JP2009123484A - Separator and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator having high shut down responsiveness in overheat and reducing shrink in overheat without damaging ion permeability; and to provide a battery using the separator and having high safety in overheat. <P>SOLUTION: In a separator 4 comprising a porous substrate layer 4A having a shutdown function made of a polyolefin resin for example and a porous heat resistant resin layer 4B made of an aramid resin for example, the chlorine content contained in the whole separator is limited to 500-5000 ppm in a mass basis. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a separator that is interposed between a positive electrode and a negative electrode of a battery and prevents a short circuit between the two, and a battery using the separator, for example, a lithium ion battery, a nickel hydrogen battery, a nickel cadmium battery, a lithium-manganese dioxide battery. , Relating to batteries such as lithium-iron sulfide batteries.

Due to the remarkable development of electronic technology in portable devices in recent years, portable electronic devices such as mobile phones, camera-integrated video tape recorders, and notebook personal computers are recognized as basic technologies that support an advanced information society.
Along with this, research and development related to the enhancement of the functionality of these electronic devices has been energetically promoted, and the increase in power consumption due to the enhancement of the functionality of the devices has led to a reduction in drive time. In order to secure time, since the improvement of the energy density in the secondary battery used as a drive power supply is an essential condition, for example, a lithium ion secondary battery is expected.

In order to ensure the safety of such a battery, a mechanism for interrupting current when the battery generates heat is incorporated. For example, a separator made by stretching a polyolefin has a shutdown mechanism that blocks current by closing holes formed by stretching near the melting point.
However, when shutting down, shrinkage occurs in the separator, which may cause secondary problems such as an internal short circuit.

In order to cope with such a problem, a porous film made of at least two kinds of resin materials of a porous resin layer made of para-aromatic polyamide and a porous resin made of a thermoplastic polymer is used as a battery separator. It has been proposed that when the temperature rises, the gap of the para-aromatic polyamide resin layer is closed by melting a resin made of a thermoplastic polymer to shut it down (see Patent Document 1).
In addition, it has been proposed to use a separator having a structure in which a polyolefin porous membrane is used as a substrate and a heat-resistant resin layer is provided as a second layer (see Patent Document 2).
Furthermore, it has also been proposed to use a separator having a multilayer structure composed of two types of porous thermoplastic resin membranes whose melting points differ by a certain temperature or more (see Patent Document 3).
Japanese Patent No. 3721039 JP 2000-100408 A Japanese Patent Laid-Open No. 5-13062

However, the separator having the structure described in Patent Document 1 has a poor shutdown response to a temperature rise and is insufficient to maintain the safety of the battery.
On the other hand, the separator described in Patent Document 2 can improve the response of shutdown during overheating and reduce the shrinkage of the separator. However, by providing a heat resistant resin layer, the ion permeability is hindered, and this is used. However, there was a problem that the charge / discharge cycle characteristics were inferior. In addition, the separator described in Patent Document 3 has a shutdown action, but there is a difference in melting point, but because each layer is thermoplastic, the shrinkage of the separator is not improved, and when exposed to high temperatures The possibility of an internal short circuit is not improved.

  The present invention has been made to solve the above-mentioned problems in the prior art, and its object is to reduce the shrinkage at the time of overheating while being excellent in the shutdown response at the time of overheating without impairing the ion permeability. It is an object of the present invention to provide a separator that can achieve the above and a battery that includes such a separator and has excellent safety during overheating.

  As a result of intensive studies to achieve the above object, the present inventors have found that a chloride added to improve solubility when a heat-resistant resin is dissolved in a polar organic solvent such as N-methyl-pyrrolidone. The inventors have found that the above-mentioned object can be achieved by an appropriate amount of ions remaining in the separator, and have completed the present invention.

That is, the separator of the present invention comprises a porous base material layer having a shutdown function and a porous heat-resistant resin layer, and the chlorine content relative to the whole separator is 500 to 5000 ppm on a mass basis.
The battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, a separator, and the separator comprises a porous base material layer having a shutdown function, and a porous heat-resistant resin layer, and the chlorine content relative to the whole separator Is 500 to 5000 ppm on a mass basis.

  According to the present invention, since the chlorine content in the separator composed of the porous base material layer and the porous heat-resistant resin layer is 500 to 5000 ppm of the whole separator on a mass basis, it has good ion permeability and has a shutdown response at the time of overheating. It is possible to provide a separator excellent in safety and having a small amount of shrink and a battery having such a separator and excellent in safety.

  Hereinafter, the separator of the present invention and a battery using the separator will be described in detail. In the present specification, “%” represents mass percentage unless otherwise specified.

