode active material as described above, LiCoO _2, LiMn ₂ O _4, a lithium complex oxide as the open-circuit voltage after charging ends, such as LiNiO ₂ represents at least 4.3V based on Li as is preferred, and most preferred as the cathode material , Lithium composite oxide containing Co or Ni may be used, and part of the lithium composite oxide may be substituted with an ellipsoid. For example, part of Co of LiCoO ₂ may be substituted 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.

The conductive agent of the positive electrode may be any electron conducting material that does not cause chemical change. For example, graphite, such as natural graphite (flake-like graphite), artificial graphite, carbon black, such as acetylene black, Ketjen black, Chennel black, furnace black, lamp black, and thermal black, etc. are mentioned. Moreover, you may use it, mixing graphite and carbon black suitably. 1-10 weight% is preferable and, as for the addition amount with respect to positive mix of a electrically conductive agent, 2-5 weight% is especially preferable.

The positive electrode is a positive electrode active material such as acetylene black, carbon black and other conductive agents, poly tetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), acrylonitrile and butadiene After kneading with a binder such as copolymer (NBR) and carboxymethyl cellulose (CMC) to form a positive electrode mixture, the positive electrode material is applied to an aluminum foil or stainless steel lath plate as a current collector, and then dried and press-molded. It is produced by heating under vacuum at a temperature of about 50 ° C to 250 ° C for about 2 hours.

As a negative electrode (cathode active material), the material which can occlude and release lithium is used, For example, lithium metal, a lithium alloy (for example, alloy of Al, Sn, Zn, Si, and lithium), tin, or a tin compound , Silicon, silicon compounds and carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compound combustion bodies, carbon fibers) are used. In the carbon material, it is particularly preferable that the surface spacing d ₀₀₂ of the lattice plane 002 is 0.340 nm or less, and graphite having a graphite crystal structure of 0.335 to 0.337 nm is preferably used. Only one type may be used for these negative electrode active materials, and may be used for them combining two or more types. In addition, powder materials such as carbon materials ethylene propylene diene polymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), copolymers of styrene and butadiene (SBR), acrylonitrile and butadiene It is used as a negative electrode mixture by kneading with a binder such as copolymer (NBR) and carboxymethyl cellulose (CMC). The manufacturing method of a negative electrode is not specifically limited, It can manufacture by the same method as the manufacturing method of the said positive electrode.

The effect of the additive of this invention is so large that the electrode mixture density of a battery is high. In particular, the density of the positive electrode mixture layer formed on the aluminum foil is preferably 3.2 to 4.0 g / cm 3, more preferably 3.3 to 3.9 g / cm 3, most preferably 3.4 to 3.8 g / cm 3. When the positive electrode mixture density becomes larger than 4.0 g / cm 3, practically, the production becomes difficult. On the other hand, the density of the negative electrode mixture layer formed on the copper foil is between 1.3 and 2.0 g / cm 3, more preferably between 1.4 and 1.9 g / cm 3 and most preferably between 1.5 and 1.8 g / cm 3.

In addition, the thickness (per current collector single side) of the electrode layer of the said positive electrode in this invention is 30-120 micrometers, Preferably it is 50-100 micrometers, The thickness (per current collector single side) of the electrode layer of the said cathode is 1- 100 micrometers, Preferably it is 3-70 micrometers.

The lithium secondary battery according to the present invention has excellent cycle characteristics over a long period even when the charge end voltage is larger than 4.2V, and particularly has a good cycle characteristic even when the charge end voltage is equal to 4.3V. The discharge end voltage can be 2.5 V or more and 2.8 V or more. Although it does not specifically limit regarding a current value, Usually, it is used by the constant current discharge of 0.1-3C. Moreover, although the lithium secondary battery in this invention can be charged and discharged in a wide range at -40-100 degreeC, Preferably it is 0-80 degreeC.

A safety valve can be used for a sealing plate as a countermeasure of the internal pressure rise of the lithium secondary battery in this invention. In addition, the method of forming a cutting depth in members, such as a battery can and 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 said battery separator, since safety improves very much.

The lithium secondary battery in this invention is accommodated in a battery pack combining several in series and / or parallel as needed. In addition to safety devices such as PTC elements, temperature fuses, fuses and / or current interrupting devices, the battery pack has a function to cut off currents by monitoring the voltage, temperature, and current of each battery and / or assembled battery as a whole. Circuit).

The battery of the present invention can be used in various devices. In particular, it is preferable to be used for a mobile phone, a notebook computer, a PDA, a video movie, a compact camera, a razor, a power tool, an automobile. In particular, the lithium secondary battery of the present invention has high reliability and is preferable for equipment having a charging current of 0.5 A or more.

Example

Next, an Example is given and this invention is demonstrated concretely.

