JP2010262939A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator with a heat-resisting insulating layer for attaining a nonaqueous electrolyte secondary battery which is excellent on both safety and high-temperature cycle characteristics in overheating even when used charge upper limit voltage is set up at a high level in a nonaqueous electrolyte secondary battery. <P>SOLUTION: The separator 14 with a heat-resisting insulating layer includes a polyolefin layer 14A, and the heat-resisting insulating layer 14B including a heat-resistant resin and oxidation-resistant ceramic particles on its one side or both sides. The nonaqueous electrolyte secondary battery includes a positive electrode 11, a negative electrode 12, the separator with a heat-resisting insulating layer, and a nonaqueous electrolyte, and an open circuit voltage at a full-charged state per a pair of the positive electrode and the negative electrode is set up to be 4.25-4.55 V. The heat-resisting insulating layer includes the oxidation-resistant ceramic particles at a ratio of 80-90%, and is arranged between at least the positive electrode and the polyolefin layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a nonaqueous electrolyte secondary battery including a separator with a heat resistant insulation layer, more particularly, a polyolefin layer and a heat-resistant insulating layer formed by the oxidation-resistant ceramic particles to the heat resistant resin is contained at a predetermined ratio DOO relates to a nonaqueous electrolyte secondary battery using a heat-resistant insulating layer-separators comprise.

In recent years, with the widespread use of portable information electronic devices such as mobile phones, video cameras, and notebook personal computers, these devices have been improved in performance, size, and weight.
Disposable primary batteries and reusable secondary batteries are used as the power source for these devices. However, the secondary balance is high due to the high balance of performance, size, weight, and economy. There is an increasing demand for batteries, particularly lithium ion secondary batteries.
In addition, these devices are being further improved in performance and size, and high energy density is also demanded for lithium ion secondary batteries.

In connection with this, the capacity | capacitance of a lithium ion secondary battery is advanced by improvement and change of an electrode material, and also improvement of a battery structure.
Among them, as one of the techniques for increasing the capacity, the use charge upper limit voltage (open circuit voltage in a fully charged state per pair of positive electrode and negative electrode) (hereinafter abbreviated as “use charge upper limit voltage”) is increased. Is attracting attention.
A conventional lithium ion secondary battery uses lithium cobaltate for the positive electrode and a carbon material for the negative electrode, and the upper limit voltage for use is 4.1 to 4.2V. Thus, in the lithium ion secondary battery in which the use upper limit voltage is designed, the positive electrode active material such as lithium cobaltate used for the positive electrode utilizes a capacity of about 50 to 60% with respect to its theoretical capacity. Not too much.
For this reason, it is possible in principle to utilize the remaining capacity by further increasing the use charge upper limit voltage.
In fact, it is known that a higher energy density can be achieved by setting the use charge upper limit voltage to 4.25 V or more (see Patent Document 1).

In addition, since the energy density of a lithium ion secondary battery increases as its capacity increases, the demand for improved reliability when a large amount of energy is released in an overheating test or an internal short circuit test has become extremely large. .
For this reason, there is a strong demand for a lithium ion secondary battery that achieves both high reliability and high capacity for such tests.

A general lithium ion secondary battery includes a positive electrode including a lithium composite oxide, a negative electrode including a material capable of inserting and extracting lithium ions, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. And a positive electrode and a negative electrode are wound with a separator interposed therebetween to constitute a columnar electrode plate group.
The separator has a role of electrically insulating the positive electrode and the negative electrode and a role of holding the non-aqueous electrolyte. As a separator for such a lithium ion secondary battery, a polyolefin microporous membrane is generally used.
This is because when an abnormally large current flows due to an external short circuit or a minute internal short circuit of a lithium ion secondary battery, the battery temperature rises significantly and flammable gas is generated. In order to prevent rupture or ignition, the polyolefin microporous membrane contracts or melts due to its heat, and is considered to have a function (shutdown function) that blocks micropores and blocks ion permeation. Because.

However, even if the shutdown function works, when the temperature of the lithium ion secondary battery further rises, the separator melts and heat shrinks, causing a large-scale short circuit between the positive electrode and the negative electrode, so-called meltdown occurs. There's a problem.
Further, if the thermal meltability of the separator is increased in order to improve the shutdown function, there is a problem that the meltdown temperature of the separator is lowered.

  Therefore, in order to improve both shutdown property and meltdown resistance, for example, a base material layer including a porous film, a heat-resistant nitrogen-containing aromatic polymer such as aromatic polyamide and polyimide, and ceramic powder A separator composed of a layer containing benzene has been proposed (see Patent Document 2).

International Publication No. 03/019713 Pamphlet Japanese Patent No. 3175730

  However, in the lithium ion secondary battery to which the separator described in Patent Document 2 is applied, when the upper limit voltage for use is set, an internal short circuit or the like during overheating can be suppressed, but sufficient performance in high-temperature cycle characteristics. There was a problem that could not be obtained.

The present invention has been made in view of such problems of the prior art, and the object of the present invention is to provide safety during overheating and a high-temperature cycle even when the use charge upper limit voltage is set high. and to provide a nonaqueous electrolyte secondary battery using a heat-insulating layer-separators both can provide excellent non-aqueous electrolyte secondary battery characteristics.

  As a result of intensive investigations to achieve the above object, the present inventors formed a heat-resistant insulating layer comprising one or both surfaces of a polyolefin layer containing a heat-resistant resin and oxidation-resistant ceramic particles in a predetermined ratio. Thus, a separator with a heat-resistant insulating layer was produced, and it was found that the above-described object can be achieved by applying the separator, thereby completing the present invention.

That is, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode formed by forming a positive electrode mixture layer containing a positive electrode active material on a positive electrode current collector, and a negative electrode formed by forming a negative electrode mixture layer on a negative electrode current collector. And a separator with a heat-resistant insulating layer and a non-aqueous electrolyte, and the open circuit voltage in a fully charged state per pair of positive electrode and negative electrode is 4.25 to 4.35V.
Further, in the nonaqueous electrolyte secondary battery of the present invention, such a separator with a heat-resistant insulating layer is formed on a polyolefin layer and one or both surfaces of this polyolefin layer, and contains a heat-resistant resin and oxidation-resistant ceramic particles. And an insulating layer.
Furthermore, in the nonaqueous electrolyte secondary battery of the present invention, the heat-resistant insulating layer contains the oxidation-resistant ceramic particles in a proportion of 80 to 90%, and the heat-resistant insulating layer is between the positive electrode and the polyolefin layer. It is arranged.
The heat-resistant insulating layer contains the oxidation-resistant ceramic particles in a proportion of 80 to 90%,
The heat resistant resin contains at least an aromatic polyamide, and the heat resistant insulating layer comprises the positive electrode and the polyolefin.
Between the layers.