  The separator of the present invention is suitably used for various batteries, and as described above, includes a porous base material layer having a shutdown function and a porous heat-resistant resin layer, and the chlorine content of the separator is based on the whole. It is 500 to 5000 ppm on a mass basis, so that the ion permeability is improved, the porous base material layer ensures the shutdown function of the separator, and the heat-resistant resin layer can reduce the shrinkage during overheating.

The details of the action and effect obtained by setting the chlorine ion concentration in the range of 500 to 5000 ppm are not necessarily clear at present, but the residual chlorine changes the phase separation rate of the resin in the coating layer, and the permeation of ions. It is thought that the porous structure which makes it easy to be formed is formed.
That is, when the chlorine content in the separator is less than 500 ppm, the heat generation rate at the time of battery collapse cannot be reduced sufficiently, and conversely, if the chlorine content exceeds 5000 ppm, the initial capacity of the battery is reduced. To do.

  In the present invention, the porous substrate to which the heat-resistant resin layer is applied is usually used as a battery separator, and when overheated, it softens or melts and clogs the opening to block the current. It does not specifically limit if it shows a shutdown function, For example, the porous film which consists of polyolefin resin, such as polyethylene (PE) and polypropylene (PP), or the mixture of these polyolefin resin can be used.

  On the other hand, the heat-resistant resin layer in the present invention means a resin having a heat resistance of 100 ° C. or higher, usually called engineering plastic, and particularly preferably a heat-resistant resin having a heat resistance of 150 ° C. or higher and a glass transition point of 150 ° C. or higher. Can be used. Specifically, polyamide (aramid), polyimide, polyamideimide, or a blend resin of two or more of these resins can be suitably used.

  The battery system to which the separator of the present invention can be applied is not particularly limited, as described above, such as lithium ion battery, nickel metal hydride battery, nickel cadmium battery, lithium-manganese dioxide battery, lithium-iron sulfide battery, etc. In the ion battery system, the battery is suitably used for a battery designed for a charging voltage of 4.20 V or more. The above-mentioned heat-resistant resin used for the separator of the present invention is preferably used because it has high oxidation resistance as compared with a separator that is usually used, and hardly deteriorates even at a high charging pressure.

That is, the battery of the present invention comprises a positive electrode, a negative electrode, an electrolyte, the separator, that is, a porous base material layer having a shutdown function, and a porous heat-resistant resin layer, and the chlorine content relative to the whole separator is 500 to 500 on a mass basis. It has a separator of 5000 ppm, has excellent safety during overheating, and can exhibit excellent characteristics particularly in a battery having an open circuit voltage per single cell in a fully charged state of 4.2 V to 4.6 V.
Here, the fully charged state means a final state when the battery is charged by a current value of 0.5 C or less or a constant current-constant voltage method (the constant voltage unit is a voltage cut with a current value of 0.1 C or less). C is charging current value (mA) / battery capacity or electrode capacity (mA). In addition, the charging potential of the positive electrode in a fully charged state can be measured, for example, by opening a hole through which the electrolytic solution can enter and exit the battery, immersing the battery in a test cell into which the electrolytic solution has been injected, and using lithium as a reference electrode. it can.

  In addition, as for the battery shape of the present invention, a battery constituent member such as a cylindrical battery, a square battery, a button battery, a coin battery, a sheet battery, a flat battery, etc. having an inside-out structure, a wound structure, etc. There is no particular limitation as long as the structure can accommodate this structure.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross-sectional structure of a nonaqueous electrolyte battery according to a first embodiment of the present invention.
This battery is called a so-called cylindrical type, and is a wound electrode in which a strip-shaped positive electrode 2 and a strip-shaped negative electrode 3 are wound through a separator 4 inside a battery can 1 having a substantially hollow columnar shape. It has a body 20.

The battery can 1 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 1, a pair of insulating plates 5 and 6 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.
At the open end of the battery can 1, a battery lid 7, a safety valve mechanism 8 provided inside the battery lid 7, and a heat sensitive resistance element (PTC element: Positive Temperature Coefficient) 9 are interposed via a gasket 10. It is attached by caulking, and the inside of the battery can 1 is sealed. The battery lid 7 is made of, for example, the same material as the battery can 1.

The safety valve mechanism 8 is electrically connected to the battery lid 7 via the heat sensitive resistance element 9, and when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating, the disc plate 11 is It reverses and the electrical connection of the battery cover 7 and the winding electrode body 20 is cut | disconnected.
The heat-sensitive resistor element 9 limits the current by increasing the resistance value when the temperature rises, and prevents abnormal heat generation due to a large current. The gasket 10 is made of an insulating material, and asphalt is applied to the surface.