Example 1

(1) Manufacture of separator

As shown in FIG. 3, by thermocompression bonding the porous elongate laminated film which consists of three layers of a polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer to the embossing roll heated at 130 degreeC, A straight concave portion (see FIG. 1) having a non-porous bottom portion continuous in the direction of 90 degrees with respect to the longitudinal direction of the porous elongate laminated film was created. The densities of the recesses were 0.2 // 1 cm apart with respect to the longitudinal direction of the porous elongated laminated film, the depth of which was 8 탆 on average, the width of which was 200 탆 on average, the film thickness was 25.7 탆, and the air permeability was 530 seconds /. The maximum pore diameter was 0.12 µm and the porosity was 41%.

(2) Evaluation of electrolyte injection speed

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

The separator was laminated with a 22 μm-thick aluminum foil and wound in a cylindrical shape to form a pseudo battery element. The size of the pseudo battery element was a cylindrical shape of 9.5 mm phi (outer diameter) x 60 mm (height). This pseudo battery element was immersed in a non-aqueous electrolyte prepared by dissolving LiPF ₆ in a 1: 1 (vol / vo1) mixed solution of diethyl carbonate / propylene carbonate at 1 M / L for a predetermined time, and the weight before and after immersion was measured. The nonaqueous electrolyte absorption rate (weight change) is shown in FIG.

(3) In order to evaluate the cycle characteristic and the overcharge prevention effect of the lithium secondary battery of this invention, the cylindrical battery demonstrated below was produced.

[Preparation of nonaqueous electrolyte]

A nonaqueous solvent having an EC: MEC (volume ratio) of 3: 7 was prepared, and LiPF ₆ was dissolved therein as an electrolyte salt to a concentration of 1 M to prepare a nonaqueous electrolyte, and then vinylene carbonate (VC) was added to the nonaqueous electrolyte. 2% by weight, 1,3-propanesultone (PS) was added to 1% by weight and cyclohexylbenzene (CHB) to 2% by weight.

[Production of a lithium secondary battery]

90% by weight of LiCoO ₂ (anode active material), 5% by weight of acetylene black (conductive agent), and 5% by weight of polyvinylidene fluoride (binder) were mixed, and 1-methyl-2-pi was added thereto. The mixture which added and mixed the lollidon solvent was apply | coated on aluminum foil, and it dried, press-molded, and heat-processed, and prepared the positive electrode. Artificial graphite (negative electrode active material) having the spacing of lattice plane (002) (d ₀₀₂₎ is a graphite-type crystal structure 0.335㎚ mixture of 95% by weight, polyvinylidene fluoride (binder) in a proportion of 5% by weight Then, the 1-methyl-2-pyrrolidone solvent was added to this, the mixed thing was apply | coated on copper foil, and it dried, press-molded, and heat-processed to prepare the negative electrode. Next, a cylindrical wound is made from these positive and negative electrodes and a separator, and after injecting the nonaqueous electrolyte, air at a dew point of −60 ° C. is contained in the battery before closing the battery, and a cylindrical battery of 18650 size (18 mm in diameter, Height 65 mm) was produced. The cell was formed with a pressure opening and an internal current interrupter (PTC device). 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 (per current collector single side) of the electrode layer of the positive electrode was 70 μm, and the thickness (per current collector single side) of the negative electrode layer was 60 μm.

[Measurement of Battery Characteristics]

Using the above 18650 battery, the battery was charged to a constant current of 2.2 A at a constant current of 2.2 A (1 C) at a high temperature (45 ° C.), and then charged as a final voltage of 4.2 V under a constant voltage for a total of 3 hours. 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 charging and discharging was repeated. The initial discharge capacity was almost the same as that of the battery of Comparative Example 1 below, and the battery characteristics after 200 cycles were measured. When the initial discharge capacity was 100%, the discharge capacity retention rate was 83.1%. In addition, using an 18650 battery, which was repeated five times in a cycle test, an overcharge test was conducted by continuously charging at a constant current of 2.2 A (1C) at a full charge of 4.2 V under normal temperature (20 ° C) to perform an overcharge test to obtain a surface temperature of the battery. The surface temperature of the battery was 120 ° C. or less as a result of the safety standard indicating that the temperature did not exceed 120 ° C.

Comparative Example 1

(1) Except having used the porous elongate laminated film which consists of three layers of the polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer which were used in Example 1 as a separator as it is, In the same manner, the nonaqueous electrolyte absorption rate (weight change) was measured. The result is shown in FIG.

(2) A lithium secondary battery was prepared in the same manner as in Example 1 using the above separator, and the battery characteristics after 200 cycles thereof were measured. As a result, the discharge capacity retention rate when the initial discharge capacity was 100% was 75.7. Was%. In the same manner as in Example 1, the overcharge test was conducted, and as a result, the surface temperature of the battery was higher than 120 ° C.

[Example 2]

(1) To the porous elongate laminated film composed of a three-layered configuration of a polypropylene (PP) layer, a polyethylene (PE) layer, and a polypropylene (PP) layer, a polyethylene filler was thermocompression-bonded to a porous elongated laminated film. 2, the cross section shown in FIG. 2, the some non-convex part area | region of the shape as shown in FIG. 3 were formed, and the separator which concerns on this invention was obtained. Density of the convex part was 0.2 piece / 1cm space | interval with respect to the longitudinal direction of a separator, the height was 15 micrometers in average, and the width was 25 micrometers in average.