In a preferred embodiment of the nonaqueous electrolyte secondary battery of the present invention, the oxidation-resistant ceramic particles contain at least alumina.

  In a preferred embodiment of the nonaqueous electrolyte secondary battery of the present invention, the ratio of the surface density of the positive electrode mixture layer to the surface density of the negative electrode mixture layer is 1.90 to 2.10.

  Furthermore, in another preferred embodiment of the non-aqueous electrolyte secondary battery of the present invention, the positive electrode active material covers at least all or part of the surface of lithium cobalt oxide with an oxide containing one or both of nickel and manganese. The positive electrode active material.

  According to the present invention, a separator with a heat-resistant insulating layer is formed by forming a heat-resistant insulating layer comprising a heat-resistant resin containing oxidation-resistant ceramic particles in a predetermined ratio on one or both surfaces of a polyolefin layer. A separator with a heat-resistant insulating layer that can realize a non-aqueous electrolyte secondary battery that is excellent in both safety and high-temperature cycle characteristics even when the upper limit voltage for charging is set high because it is applied. And a non-aqueous electrolyte secondary battery using the same.

It is one Embodiment of the nonaqueous electrolyte secondary battery of this invention, Comprising: It is sectional drawing which shows an example of a cylindrical secondary battery. It is sectional drawing which expands and shows a part of winding electrode body in the cylindrical secondary battery shown in FIG.

  Hereinafter, embodiments of a separator with a heat-resistant insulating layer and a nonaqueous electrolyte secondary battery according to the present invention will be described in detail with reference to the drawings. In the present specification and claims, “%” for content, concentration, etc. represents mass percentage unless otherwise specified.

FIG. 1 is a cross-sectional view showing an example of a cylindrical secondary battery as an embodiment of the nonaqueous electrolyte secondary battery of the present invention.
As shown in the figure, the secondary battery is a part of an exterior member, and has a battery element 10 inside a substantially hollow cylindrical battery can 1A. In the battery element 10, the positive electrode 11 and the negative electrode 12 are positioned to face each other with a separator 14 with a heat-resistant insulating layer, and contain a non-aqueous electrolyte (not shown).
In addition, as will be described in detail later, the separator 14 with a heat-resistant insulating layer has at least a heat-resistant insulating layer (not shown) of the separator 14 with a heat-resistant insulating layer disposed between the positive electrode 11 and a polyolefin layer (not shown) of the separator 14 with a heat-resistant insulating layer. Built in.
The battery element 10 excluding the nonaqueous electrolyte is referred to as a wound electrode body 10A.
The strip-shaped positive electrode, negative electrode, and separator with a heat-resistant insulating layer used when producing the wound electrode body 10A have a relationship of, for example, (separator width)> (negative electrode width)> (positive electrode width). Can be used. Such a wound electrode body can prevent the dendrite-like crystal from growing in the negative electrode due to wraparound from the positive electrode, and can also prevent an internal short circuit due to the dendrite-like crystal reaching the positive electrode. .

The battery can 1A is made of, for example, steel plated with nickel, and has one end closed and the other end open. Inside the battery can 1A, insulating plates 2A and 2B are arranged so as to sandwich the battery element 10 from above and below.
In addition, at the open end of the battery can 1A, a battery lid 1B constituting a part of the exterior member, a safety valve mechanism 3 and a heat-sensitive resistance element (Positive Temperature Coefficient; PTC element) provided inside the battery lid 1B 4) is attached by caulking through the gasket 5, and the inside of the battery can 1A is sealed.

  The battery lid 1B is made of the same material as the battery can 1A, for example. The safety valve mechanism 3 is electrically connected to the battery lid 1B via the heat sensitive resistance element 4, and when the internal pressure of the battery exceeds a certain level due to internal short circuit or external heating, the disc plate 3A Is reversed so that the electrical connection between the battery lid 1B and the battery element 10 is cut off. When the temperature rises, the heat sensitive resistance element 4 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current, and is made of, for example, barium titanate semiconductor ceramics. The gasket 5 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The battery element 10 is wound around, for example, the center pin 6. A positive electrode lead 7 made of aluminum or the like is connected to the positive electrode 11 of the battery element 10, and a negative electrode lead 8 made of copper, nickel, stainless steel or the like is connected to the negative electrode 12. The positive electrode lead 7 is electrically connected to the battery lid 1B by being welded to the safety valve mechanism 3, and the negative electrode lead 8 is welded and electrically connected to the battery can 1A.

FIG. 2 is an enlarged cross-sectional view showing a part of a wound electrode body in the cylindrical secondary battery shown in FIG.
As shown in the figure, the wound electrode body 10A includes a positive electrode 11, a negative electrode 12, and a separator 14 with a heat-resistant insulating layer.
Here, the positive electrode 11 has a structure in which a positive electrode mixture layer 11B is coated on both surfaces of a positive electrode current collector 11A having a pair of opposed surfaces. The positive electrode current collector 11A is made of a metal foil such as an aluminum foil. Although not shown in the figure, the positive electrode current collector has a portion exposed without being covered with the positive electrode mixture layer at one end in the longitudinal direction, and the positive electrode lead described above is attached to this exposed portion. Yes.
Similarly to the positive electrode 11, the negative electrode 12 also has a structure in which a negative electrode mixture layer 12B is coated on both surfaces of a negative electrode current collector 12A having a pair of opposing surfaces. The negative electrode current collector 12A is made of a metal foil such as a copper foil, a nickel foil, or a stainless steel foil. Although not shown in the figure, the negative electrode current collector has a portion exposed without being coated with the negative electrode mixture layer at one end in the longitudinal direction, and the negative electrode lead described above is attached to this exposed portion. Yes.
Furthermore, the separator 14 with a heat-resistant insulating layer includes a polyolefin layer 14A and a heat-resistant insulating layer 14B. The heat-resistant insulating layer 14B is disposed at least between the positive electrode 11 and the polyolefin layer 14A.
The heat-resistant insulating layer 14B is disposed at least between the positive electrode 11 and the polyolefin layer 14A. However, the heat-resistant insulating layer 14B is not disposed in the entire region between the positive electrode 11 and the polyolefin layer 14A. If arranged, it is included in the scope of the present invention.
Although not shown, the positive electrode and the negative electrode have a structure in which a positive electrode mixture layer and a negative electrode mixture layer are respectively coated on one side of a positive electrode current collector and a negative electrode current collector having a pair of opposed surfaces. It may be. Further, although not shown, the heat-resistant insulating layer may be disposed not only between the positive electrode and the polyolefin layer but also between the negative electrode and the polyolefin layer. Furthermore, although not shown, the heat-resistant insulating layer may be disposed only on one side of the positive electrode or the negative electrode.