The wound electrode body 20 is wound around, for example, the center pin 12. A positive electrode lead 13 made of aluminum or the like is connected to the positive electrode 2 of the wound electrode body 20, and a negative electrode lead 14 made of nickel or the like is connected to the negative electrode 3.
The positive electrode lead 13 is electrically connected to the battery lid 7 by welding to the safety valve mechanism 8, and the negative electrode lead 14 is electrically connected to the battery can 1 by welding.

FIG. 2 is an enlarged view of a part of the spirally wound electrode body 20 shown in FIG. 1. As shown in this figure, the positive electrode 2 includes, for example, a strip-shaped positive electrode current collector 2A, A positive electrode mixture layer 2B provided on both surfaces of the positive electrode current collector 2A. On the other hand, the negative electrode 3 includes a negative electrode current collector 3A having a strip shape and a negative electrode mixture layer 3B provided on both surfaces of the negative electrode current collector 3A. The positive electrode 2 and the negative electrode 3 will be described later. It faces through the separator 4.
Here, the structure in which the positive electrode mixture layer 2B and the negative electrode mixture layer 3B are provided on both surfaces of the positive electrode current collector 2A and the negative electrode current collector 3A is illustrated, but the positive electrode current collector 2A and the negative electrode current collector are illustrated. It is also possible to have a region where the positive electrode mixture layer 2B and the negative electrode mixture layer 3B are provided only on one side of the body 3A.

[Positive electrode]
The positive electrode current collector 2A forming a part of the positive electrode 2 is made of, for example, a metal foil such as an aluminum (Al) foil, and the positive electrode mixture layer 2B contains a positive electrode active material, and if necessary, A conductive agent such as graphite and a binder such as polyvinylidene fluoride may be included.

As the positive electrode active material, a positive electrode material capable of inserting and extracting lithium can be used. As a specific positive electrode material, for example, a lithium-containing compound such as lithium oxide, lithium phosphorous oxide, lithium sulfide, or an intercalation compound containing lithium is suitable, and a mixture of two or more of these may be used. Good.
In order to increase the energy density, a lithium-containing compound containing lithium (Li), a transition metal element, and oxygen (O) is preferable. Among them, as the transition metal element, cobalt (Co), nickel (Ni), manganese (Mn And at least one selected from the group consisting of iron (Fe).

As such a lithium-containing compound, for example, the following formula (1), more specifically, a lithium composite oxide having an average composition represented by the formula (2), an average composition represented by the formula (3) Examples thereof include lithium composite oxides.
_{Li p Ni (1-q-} r) Mn q M1 r O (2-y) X z ··· (1)
(Wherein M1 is at least one element selected from Groups 2 to 15 excluding nickel (Ni) and manganese (Mn), X is at least selected from Groups 16 and 17 other than oxygen (O)) One element, p, q, r, y, z is 0 ≦ p ≦ 1.5, 0 ≦ q ≦ 1.0, 0 ≦ r ≦ 1.0, −0.10 ≦ y ≦ 0.20, (Indicates a value within the range of 0 ≦ z ≦ 0.2.)

Li _a Co _1-b M2 _b O _2-c (2)
(M2 in the formula is vanadium (V), copper (Cu), zirconium (Zr), zinc (Zn), magnesium (Mg), aluminum (Al), gallium (Ga), yttrium (Y) and iron (Fe). At least one element selected from the group consisting of a, b, and c is in the range of 0.9 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.3, −0.1 ≦ c ≦ 0.1 (Note that the composition of lithium varies depending on the state of charge and discharge, and the value of a represents the value in a fully discharged state.)

_{Li w Ni x Co y Mn z} M3 1-x-y-z O 2-v ··· (3)
(M3 in the formula is vanadium (V), copper (Cu), zirconium (Zr), zinc (Zn), magnesium (Mg), aluminum (Al), gallium (Ga), yttrium (Y) and iron (Fe). At least one element selected from the group consisting of: v, w, x, y, z is −0.1 ≦ v ≦ 0.1, 0.9 ≦ w ≦ 1.1, 0 <x <1, 0 <y <1, 0 <z <0.5, 0 ≦ 1-xyz The values of lithium vary depending on the state of charge and discharge, and the value of w indicates a fully discharged state. Represents the value at.)