(2) Except having used the said separator, it carried out similarly to Example 1, and measured the non-aqueous electrolyte liquid absorption speed | rate (weight change). The result is shown in FIG.

(3) A lithium secondary battery was produced in the same manner as in Example 1 using the above separator, and the battery characteristics after 200 cycles thereof were measured. As a result, the discharge capacity retention rate when the initial discharge capacity was 100% was 82.6. Was%. In addition, as in Example 1, as a result of the overcharge test, the surface temperature of the battery was 120 ° C. or less.

Example 3

(1) The porous elongate laminated film composed of a three-layered configuration of a polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer was formed in the same manner as in Example 1, as shown in FIG. 5. A plurality of non-porous regions having the same oblique lattice shape and the concave portions shown in FIG. 1 were formed to obtain a separator according to the present invention.

(2) Except having used the said separator, it carried out similarly to Example 1, and measured the non-aqueous electrolyte liquid absorption speed | rate (weight change). The result is shown in FIG.

(3) A lithium secondary battery was produced in the same manner as in Example 1 using the above separator, and the battery characteristics after 200 cycles thereof were measured. As a result, the discharge capacity retention rate when the initial discharge capacity was 100% was 81.9. Was%. In addition, as in Example 1, the overcharge test was conducted, and as a result, the surface temperature of the battery was 120 ° C or lower.

Comparative Example 2

(1) Except having used the porous elongate laminated film which consists of three layers of the polypropylene (PP) layer / polyethylene (PE) layer / polypropylene (PP) layer which were used in Example 3 as a separator as it is, In the same manner, the nonaqueous electrolyte absorption rate (weight change) was measured. The result is shown in FIG.

Brief description of the drawings

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

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

Fig. 3 shows an example of a pattern of recesses or projections on the surface of the battery separator of the present invention.

4 shows another example of a pattern of recesses or projections on the surface of the battery separator of the present invention.

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

FIG. 6 shows another example of the pattern of recesses or projections on the surface of the battery separator of the present invention. FIG.

The other example of the pattern of the recessed part or convex part of the surface of the battery separator of this invention is shown.

The other example of the pattern of the recessed part or convex part of the surface of the battery separator of this invention is shown.

The other example of the pattern of the recessed part or convex part of the surface of the battery separator of this invention is shown.

The other example of the pattern of the recessed part or convex part of the surface of the battery separator of this invention is shown.

FIG. 11 shows another example of the pattern of recesses or protrusions on the surface of the battery separator of the present invention. FIG.

[Fig. 12] Absorption rate of the nonaqueous electrolyte in 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 in which no concave or convex portions are formed. It is a figure which shows the change of.

FIG. 13 Absorption rate of the nonaqueous electrolyte in 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 recesses or protrusions are formed. It is a figure which shows the change of.

14] Absorption rate of a nonaqueous electrolyte solution in the manufacture of a lithium secondary battery using the battery separator of the present invention of Example 3 and in the manufacture of a lithium secondary battery using the separator of Comparative Example 2 in which no recesses or protrusions were formed. It is a figure which shows the change of.

Explanation of the sign

1: porous polypropylene layer

2: porous polyethylene layer

3: porous polypropylene layer

4: recess

5: porous area

6: nonporous region

7: convex

Claims (9)

In the elongate porous film, a plurality of nonporous linear regions extending in the width direction are formed, and at least one surface of the nonporous linear regions forms a concave portion or a convex portion, The said elongate porous film has a structure which one porous polypropylene film is laminated | stacked on both sides of one porous polyethylene film, respectively, The battery separator. The method of claim 1, At least one end of the non-porous linear region extends from the side surface of the separator, wherein the separator for batteries is used. The method of claim 1, A battery separator, wherein the non-linear linear concave regions and the non-linear linear convex regions are alternately arranged along the longitudinal direction of the separator. The method of claim 1, A battery separator, wherein the non-porous linear region forms an oblique grating. The method of claim 1, A battery separator, wherein the non-porous linear regions are arranged in a ratio of 0.1 to 10 / cm along the longitudinal direction of the separator. delete As a lithium battery containing a positive electrode, a negative electrode, the battery separator of Claim 1, and a nonaqueous electrolyte solution, The separator is a separator in which a plurality of non-linear linear regions extending in the width direction thereof are formed in an elongated porous film, and at least one surface of the non-porous linear region forms a concave portion or a convex portion. Lithium secondary battery. The method of claim 7, wherein The non-aqueous electrolyte solution contains at least one compound selected from cyclic carbonates, chain carbonates, chain esters, and lactones. The method of claim 7, wherein The non-aqueous electrolyte contains at least one compound selected from vinylene carbonate, dimethylvinylene carbonate, vinyl ethylene carbonate, α-angelicalactone, and divinyl sulfone.

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