[Positive electrode]
The positive electrode mixture layer 11B includes, for example, a positive electrode material capable of inserting and extracting lithium ions as a positive electrode active material, and may include a conductive agent and a binder as necessary.
Here, the positive electrode active material, the conductive agent, and the binder need only be uniformly dispersed, and the mixing ratio is not limited.

As a positive electrode material capable of inserting and extracting lithium used as a positive electrode active material, for example, a lithium oxide, a lithium phosphorous oxide, a lithium sulfide, or an interlayer containing lithium according to the type of the target battery Lithium-containing compounds such as compounds are suitable, and two or more of these may be mixed and used. In order to increase the energy density, a lithium-containing compound containing lithium, a transition metal element, and oxygen (O) is preferable. Among them, as the transition metal element, cobalt (Co), nickel (Ni), manganese (Mn), and iron It is more preferable if it contains at least one of the group consisting of (Fe).
Examples of such lithium-containing compounds include lithium composite oxides represented by the average composition shown in Formula (1) or Formula (2).

Li _a Co _(1-b) M1 _b O _(2-c) (1)
(In the formula, M1 represents vanadium (V), copper (Cu), zirconium (Zr), zinc (Zn), magnesium (Mg), aluminum (Al), gallium (Ga), yttrium (Y) and iron (Fe A, b, and c are in a range of 0.9 ≦ a ≦ 1.1, 0 ≦ b ≦ 0.3, and −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 d Ni e Co f Mn g} M2 (1-efg) O (2-h) ... (2)
(In the formula, M2 represents vanadium (V), copper (Cu), zirconium (Zr), zinc (Zn), magnesium (Mg), aluminum (Al), gallium (Ga), yttrium (Y) and iron (Fe And d, e, f, g and h are 0.9 ≦ d ≦ 1.1, 0 <e <1, 0 <f <1, 0 <g <. The values are within the ranges of 0.5, 0 ≦ 1-e−fg, −0.1 ≦ h ≦ 0.1 Note that the composition of lithium varies depending on the state of charge and discharge, and the value of d is completely (The value in the discharge state is shown.)

Furthermore, as the lithium-containing compound, for example, a lithium composite oxide having a spinel structure represented by the average composition represented by the formula (3), or an olivine type represented by the average composition represented by the formula (4) And lithium composite phosphate having the structure: Specific examples include Li _i Mn ₂ O ₄ (i≈1) and Li _j FePO ₄ (j≈1).

Li _k Mn _2-l M3 _l O _m F _n (3)
(Wherein M3 is cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe ), Copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). l, m, and n are values within the range of 0.9 ≦ k ≦ 1.1, 0 ≦ l ≦ 0.6, 3.7 ≦ m ≦ 4.1, and 0 ≦ n ≦ 0.1. Note that the composition of lithium varies depending on the state of charge and discharge, and the value of k represents the value in a fully discharged state.)

Li _o M4PO ₄ (4)
(Wherein M4 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). O is a value within a range of 0.9 ≦ o ≦ 1.1, and the composition of lithium varies depending on the state of charge and discharge, and the value of o represents a value in a fully discharged state. )

As the positive electrode material capable of inserting and extracting lithium used as the positive electrode active material, in addition to the above-described positive electrode material, for example, lithium such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , NiS, and MoS Inorganic compounds that do not contain any of them.

Among them, a positive electrode active material in which different elements such as aluminum (Al), magnesium (Mg), zirconium (Zr), and titanium (Ti) are dissolved, a positive electrode active material containing a lithium nickel manganese composite oxide, cobalt acid, etc. A positive electrode active material in which the surface of lithium is covered with a lithium manganate having a spinel structure or a nickel cobalt composite oxide is preferable from the viewpoint of having a stable structure even at a high charging voltage.
In addition, from the viewpoint that higher electrode filling properties and cycle characteristics can be obtained, the surface of the core particle made of any one of the lithium-containing compounds represented by formulas (1) to (4) is made more than any other lithium-containing compound. The composite particles may be coated with fine particles. Furthermore, the composite particle which coat | covered all or one part of the surface of lithium cobaltate with the oxide containing at least one of nickel and manganese can also be used. Such an oxide may or may not form a composite oxide with lithium cobalt oxide.

  As the conductive agent, for example, a carbon material such as acetylene black, graphite, or ketjen black can be used.

  Further, as the binder, for example, a polyvinylidene fluoride or a copolymer of vinylidene fluoride or a modified product thereof, a fluorocarbon resin such as polytetrafluoroethylene or a copolymer of polytetrafluoroethylene, polyacrylonitrile, poly An acrylic resin such as an acrylic ester can be used. In particular, vinylidene fluoride is preferable because it is excellent in durability, particularly swelling resistance.

More specifically, examples of the vinylidene fluoride copolymer include a vinylidene fluoride-hexafluoropropylene copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, and a vinylidene fluoride-chlorotrifluoroethylene copolymer. And vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer.
Moreover, what copolymerized other ethylenically unsaturated monomer to the copolymer illustrated above can be mentioned.
More specific examples of the copolymerizable ethylenically unsaturated monomer include acrylic acid ester, methacrylic acid ester, vinyl acetate, acrylonitrile, acrylic acid, methacrylic acid, maleic anhydride, butadiene, styrene, and N-vinyl. Pyrrolidone, N-vinyl pyridine, glycidyl methacrylate, hydroxyethyl methacrylate, methyl vinyl ether and the like can be mentioned.

Such a binder may be used individually by 1 type, and multiple types may be mixed and used for it.
Moreover, as content in the positive mix layer of a binder, Preferably it exists in the range of 0.5-7%, More preferably, it exists in the range of 1.2-4%. This is because when the content of the binder is small, the binding property is not sufficient, and it becomes difficult to bind the positive electrode active material or the like to the positive electrode current collector. Moreover, when there is much content of a binder, it is because a binder with low electronic conductivity and ion conductivity coat | covers a positive electrode active material, and charge / discharge efficiency may fall.

[Negative electrode]
The negative electrode mixture layer 12B includes any one or two or more negative electrode materials capable of inserting and extracting lithium ions as a negative electrode active material, and, as necessary, the negative electrode mixture layer. In addition, a conductive agent and a binder may be included. Furthermore, other materials that do not contribute to charging, such as a viscosity modifier, may be included.
Here, for example, the negative electrode active material, the conductive agent, and the binder need only be uniformly dispersed, and the mixing ratio is not limited.

Examples of negative electrode materials capable of inserting and extracting lithium include non-graphitizable carbon, graphitizable carbon, natural or artificial graphite, pyrolytic carbons, cokes, glassy carbons, and organic polymer compounds. Examples thereof include carbon materials such as fired bodies, carbon fibers, and activated carbon.
Here, examples of the 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. Some are classified as sex carbon.
These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and 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, a material having a low charge / discharge potential, specifically, a material having a charge / discharge potential close to that of lithium metal is preferable because a high energy density of the battery can be easily realized.