Further, examples of the lithium-containing compound include a lithium composite oxide having a spinel structure represented by the following formula (4), more specifically, LidMn 2 O 4 (d≈1).
_{Li p Mn 2-q M4 q} O r F s ··· (4)
(M4 in the formula is cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe) At least one element selected from the group consisting of copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr) and tungsten (W), p , Q, r, and s indicate values in the range of 0.9 ≦ p ≦ 1.1, 0 ≦ q ≦ 0.6, 3.7 ≦ r ≦ 4.1, and 0 ≦ s ≦ 0.1. Note that the composition of lithium varies depending on the state of charge and discharge, and the value of p represents the value in a fully discharged state.)

Furthermore, examples of the lithium-containing compound include lithim complex phosphate having the olivine structure represented by the following formula (5), more specifically, the formula (6), and more specifically. Examples include LieFePO ₄ (e≈1).
Li _a M5 _b PO ₄ (5)
(In the formula, M5 is at least one element selected from Group 2 to Group 15, and a and b are values in the range of 0 ≦ a ≦ 2.0 and 0.5 ≦ b ≦ 2.0. )

Li _t M6PO ₄ (6)
(M6 in the formula is cobalt (Co), manganese (Mn), iron (Fe), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V). , Niobium (Nb), copper (Cu), zinc (Zn), molybdenum (Mo), calcium (Ca), strontium (Sr), tungsten (W) and zirconium (Zr) And t represents a value within a range of 0.9 ≦ t ≦ 1.1, wherein the composition of lithium varies depending on the state of charge and discharge, and the value of t represents a value in a fully discharged state.

In addition to the positive electrode material described above, examples of a positive electrode material capable of inserting and extracting lithium (Li) include inorganic materials such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS that do not contain lithium. A compound can be mentioned.

[Negative electrode]
The negative electrode current collector 3A forming a part of the negative electrode 3 is made of, for example, a metal foil such as a copper (Cu) foil, and the negative electrode mixture layer 3B absorbs and releases lithium as a negative electrode active material. 1 type or 2 types or more of the negative electrode material which can be comprised, and it is comprised including the binder similar to the positive mix layer 2B as needed.

  In this nonaqueous electrolyte battery, the electrochemical equivalent of the negative electrode material capable of occluding and releasing lithium is larger than the electrochemical equivalent of the positive electrode 2, and lithium metal is added to the negative electrode 3 during charging. Does not precipitate.

  In addition, this nonaqueous electrolyte battery is designed such that the open circuit voltage (that is, the battery voltage) in a fully charged state is in the range of 4.2 V to 4.6 V, for example. For example, when the open circuit voltage in the fully charged state is 4.25 V or more, even when the same positive electrode active material is used, the amount of lithium released per unit mass is larger than that of a 4.2 V battery. Therefore, the amount of the positive electrode active material and the negative electrode active material is adjusted accordingly, and thereby a high energy density can be obtained.

  Examples of negative electrode materials capable of inserting and extracting lithium include graphite, non-graphitizable carbon, graphitizable carbon, pyrolytic carbons, cokes, glassy carbons, and fired organic polymer compounds And carbon materials such as carbon fiber and activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and is partially non-graphitizable carbon or graphitizable carbon. Some are classified as: Examples of the polymer material include polyacetylene and polypyrrole.

  These carbon materials are preferable because the change in the crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent characteristics can be obtained. Furthermore, those having a low charge / discharge potential, specifically, those having a charge / discharge potential close to that of lithium metal are preferable because a high energy density of the battery can be easily realized.

Further, examples of the negative electrode material capable of inserting and extracting lithium include materials capable of inserting and extracting lithium and including at least one of a metal element and a metalloid element as a constituent element. be able to. If such a material is used, a high energy density can be obtained. In particular, it is more preferable to use such a material together with a carbon material because a high energy density can be obtained and excellent cycle characteristics can be obtained.
This negative electrode material may be a single element or an alloy or a compound of a metal element or a metalloid element, and may have one or two or more of these phases at least in part. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. Some of the structures include a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them.

  Examples of the metal element or metalloid element constituting such a negative electrode material include magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), and germanium. (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) or platinum (Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, those containing a 4B group metal element or semi-metal element in the short-period type periodic table as a constituent element are preferable, and particularly preferable are those containing at least one of silicon and tin as a constituent element. . Silicon and tin have a large ability to occlude and release lithium (Li), and can obtain a high energy density.

As an alloy of tin (Sn), for example, as a second constituent element other than tin (Sn), silicon (Si), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese Selected from the group consisting of (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb) and chromium (Cr) The thing containing at least 1 sort (s) of element is mentioned.
As an alloy of silicon (Si), for example, as a second constituent element other than silicon (Si), tin (Sn), nickel (Ni), copper (Cu), iron (Fe), cobalt (Co), manganese (Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb) and chromium (Cr) at least The thing containing 1 type is mentioned.

  Examples of the tin (Sn) compound or silicon (Si) compound include those containing oxygen (O) or carbon (C). In addition to tin (Sn) or silicon (Si), the above-described compounds are used. Two constituent elements may be included.

Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Examples of other metal compounds include oxides such as MnO ₂ , V ₂ O ₅ , and V ₆ O ₁₃ , sulfides such as NiS and MoS, and lithium nitrides such as LiN _3. Includes polyacetylene, polyaniline, polypyrrole and the like.

[Electrolytes]
As the electrolyte, a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent can be used. As a non-aqueous solvent, it is preferable that at least one of ethylene carbonate and propylene carbonate is included from the point which can improve cycling characteristics, for example. In particular, it is more preferable to mix and contain both ethylene carbonate and propylene carbonate because the cycle characteristics can be further improved.
Furthermore, as the non-aqueous solvent, those containing at least one of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate are preferable. This is because the cycle characteristics can be further improved.

Further, the non-aqueous solvent preferably contains at least one of 2,4-difluoroanisole and vinylene carbonate.
The inclusion of 2,4-difluoroanisole can improve the discharge capacity, and the inclusion of vinylene carbonate can further improve the cycle characteristics. In particular, it is more preferable that they are mixed and contained because both the discharge capacity and the cycle characteristics can be improved.

  Examples of the non-aqueous solvent include butylene carbonate, γ-butyrolactone, γ-valerolactone, those obtained by substituting some or all of the hydrogen groups of these compounds with fluorine groups, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl Tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, trimethyl phosphate and the like may be included. .

  Furthermore, depending on the electrode to be combined, the reversibility of the electrode reaction may be improved by using a material in which some or all of the hydrogen atoms of the substances contained in the nonaqueous solvent group described above are substituted with fluorine atoms. Therefore, these substances can be appropriately used as the non-aqueous solvent.

On the other hand, the lithium salt as the electrolyte salt, _{e.g., LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5) 4, LiCH 3 SO 3, LiCF 3 SO 3, LiN (SO 2 CF 3 ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBF ₂ (ox) [lithium difluorooxalate borate], LiBOB (lithium bisoxalate borate), or LiBr, which are suitable. Any one or two or more of them can be mixed and used.
Among these, LiPF ₆ is preferable because high ion conductivity can be obtained and cycle characteristics can be improved. Further, when charged with a high charging voltage, for example, although aluminum is a positive electrode current collector is easily dissolved in the presence of LiPF _6, it is possible to form a film on the aluminum surface by the LiPF ₆ decomposes Thereby, dissolution of aluminum can be suppressed.

[Separator]
The separator 4 separates the positive electrode 2 and the negative electrode 3 and has a function of allowing lithium ions to pass while preventing a short circuit of current due to contact between both electrodes, and is shown enlarged in FIGS. 3 (a) and 3 (b). As described above, a structure including a porous base material layer 4A and a porous heat-resistant resin layer 4B provided on one or both surfaces of the base material layer 4A is provided.
In contrast to FIG. 3B, the porous heat-resistant resin layer 4B can be sandwiched between the porous base material layers 4A, or a multilayer structure of four or more layers can be formed.

The porous base material layer 4A has a shutdown function, and for example, a polyolefin film such as polyethylene (PE) or polypropylene (PP), or a porous film made of a mixture of these polyolefin resins can be used. Those having a melting point of 135 ° C. or higher can be suitably used.
The polyolefin resin exhibits a shutdown function that blocks the opening near the melting point, thereby interrupting the current.

  On the other hand, as described above, the porous heat-resistant resin layer 4B is made of a heat-resistant resin at 100 ° C., more preferably at 150 ° C. or higher, and even if the porous base material layer 4A reaches a temperature higher than the melting point, it is greatly increased. It has a function of preventing the overall shrink as the separator 4 without causing shrinkage.

The resin material constituting the porous heat-resistant resin layer 4B is preferably one having a glass transition temperature as high as possible from the viewpoint of dimensional stability in a high temperature atmosphere, and can reduce dimensional change and shrinkage due to flow. Therefore, a resin having a melting entropy and no melting point can be preferably used.
Examples of such a resin include polyamides having an aromatic skeleton (for example, aramid), polymers having an aromatic skeleton and having an imide bond (for example, polyimide), and monomers constituting these polymers. A copolymer (for example, polyamideimide) can be mentioned.