When a carbon material is used as the negative electrode material, the ratio of the surface density of the positive electrode mixture layer of the positive electrode to the surface density of the negative electrode mixture layer of the negative electrode (positive electrode mixture layer area density / negative electrode mixture layer area density) is: It is preferably in the range of 1.90 to 2.10. This is because when the mixture layer surface density ratio is larger than 2.10, metallic lithium may be deposited on the surface of the negative electrode, and charge / discharge efficiency and safety may be lowered. Moreover, if the mixture layer surface density ratio is smaller than 1.90, the negative electrode material not involved in the reaction with lithium (Li) as the electrode reactant increases, and the energy density may decrease. is there.
In addition, this secondary battery is designed such that the open circuit voltage (that is, the upper limit voltage for use of the battery) during full charge is in the range of 4.25 to 4.55V. Therefore, even if the same positive electrode active material is used in a battery having an open circuit voltage of 4.20 V during full charge, the amount of lithium released per unit mass is increased. Further, the amounts of the positive electrode active material and the negative electrode active material are adjusted accordingly, whereby a high energy density can be obtained. In particular, when the open circuit voltage at the time of complete charging is in the range of 4.35V to 4.45V, the effect that can be practically used is high.

Further, as another negative electrode material capable of inserting and extracting lithium, a material which can store and release lithium and includes at least one of a metal element and a metalloid element as a constituent element is used. Can be mentioned. This is because a high energy density can be obtained by using such a material. In particular, the use with a carbon material is more preferable 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, or may have at least a part of one or more of these phases. Note that in this specification, 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. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of the metal element or metalloid element constituting the 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) can be mentioned. These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or metalloid element as a constituent element in the short-period type periodic table is preferable, and at least one of silicon (Si) and tin (Sn) is particularly preferable. It is included as an element. This is because silicon (Si) and tin (Sn) have a large ability to occlude and release lithium (Li), and a high energy density can be obtained.

  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 ( Mn), zinc (Zn), indium (In), silver (Ag), titanium (Ti), germanium (Ge), bismuth (Bi), antimony (Sb) and chromium (Cr). Mention may be made of seeds. 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), Of the group consisting of manganese (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 can be mentioned.

  Examples of the tin (Sn) compound or silicon (Si) compound include those containing oxygen (O) or carbon (C), for example, in addition to tin (Sn) or silicon (Si). The second constituent element may be included.

Furthermore, other metal compounds or polymer materials can be cited as still another negative electrode material capable of inserting and extracting lithium. 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 . Examples of other polymer materials include polyacetylene, polyaniline, and polypyrrole.

Examples of the conductive agent include graphites such as artificial graphite and expanded graphite, carbon blacks such as acetylene black, ketjen black, channel black and furnace black, conductive fibers such as carbon fiber and metal fiber, copper Examples thereof include metal powders such as powder or nickel powder, and organic conductive materials such as polyphenylene derivatives, among which acetylene black, ketjen black, or carbon fiber is preferable.
The content of the conductive agent is preferably in the range of 0.1 to 30 parts by mass with respect to 100 parts by mass of the negative electrode material, and more preferably in the range of 0.5 to 10 parts by mass. As the conductive agent, one kind may be used alone, or a plurality of kinds may be mixed and used.

Furthermore, examples of the binder include polytetrafluoroethylene and polyvinylidene fluoride, and one kind may be used alone, or a plurality kinds may be mixed and used.
Furthermore, examples of the viscosity modifier include carboxymethyl cellulose.

[Separator with heat-resistant insulating layer]
The separator 14 with a heat-resistant insulating layer separates the positive electrode 11 and the negative electrode 12 and allows lithium ions to pass while preventing a short circuit of current due to contact between both electrodes. The separator layer 14A and the heat-resistant insulating layer 14B are separated from each other. Prepare.

  The polyolefin layer 14A is a porous film made of a polyolefin-based synthetic resin such as polypropylene or polyethylene, and has a large ion permeability and an insulating thin film having a predetermined mechanical strength. Moreover, it is good also as a structure which laminated | stacked these 2 or more types of porous membranes. Those containing a polyolefin-based porous membrane are excellent in the separation between the positive electrode and the negative electrode, and can further reduce internal short circuit and open circuit voltage drop.

The heat resistant insulating layer 14B contains a heat resistant resin and ceramic particles.
The heat-resistant insulating layer only needs to be disposed at least between the positive electrode and the polyolefin layer as described above. As such a heat-resistant insulating layer, a mixture of a heat-resistant resin and oxidation-resistant ceramic particles is used. Examples thereof include those formed in layers and those formed in layers.

  In the present specification and claims, the heat-resistant resin is a polymer containing a nitrogen atom and an aromatic ring in the main chain, for example, an aromatic polyamide (hereinafter sometimes referred to as “aramid”), An aromatic polyimide (hereinafter sometimes referred to as “polyimide”), an aromatic polyamideimide, and the like can be given.

Examples of the aramid include meta-oriented aromatic polyamide (hereinafter sometimes referred to as “meta-aramid”) and para-oriented aromatic polyamide (hereinafter sometimes referred to as “para-aramid”). Para-aramid is preferable in that it easily becomes.
Here, para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4, 4'-biphenylene, 1,5-naphthalene, 2,6-naphthalene, and the like, which are substantially composed of repeating units bonded in the opposite direction).
Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide), poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic acid amide), poly ( Para-aligned or para-oriented such as paraphenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer Examples include para-aramid having a structure according to the type.

Para-aramid can be dissolved in a polar organic solvent to form a low-viscosity solution and has excellent coating properties. It is preferably 7 to 2.5 dl / g.
If the intrinsic viscosity is less than 1.0 dl / g, sufficient film strength may not be obtained. On the other hand, if the intrinsic viscosity exceeds 2.8 dl / g, it may be difficult to form a stable para-aramid solution, and para-aramid may be deposited, making it difficult to form a film.
Examples of the polar organic solvent include a polar amide solvent or a polar urea solvent, specifically, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, Although tetramethyl urea etc. can be mentioned, it is not limited to these.

  Para-aramid is porous and is preferably a fibrillated polymer. Such a fibrillar polymer is microscopically non-woven, has a layered and porous void, and forms a so-called para-aramid porous resin.

On the other hand, as the polyimide, for example, a wholly aromatic polyimide produced by condensation polymerization of an aromatic dianhydride and a diamine is preferable.
Specific examples of the dianhydride include pyromellitic dianhydride, 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic Examples thereof include acid dianhydride, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, and the like.
Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenonediamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, , 5'-naphthalenediamine and the like. However, the present invention is not limited to these.