In the production of the separator 4 having the above structure, for example, a heat-resistant resin powder as described above is put into a polar organic solvent in which a chloride such as lithium chloride is dissolved in advance, for example, N-methyl-pyrrolidone, A solution dissolved by stirring was prepared, and this solution was applied on the porous film to be the base layer 4A using a desktop coater or the like, and then immersed in a poor solvent such as water to cause phase separation. Thereafter, the separator 4 having a laminated structure of the porous base material layer 4A and the porous heat-resistant resin layer 4B can be obtained by drying with hot air or the like.
At this time, the above-mentioned chloride is necessary for dissolving the heat-resistant resin in a polar organic solvent such as N-methyl-pyrrolidone, but is eluted in the solvent while being immersed in the poor solvent. Therefore, the chlorine content in the separator can be reduced by adjusting the immersion time. In the present invention, the chlorine content needs to be in the range of 500 to 5000 ppm on a mass basis with respect to the entire separator. is there.

  Below, the manufacturing method of the nonaqueous electrolyte battery by 1st Embodiment of this invention is demonstrated.

In producing the positive electrode 2, first, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone. To make a positive electrode mixture slurry.
Next, this positive electrode mixture slurry is applied to the positive electrode current collector 2 </ b> A, and the solvent is dried. Then, the positive electrode active material layer 2 </ b> B is formed by compression molding using a roll press machine or the like, thereby forming the positive electrode 2.

In order to produce the negative electrode 3, first, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to form a negative electrode. A mixture slurry is obtained.
Next, after applying this negative electrode mixture slurry to the negative electrode current collector 3A and drying the solvent, the negative electrode active material layer 3B is formed by compression molding with a roll press or the like, whereby the negative electrode 3 is obtained.

  Then, the positive electrode lead 13 is attached to the positive electrode current collector 2A by welding or the like, and the negative electrode lead 14 is similarly attached to the negative electrode current collector 3A by welding or the like. Next, the positive electrode 2 and the negative electrode 3 are wound through the separator 4 having the above structure, and the tip of the positive electrode lead 13 is welded to the safety valve mechanism 8 and the tip of the negative electrode lead 14 is welded to the battery can 1. Then, the wound positive electrode 2 and negative electrode 3 are sandwiched between a pair of insulating plates 5 and 6 and housed in the battery can 1.

  Next, an electrolytic solution is injected into the battery can 1 and the separator 4 is impregnated with the electrolytic solution. Next, the battery lid 7, the safety valve mechanism 8 and the heat sensitive resistance element 9 are fixed to the opening end of the battery can 1 by caulking through the gasket 10. As described above, the nonaqueous electrolyte battery according to the first embodiment of the present invention is manufactured.

In the nonaqueous electrolyte battery according to the first embodiment of the present invention, when charging is performed, for example, lithium ions are separated from the positive electrode 2 and are absorbed by the negative electrode 3 through the electrolytic solution. Then, lithium ions are released from the negative electrode 3 and absorbed by the positive electrode 2 through the electrolytic solution.
In the separator 4 used in this battery, the porous base material layer 4A made of a polyolefin-based resin exhibits a shutdown function, and the porous heat-resistant resin layer 4B reduces the amount of shrinkage during overheating, and the chlorine ion Since the content is 10 to 140 ppm of the entire separator and the ion permeability is improved, safety of the battery during overheating is ensured and cycle characteristics are improved.

Next explained is the second embodiment of the invention.
FIG. 4 is a perspective view showing the structure of a nonaqueous electrolyte battery according to the second embodiment of the present invention. As shown in the figure, this non-aqueous electrolyte battery is formed by housing a battery element 30 in an exterior material 37 made of a moisture-proof laminate film and sealing the periphery of the battery element 30 by welding.

  The battery element 30 is provided with a positive electrode lead 32 and a negative electrode lead 33, and these leads are sandwiched between outer packaging materials 37 and pulled out to the outside. A resin piece 34 and a resin piece 35 are coated on both surfaces of the positive electrode lead 32 and the negative electrode lead 33 in order to improve the adhesion to the exterior material 37.

The packaging material 37 has, for example, a stacked structure in which an adhesive layer, a metal layer, and a surface protective layer are sequentially stacked.
Here, the adhesive layer is composed of a polymer film, and examples of the material constituting the polymer film include polypropylene (PP), polyethylene (PE), unstretched polypropylene (CPP), and linear low density polyethylene (LLDPE). And low density polyethylene (LDPE).

A metal layer consists of metal foil, As a material which comprises this metal foil, aluminum (Al) is mentioned, for example. In addition, it is also possible to use metals other than aluminum as a material of this metal foil.
Examples of the material constituting the surface protective layer include nylon (Ny) and polyethylene terephthalate (PET). The surface on the adhesive layer side is a storage surface on the side where the battery element 30 is stored.

For example, as shown in FIG. 5, the battery element 30 includes a strip-shaped negative electrode 43 provided with a gel electrolyte layer 45 on both sides, a separator 44, a strip-shaped positive electrode 42 provided with a gel electrolyte layer 45 on both sides, and a separator. 44 is a wound battery element 30 that is laminated in a longitudinal direction and wound in the longitudinal direction.
Since the separator 44 has a structure including a porous base material layer and a porous heat-resistant resin layer, like the separator 4 shown in the first embodiment, further description is omitted. .

The positive electrode 42 includes a strip-shaped positive electrode current collector 42A and a positive electrode mixture layer 42B formed on both surfaces of the positive electrode current collector 42A. The positive electrode current collector 42A is a metal foil made of, for example, aluminum (Al).
One end of the positive electrode 42 in the longitudinal direction is provided with a positive electrode lead 32 connected by, for example, spot welding or ultrasonic welding. As a material of the positive electrode lead 32, for example, a metal such as aluminum can be used.

The negative electrode 43 includes a strip-shaped negative electrode current collector 43A and a negative electrode mixture layer 43B formed on both surfaces of the negative electrode current collector 43A. As the negative electrode current collector 43A, for example, a metal foil such as a copper (Cu) foil, a nickel foil, or a stainless steel foil is used.
Further, similarly to the positive electrode 42, a negative electrode lead 33 connected by, for example, spot welding or ultrasonic welding is also provided at one end of the negative electrode 43 in the longitudinal direction. As a material of the negative electrode lead 33, for example, copper (Cu), nickel (Ni) or the like can be used.

Since the components other than the gel electrolyte layer 45 are the same as those in the first embodiment described above, this will be described.
The gel electrolyte layer 45 includes an electrolytic solution and a polymer compound serving as a holding body that holds the electrolytic solution, and has a so-called gel shape. The gel electrolyte layer 45 is preferable because it can obtain high ionic conductivity and prevent battery leakage. The configuration of the electrolytic solution is the same as that of the first embodiment.

  Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, or polycarbonate. In particular, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable from the viewpoint of electrochemical stability.

The method for manufacturing the nonaqueous electrolyte battery according to the second embodiment of the present invention will be described below.
First, a precursor solution containing a solvent, an electrolyte salt, a polymer compound, and a mixed solvent is applied to each of the positive electrode 42 and the negative electrode 43, and the mixed solvent is volatilized to form the gel electrolyte layer 45. The positive electrode lead 32 is attached to the end of the positive electrode current collector 42A in advance by welding, and the negative electrode lead 33 is attached to the end of the negative electrode current collector 43A in advance by welding.

Next, the positive electrode 42 and the negative electrode 43 on which the gel electrolyte layer 45 is formed are laminated via a separator 44 to form a laminated body, and then the laminated body is wound in the longitudinal direction to obtain a wound battery element. 30 is formed.
Then, a recess 36 is formed by deep drawing the exterior material 37 made of a laminate film, the battery element 30 is inserted into the recess 36, and an unprocessed portion of the exterior material 37 is folded back to the upper portion of the recess 36. The outer periphery is thermally welded and sealed. As described above, the nonaqueous electrolyte battery according to the second embodiment of the present invention is manufactured.

  Also in the nonaqueous electrolyte battery according to the second embodiment, the separator 44 having the same structure and chlorine content as the separator shown in FIG. 3 is used, which is the same as that of the first embodiment. The effect of can be obtained.

  Hereinafter, the present invention will be described in more detail based on examples. The present invention is not limited to these examples.

(1) Examples 1-5, Comparative Examples 1-5
<Preparation of separator>
A solution in which 26 g of lithium chloride is dissolved in 1 liter of N-methyl-pyrrolidone (hereinafter abbreviated as “NMP”) is heated to about 40 ° C., and after adding meta-aramid resin powder or polyimide powder. And dissolved by stirring.

Next, a meta-aramid solution or a polyimide solution using the above-described lithium chloride-added NMP as a solvent is applied on a porous polyethylene (PE) film to be the porous substrate layer 4A with a coater, and any of these solutions is applied. The PE film thus obtained is immersed in a water bath to separate the resin of the coating layer, and then dried with hot air. As shown in FIG. 3B, the porous substrate layer 4A made of porous PE A separator 4 in which a porous heat-resistant resin layer 4B made of aramid or polyimide was disposed on both sides was prepared.
At this time, the coating amount of the heat-resistant resin solution on the porous PE film was applied so that the area density of the porous heat-resistant resin layer 4B on each surface was 0.20 g / cm ² .