Moreover, when creating a porous film directly from a polyimide solution, the polyimide soluble in a solvent can be used conveniently. An example of such a polyimide is a polyimide that is a polycondensate of 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine.
As a polar organic solvent used for polyimide, dimethyl sulfoxide, cresol, o-chlorophenol, or the like can be suitably used in addition to those exemplified in the case of the aramid.

  Furthermore, the polyimide is preferably porous. For example, a solid film can be perforated by machining or laser processing to make it porous. Moreover, when producing a polyimide film by the solution casting method, a porous film can be produced by controlling polyimide molding conditions such as polymer concentration during coating. Furthermore, by combining the ceramic powder, a uniform and fine porous structure can be formed with a solution having an arbitrary polymer concentration. Furthermore, the air permeability can be controlled by the content of the ceramic powder.

The heat-resistant insulating layer contains oxidation-resistant ceramic particles in a proportion of 60 to 90%, and preferably contains 65 to 85%.
In addition, when the content of the oxidation-resistant ceramic particles is less than 60%, deterioration in the high charge range may not be suppressed. When it exceeds 90%, the separator becomes brittle and handling becomes difficult. There is.

Examples of the oxidation resistant ceramic particles include ceramic particles made of an electrically insulating metal oxide, metal nitride, metal carbide and the like. For example, alumina, silica, titanium dioxide, zirconium oxide or the like can be preferably used. These particles may be used alone or in combination of two or more.
Further, the shape of the oxidation-resistant ceramic particles is not particularly limited, and spherical or random shapes can be used.
Furthermore, the oxidation-resistant ceramic particles preferably have an average primary particle size of 1.0 μm or less and 0.5 μm or less from the viewpoint of the effect on the strength of the separator and the smoothness of the coated surface. More preferably, it is 0.1 μm or less. The average particle size of such primary particles can be measured by a method of analyzing a photograph obtained with an electron microscope with a particle size measuring instrument.
When the average particle size of the primary particles of the oxidation-resistant ceramic particles exceeds 1.0 μm, the separator becomes brittle and the coated surface may become rough.
Such an oxidation-resistant ceramic particle, for example, when a mixture of a heat-resistant resin and an oxidation-resistant ceramic particle is formed in a layered form, is entangled with the heat-resistant resin and captured, and is wholly or partially in the separator. Included in a distributed manner.

The separator with a heat-resistant insulating layer may further have a base material layer. Examples of such a base material layer include a porous woven fabric, non-woven fabric, paper or the like made of electrically insulating organic, inorganic fibers or pulp. A porous film can be mentioned. Among these, a nonwoven fabric, paper, or a porous film is preferable from the viewpoint of cost and thinness.
Specifically, examples of the organic fiber include fibers made of a thermoplastic polymer such as rayon, vinylon, polyester, acrylic, polystyrene, nylon, and natural fibers such as manila hemp. Examples of inorganic fibers include glass fibers and alumina fibers.
Moreover, the weight per unit area of the separator with a heat resistant insulating layer is preferably 40 g / m ² or less, and more preferably 15 g / m ² or less.
Further, the porosity of the separator with a heat-resistant insulating layer is determined by electron and ion permeability, material, or thickness, but is generally in the range of 30 to 80%, more preferably in the range of 35 to 50%. Is within. This is because if the porosity is low, the ion conductivity is lowered, and if the porosity is high, a short circuit may occur.
Furthermore, the thickness of the separator with a heat-resistant insulating layer is, for example, preferably in the range of 10 to 300 μm, more preferably in the range of 15 to 70 μm, and still more preferably in the range of 15 to 25 μm. This is because if the thickness of the separator with the heat-resistant insulating layer is small, a short circuit may occur, and if the thickness is large, the filling amount of the positive electrode material decreases.

The separator with a heat-resistant insulating layer preferably contains 10% or more of a thermoplastic polymer that melts at 260 ° C. or less, more preferably contains 30% or more, and contains 40% or more. More preferably.
Such a thermoplastic polymer melts when the temperature rises and can close the voids of the separator with the heat-resistant insulating layer. Such a thermoplastic polymer, when used as a separator of a lithium ion secondary battery, is preferably a polymer that melts at 260 ° C. or less, more preferably 200 ° C. or less, from the viewpoint of a shutdown function. Moreover, since the melting temperature is appropriate as the shutdown temperature, it is preferably about 100 ° C. or higher.
Examples of such thermoplastic polymers include polyolefin resins, acrylic resins, styrene resins, polyester resins, and nylon resins.
In particular, polyethylene such as low density polyethylene, high density polyethylene and linear polyethylene, or their low molecular weight wax content, or polyolefin resin such as polypropylene is suitable because it has an appropriate melting temperature and is easily available. These may be used alone or in combination of two or more.

[Nonaqueous electrolyte]
The nonaqueous electrolyte is contained in, for example, all or part of the separator 14 with the heat-resistant insulating layer, the positive electrode mixture layer 11B, and the negative electrode mixture layer 12B described above. As such a non-aqueous electrolyte, for example, a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent can be used.

As the electrolyte salt, it is preferable to use those terms of high ionic conductivity of the electrolyte solution is obtained, for example, include lithium hexafluorophosphate (LiPF _6).

The concentration of lithium hexafluorophosphate (LiPF ₆ ) is preferably in the range of 0.1 to 2.0 mol / kg in the electrolytic solution. This is because the ion conductivity can be further increased within this range.

As the electrolyte salt, another electrolyte salt may be further mixed and used. Examples of other electrolyte salts include LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ), LiN (SO ₂ CF ₃ ) (SO ₂ C ₃ F ₇ ), LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ) , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBr, and the like. Other electrolyte salts may be used alone or in combination of two or more.

The electrolyte salt may include an organic lithium salt in which an electron-withdrawing organic substituent such as a carbonyl group or a sulfonyl group is bonded to a boron (B) atom serving as an anion center via an oxygen atom. Good.
Specific examples of the organic lithium salt in which an electron-withdrawing organic substituent such as a carbonyl group or a sulfonyl group is bonded to a boron (B) atom serving as an anion center via an oxygen atom are as follows. be able to.
The group IIIb to group Vb atoms that are the anion centers may be any of B (boron), N (nitrogen), P (phosphorus), Ga (gallium), Al (aluminum), Si (silicon), and the like. In view of the number of bonds, the group IIIb to group IVb atoms are preferable, and the group IIIb atom is particularly preferable. B (boron) is most suitable as the atom serving as the anion center. In other words, boron (B) has a small atomic weight of 10.8, and as an element contained in an organic substance, four bonds more than oxygen (O) and nitrogen (N) are possible. This is because it has the ability to bind to an organic substituent having many electron withdrawing properties.
An oxygen atom is interposed between the anion-centered atom and the electron-withdrawing organic substituent directly, and the oxygen atom has a high electronegativity. In addition, since only two bonds are present for stabilization, an electron-withdrawing organic substituent can be bound in a state with little steric hindrance. And the electron-withdrawing organic substituent attracts electrons to the anion-centered atom through an oxygen atom, lowers the electron density of the anion-centered atom, and makes it difficult to take out the electron from the anion-center. Prevents the anion from being oxidized.
Examples of the electron-withdrawing organic substituent include a carbonyl group, a sulfonyl group, an amino group, a cyano group, and a halogenated alkyl group, and are particularly suitable because a carbonyl group and a sulfonyl group can be easily synthesized.