  Then, by adjusting the immersion time in the water bath of the PE film coated with the heat-resistant resin solution, the residual amount of chlorine ions caused by lithium chloride contained in each separator is adjusted, and the chlorine contents are different from each other. The separator of Examples 1-5 and Comparative Examples 1-4 and the separator of Comparative Example 5 consisting only of the porous PE film were obtained without applying the heat resistant resin solution.

<Evaluation of separator>
About the separator concerning each Example and comparative example obtained by the above, chlorine content and area shrinkage rate were calculated | required by the following point.
That is, with respect to the chlorine content, a certain amount of each separator was sampled, placed in a flask in which oxygen was blown, and burned. Chlorine was quantified by an ion chromatography method and converted to the chlorine content of the separator.

As for the area shrinkage rate of the separator, first, a sample of longitudinal direction (MD) × width direction (TD) = 50 mm × 50 mm is cut out from each separator, and two points are marked at intervals of 40 mm along the centers in both directions. To do. Then, the separator sample was placed in a thermostatic bath previously maintained at 250 ° C. in a state of being placed (not fixed) on the polytetrafluoroethylene plate, taken out after 20 minutes, and marked in advance. The space | interval between each was measured with calipers, and the area shrinkage rate was calculated by the following formula.
Area shrinkage rate (%) = 100 − [{(interval at two points in the longitudinal direction after heating × interval at two points in the width direction after heating) / (40 mm × 40 mm)} × 100]

<Battery performance evaluation>
An 18650 size cylindrical battery including the separators according to the above examples and comparative examples, a positive electrode made of LiCoO ₂ , and a negative electrode made of graphite was produced.
Then, each cylindrical battery was charged at 4.2V for 3 hours and charged for 3 hours, and then discharged at 3V cutoff at 2 hours to obtain the initial battery capacity.

Also, after attaching a thermocouple to the body of the cylindrical battery produced using each separator with a tape, leave it in a tilted state, and measure the voltage until the internal short circuit occurs. A crushing test was carried out by crushing the battery with a round bar, and the heat generation rate of the battery after an internal short circuit occurred was measured by a thermocouple installed on the surface of the battery can.
These results are shown in Table 1.

  As shown in the results of Table 1, on a porous polyethylene film, in a separator provided with a porous layer made of a heat resistant resin such as aramid or polyimide, by controlling the chlorine content to 500 to 5000 ppm, It was confirmed that the heat generation rate during the crush test can be suppressed while maintaining the initial capacity.

It is a longitudinal cross-sectional view which shows 1st Embodiment of the lithium ion secondary battery of this invention. FIG. 2 is a partially enlarged cross-sectional view of a wound electrode body shown in FIG. 1. It is a partial expanded sectional view of the separator shown in FIG.1 and FIG.2. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the lithium ion secondary battery of this invention. It is a partial expanded sectional view of the battery element shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery can, 2 ... Positive electrode, 2A ... Positive electrode collector, 2B ... Positive electrode mixture layer, 3A ... Negative electrode collector, 3B ... Negative electrode mixture layer, 3 ... Negative electrode, 4 ... Separator, 4A ... Porous group Material layer, 4B ... Porous heat resistant resin layer, 5, 6 ... Insulating plate, 7 ... Battery cover, 8 ... Safety valve mechanism, 10 ... Gasket, 11 ... Disc plate, 12 ... Center pin, 13 ... Positive electrode lead, 14 ... Negative electrode Lead, 20 ... Winding electrode body, 30 ... Battery element, 32 ... Positive electrode lead, 33 ... Negative electrode lead, 34, 35 ... Resin piece, 36 ... Recess, 37 ... Exterior material, 42 ... Positive electrode, 42A ... Positive electrode current collector 42B ... positive electrode mixture layer, 43 ... negative electrode, 43A ... negative electrode current collector, 43B ... negative electrode mixture layer, 44 ... separator, 45 ... gel electrolyte layer.

Claims (4)

A separator comprising a porous base material layer having a shutdown function and a porous heat-resistant resin layer,
The separator characterized by the chlorine content with respect to the whole separator being 500-5000 ppm on a mass basis.   The porous substrate layer is made of a polyolefin-based resin, and the porous heat-resistant resin layer is made of at least one resin selected from the group consisting of polyamide, polyimide, and polyamideimide. Separator. A battery having a positive electrode, a negative electrode, an electrolyte, and a separator,
A battery, wherein the separator comprises a porous base material layer having a shutdown function and a porous heat-resistant resin layer, and a chlorine content with respect to the whole separator is 500 to 5000 ppm on a mass basis.   The battery according to claim 3, wherein an open circuit voltage per unit cell in a fully charged state is 4.2 to 4.6V.

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