Specific examples of the organic lithium salt include those represented by the following formulas (5) and (6).
LiBXX '(5)
LiBF ₂ X (6)
(In the formula, X and X ′ are electron-withdrawing organic substituents having oxygen bonded to a boron (B) atom. For example, X and X ′ are each independently —O—C (= O)-(CRR ′) _n —C (═O) —O—, —O—S (═O) —O— (CRR ′) _n —O—S (═O) —O—, R and R ′ independently represents an alkyl group, a hydrogen atom (H), a halogen atom (F, Cl, etc.), and n is an integer from 0 to 5.)

  Further, as other organic lithium salts, preferred examples include difluoro [oxolato-O, O ′] lithium borate and lithium bisoxalate borate.

  As the non-aqueous solvent, for example, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used, and it is preferable to use one of ethylene carbonate and propylene carbonate, particularly a mixture of both. This is because the cycle characteristics can be improved.

  Further, as the non-aqueous solvent, in addition to these cyclic carbonates, for example, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and the like are preferably mixed and used. This is because high ionic conductivity can be obtained.

Further, the non-aqueous solvent preferably contains vinylene carbonate or 4-fluoroethylene carbonate. A film can be formed on the negative electrode, and decomposition of ionic metal complexes such as lithium difluoro [oxolato-O, O ′] lithium borate and lithium bisoxalate borate on the negative electrode can be suppressed. It is because it can improve.
The content of vinylene carbonate or 4-fluoroethylene carbonate is preferably in the range of 0.1 to 30% in the non-aqueous electrolyte. This is because if it is less than 0.1%, the effect of improving the cycle characteristics may be reduced, and if it exceeds 30%, it may be excessively decomposed on the negative electrode and the charge / discharge efficiency may be lowered.

Furthermore, other nonaqueous solvents include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 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-dimethyl Examples include imidazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, and trimethyl phosphate.
In addition, a non-aqueous solvent may be used individually by 1 type, and multiple types may be mixed and used for it.

Next, an example of a method for manufacturing the secondary battery described above will be described.
The cylindrical secondary battery described above can be manufactured as follows.
First, the positive electrode 11 is produced. For example, when a particulate positive electrode active material is used, a positive electrode mixture is prepared by mixing the positive electrode active material and, if necessary, a conductive agent and a binder, and a dispersion medium such as N-methyl-2-pyrrolidone. To produce a positive electrode mixture slurry.
Next, this positive electrode mixture slurry is applied to the positive electrode current collector 11A, dried, and compression molded by a roll press or the like to form the positive electrode mixture layer 11B.

  Moreover, the negative electrode 12 is produced. For example, when using a particulate negative electrode active material, a negative electrode active material is mixed with a conductive agent and a binder as necessary to prepare a negative electrode mixture, and N-methyl-2-pyrrolidone, water, etc. A negative electrode mixture slurry is prepared by dispersing in a dispersion medium. Thereafter, this negative electrode mixture slurry is applied to the negative electrode current collector 12A, dried, and compression molded by a roll press or the like to form the negative electrode mixture layer 12B.

  Furthermore, the separator 14 with a heat-resistant insulating layer is produced. First, an inorganic salt for forming micropores is dissolved in a dispersion medium such as N-methyl-2-pyrrolidone, and a heat resistant resin is dissolved therein to obtain a heat resistant resin solution. Next, oxidation-resistant ceramic particles are added to obtain a slurry for forming a heat-resistant insulating layer. Further, the obtained slurry for forming a heat-resistant insulating layer is applied to one side or both sides of the microporous polyolefin resin film to be the polyolefin layer 14A with a doctor blade and dried. Thereafter, the dried film of the heat-resistant insulating layer forming slurry is washed with water, the inorganic salt for forming micropores is removed, and micropores are formed to form the heat-resistant insulating layer 14B. Alternatively, by applying the obtained slurry for forming a heat-resistant insulating layer to one surface or both surfaces of the microporous polyolefin resin film to be the polyolefin layer 14A with a doctor blade or the like and directly touching it in water, The heat-resistant insulating layer 14B may be formed by insolubilizing, washing with water, removing inorganic salts for forming micropores, and forming micropores.

  Next, the positive electrode lead 7 is led out from the positive electrode current collector 11A, and the negative electrode lead 8 is led out from the negative electrode current collector 12A. Thereafter, for example, the positive electrode 11 and the negative electrode 12 are wound through a separator 14 with a heat-resistant insulating layer to form a wound electrode body 20A, the tip of the positive electrode lead 7 is welded to the safety valve mechanism 3, and the negative electrode lead 8 The wound positive electrode 11 and negative electrode 12 are sandwiched between a pair of insulating plates 2A and 2B and housed in the battery can 1A. After the positive electrode 11 and the negative electrode 12 are accommodated in the battery can 1A, a non-aqueous electrolyte (not shown) is injected into the battery can 1A and impregnated in the separator 14 with a heat-resistant insulating layer. Thereafter, the battery lid 1 </ b> B, the safety valve mechanism 3, and the heat sensitive resistance element 4 are fixed to the opening end portion of the battery can 1 </ b> A via a gasket 5. Thereby, the cylindrical secondary battery shown in FIGS. 1 and 2 is completed.

  In the secondary battery described above, when charged, lithium ions are released from the positive electrode mixture layer 11B and occlude and release lithium contained in the negative electrode mixture layer 12B through a non-aqueous electrolyte (not shown). Occluded in possible negative electrode materials. Next, when discharging is performed, lithium ions occluded in the negative electrode material capable of occluding and releasing lithium contained in the negative electrode mixture layer 12B are released, and are discharged to the positive electrode mixture layer 11B via the nonaqueous electrolyte. Occluded.

  Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. Specifically, the operations described in the following examples were performed to produce a cylindrical secondary battery as shown in FIGS. 1 and 2, and its performance was evaluated.

(Example 1-1)
<Preparation of positive electrode>
First, a coprecipitated hydroxide represented by LiOH and Co _0.98 Al _0.01 Mg _0.01 (OH) ₂ was mixed in a mortar so that Li: total transition metals = 1: 1 (molar ratio). Next, the mixture was heat-treated at 800 ° C. for 12 hours in an air atmosphere, pulverized, and lithium-cobalt composite oxide (composition formula: LiCo _0.98 Al _0.01 Mg _0.01 O ₂ , BET specific surface area: 0.44 m ² / g, average particle diameter: 6.2 μm) (hereinafter sometimes referred to as “lithium-cobalt composite oxide (A)”) and lithium-cobalt composite oxide (composition formula: LiCo _0.98 Al _0.01 Mg _0.01 O _2). , BET specific surface area: 0.20 m ² / g, average particle diameter: 16.7 μm) (hereinafter sometimes referred to as “lithium-cobalt composite oxide (B)”).
Thereafter, the obtained lithium-cobalt composite oxide (A) and (B) were mixed at a lithium-cobalt composite oxide (A): lithium-cobalt composite oxide (B) = 85: 15 (mass ratio). Thus, a positive electrode active material I was obtained. When the positive electrode active material I was analyzed by X-ray diffraction using CuKα, it was found to be an R-3 rhombohedral layered rock salt structure.

Next, the positive electrode active material I, nickel oxide having an average particle diameter of 1 μm, and manganese oxide having an average particle diameter of 1 μm are obtained as positive electrode active material I: nickel oxide: manganese oxide = 96: 2: 2 (mass ratio). After mixing, dry mixing was performed using a mechanofusion system manufactured by Hosokawa Micron Corporation, and the positive electrode active material I was coated with nickel oxide and manganese oxide.
Thereafter, it was baked in air at 950 ° C. for 10 hours to obtain a positive electrode active material II having a structure in which the surface of the positive electrode active material I was covered with nickel oxide and manganese oxide.
This positive electrode active material II was used as the positive electrode active material used in the production of the positive electrode of this example. The average particle diameter was not significantly different from that of the positive electrode active material I.

Next, the obtained positive electrode active material, ketjen black as a conductive agent, and polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Next, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent to form a positive electrode mixture slurry, which is applied to both sides of a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 15 μm and dried. The positive electrode was produced by compression molding with a roll press machine to form a positive electrode mixture layer.
Thereafter, an aluminum positive electrode lead was attached to the positive electrode current collector.
In addition, when the density per unit area (surface density) was investigated about the positive mix layer, it was 3.65 g / cm < ² >.

<Production of negative electrode>
Next, granular artificial graphite powder (BET specific surface area: 3.0 m ² / g) as a negative electrode material, vapor growth carbon fiber as a conductive agent, styrene butadiene rubber (SBR) and carboxymethyl cellulose as a binder Were mixed with ion-exchanged water to prepare a negative electrode mixture slurry.
Next, the negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 8 μm, dried, and compression-molded with a roll press to form a negative electrode mixture layer, thereby preparing a negative electrode.
Thereafter, a negative electrode lead made of nickel was attached to the negative electrode current collector.
In addition, when the density (area density) per unit area was investigated about the negative mix layer, it was 1.70 g / cm < ² >. The amount of the positive electrode material and the negative electrode material was designed so that the open circuit voltage at the time of full charge was 4.35V.

<Production of separator with heat-resistant insulating layer>
Next, dry anhydrous calcium chloride was dissolved in NMP to prepare a 6% calcium chloride solution. Next, an aramid resin (fibrous) was added to the obtained NMP solution of calcium chloride to prepare an NMP solution of an aramid resin. Next, alumina was further added to the obtained NMP solution of aramid resin so that aramid resin: alumina = 40: 60 (mass ratio) to prepare an aramid solution in which alumina was dispersed. Next, the aramid solution in which alumina was dispersed was applied to one side of a microporous polyethylene separator having a thickness of 16 μm by a doctor blade and dried with hot air at 80 ° C. Further, the aramid resin film was sufficiently washed with pure water to remove calcium chloride, and at the same time, micropores were formed in the film and dried.
Thereby, a 4 μm heat-resistant insulating layer was formed on one surface of the microporous polyethylene separator to produce a separator with a heat-resistant insulating layer.
The heat-resistant insulating layer has irregularly formed holes. As a result of measuring the cross section of the separator with the heat-resistant insulating layer by a scanning electron microscope (SEM), the average pore diameter is about 0.7 μm and the porosity is about 50%. there were.

<Preparation of non-aqueous electrolyte>
On the other hand, the non-aqueous electrolyte includes ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and 4-fluoroethylene carbonate, and ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate: 4-fluoroethylene carbonate = 23: 67: 6: 4 ( A solution in which LiPF ₆ was further dissolved as an electrolyte salt was used in a solvent mixed at a ratio of (mass ratio). LiPF ₆ was dissolved at a concentration of 1.5 mol / kg.

<Production of wound electrode body>
Next, the obtained positive electrode and negative electrode were laminated via the obtained separator with a heat-resistant insulating layer and wound many times in a spiral shape to produce a jelly roll type wound electrode body.
In addition, the electrode length of the positive electrode and the negative electrode was adjusted so that the element diameter might be 17.20 mm by using a 3.5φ winding core.
Further, the widths of the strip-shaped separator, the negative electrode, and the positive electrode were in a relationship of (separator width)> (negative electrode width)> (positive electrode width).

<Assembly of cylindrical secondary battery>
Next, the produced wound electrode body was sandwiched between a pair of insulating plates, the negative electrode lead was welded to the battery can, and the positive electrode lead was welded to the safety valve mechanism, and the wound electrode body was housed inside the battery can.
Thereafter, a non-aqueous electrolyte is injected into the battery can, and the battery lid is caulked to the battery can through a gasket, whereby the cylindrical secondary battery of this example having an outer diameter of 18 mm and a height of 65 mm is obtained. Obtained.
Table 1 shows a part of the specifications of the cylindrical secondary battery of each example.

(Example 1-2, Example 1-3, Comparative Example 1-1 to Comparative Example 1-3)
Except that the ratio of aramid and alumina in the heat-resistant insulating layer was changed as shown in Table 1, the same operation as in Example 1-1 was repeated to obtain a cylindrical secondary battery of each example.

(Comparative Example 1-4)
When the same operation as in Example 1-1 was repeated except that the ratio of aramid and alumina in the heat-resistant insulating layer was changed as shown in Table 1, a cylindrical secondary battery could not be produced.

(Comparative Example 1-5)
A cylindrical secondary battery of this example was obtained by repeating the same operation as in Example 1-1 except that the use charge upper limit voltage was set to 4.20V.

(Example 2-1)
Except that the heat-resistant insulating layers were formed on both the positive electrode side and the negative electrode side, the same operation as in Example 1-1 was repeated to obtain a cylindrical secondary battery of this example. At that time, the heat-resistant insulating layer was formed on one side of the microporous polyethylene separator with a thickness of 2 μm, and the total thickness of the double-sided layers was 4 μm.

(Comparative Example 2-1)
Except having formed the heat-resistant insulating layer in the negative electrode side, the same operation as Example 1-1 was repeated and the cylindrical secondary battery of this example was obtained.
Table 2 shows a part of the specifications of the cylindrical secondary battery of each example.

(Example 3-1 to Example 3-4)
The cylindrical secondary battery of each example was repeated except that the ratio of the surface density of the positive electrode mixture layer to the surface density of the negative electrode mixture layer was changed as shown in Table 3, and the same operation as in Example 1-1 was repeated. Got.
Table 3 shows a part of the specifications of the cylindrical secondary battery of each example.

[Performance evaluation]
<Initial charge / discharge>
About the produced cylindrical secondary battery of each example, constant current-constant voltage charge (CCCV charge) was performed at 25 degreeC with the electric current corresponded to 0.1 C with the use charge upper limit voltage shown in Tables 1-3. Subsequently, the battery was stored at 45 ° C. for 2 days. Subsequently, it was stored at 23 ° C. for 1 day. Further, discharging was performed at a current corresponding to 0.2 C until 3.0 V was reached. Thereafter, charging / discharging was repeated 5 times with a current corresponding to 0.5 C within a range of 3.0 V to the upper limit voltage for use shown in Tables 1-3.
And the discharge capacity of the 5th cycle was made into the rated discharge capacity. In Tables 1-3, the rated discharge capacity (rated capacity) per 1 g of the positive electrode active material is also shown.

<High temperature cycle test>
About the cylindrical secondary battery of each example which performed initial charge / discharge, constant current-constant voltage charge (CCCV charge) was performed at 25 degreeC with the use charge upper limit voltage shown in Tables 1-3. Next, 0.5 C discharge was performed to obtain an initial capacity.
Next, the obtained cylindrical secondary batteries were charged and discharged at 25 ° C. again, and the discharge capacity at the fifth cycle and the discharge capacity at the 200th cycle were examined. ) Was calculated. The obtained results are also shown in Tables 1-3.
At that time, charging is performed at a constant voltage-constant current up to the upper limit voltage for use at 0.7C, and then the charging current is attenuated to 50 mA at the upper limit voltage for use, and discharging is performed at a constant current of 0.5C. This was done until the voltage reached 3.0V.
The capacity maintenance rate at the 200th cycle was determined as the ratio of the discharge capacity at the 200th cycle to the discharge capacity at the 5th cycle (discharge capacity at the 200th cycle / discharge capacity at the 5th cycle) × 100 (%).

<Heating test>
About the cylindrical secondary battery of each example which performed initial charge / discharge, it charged to the use charge upper limit voltage shown in Tables 1-3 at a constant current of 0.5 C at 25 ° C., and then charged to 50 mA at a constant voltage. went. Subsequently, it was heated in an oven at a rate of 5 ° C./minute from 25 ° C. until reaching 135 ° C., and then left at 135 ° C. for 3 hours. At that time, the surface temperature of the battery was evaluated, and the battery burned was determined to be unsatisfactory (x), and the battery that did not burn was rated good (O). The number of specimens (n) was 3. The obtained results are also shown in Tables 1-3.

From Table 1, it can be seen that when the ratio of aramid to alumina is 40:60 to 10:90, a high capacity retention rate is exhibited in the high-temperature cycle, and the heating test results are all good. On the other hand, when the ratio of aramid to alumina is 100: 0 to 50:50, it can be seen that although the heating test is good, the high-temperature cycle characteristics are remarkably lowered.
It can also be seen that when a separator with a heat-resistant insulating layer having an aramid / alumina ratio of 8:92 is used, the result of the heating test is deteriorated. Furthermore, a separator could not be produced only with alumina, and the battery could not be assembled.
This is considered as follows. In the range of aramid: alumina up to 100: 0 to 50:50, since the aramid, which is a heat-resistant resin, is bonded to the base polyethylene, the heat shrinkage of the polyethylene separator during heating is suppressed, and high heating Can withstand testing. However, since it is exposed to a high charging voltage, it deteriorates by oxidation and is considered to be greatly deteriorated during a high-temperature cycle.
Therefore, by increasing the proportion of alumina, which is an oxidation-resistant ceramic particle, it was possible to prevent oxidative deterioration in a high charging range and to contain a heat-resistant resin, thereby preventing thermal shrinkage and obtaining a good heating test. Presumed to be.
In addition, Comparative Example 1-5 showed an experimental result using lithium cobalt oxide coated with the positive electrode active material Ni—Mn and setting the open circuit voltage at the time of full charge to 4.20V. The areal density ratio at this time was 2.25. Although not shown in the table, a high capacity retention ratio in a high-temperature cycle and a good heating test result are obtained at any ratio of aramid and alumina. Further, although not shown in the table, unlike the example shown in Table 3, even when the area ratio is 2.15 or more, high temperature cycle characteristics are shown.
However, it can be seen that since the charging potential of the positive electrode is low, the utilization factor of the positive electrode is low, and therefore only a low battery capacity can be obtained.

  From Table 2, in the example in which the heat-resistant insulating layer is disposed on the negative electrode side, good results were obtained in the heating test, but since the high-temperature cycle characteristics were degraded, the heat-resistant insulating layer was disposed on the positive electrode side. It turns out that it is necessary to be installed.

From Table 3, it can be seen that high cycle characteristics and a good heating test are obtained when the surface density ratio is in the range of 1.90 to 2.10.
At that time, when the areal density ratio is small, the negative electrode mass is relatively larger than the positive electrode mass, so that the battery cell capacity tends to be small. On the other hand, it can be seen that when the surface density ratio is 2.15 or more, both the cycle characteristics and the heating test are lowered. This is because the total lithium charge capacity extracted from the positive electrode is too much relative to the total lithium discharge capacity received by the negative electrode, so that when lithium is charged, the metal lithium that shows high reactivity with the electrolyte is present. This is thought to be because it was deposited on the negative electrode and deteriorated.

As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.
For example, in the above embodiment, the case where a battery element in which a negative electrode and a positive electrode are stacked and wound is described, but a flat battery element having a structure in which a pair of positive and negative electrodes are folded or stacked, or The present invention can also be applied to a case where a stacked battery element in which a plurality of positive electrodes and negative electrodes are stacked is provided.
In the above embodiment, the case where a battery can or a film-shaped exterior member is used has been described. However, the present invention is similarly applied to a battery having another shape such as a so-called square shape, coin shape, or button shape. be able to.

  Further, in the above embodiments and examples, a so-called lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium has been described. However, the present invention relates to lithium metal as the negative electrode active material. The capacity of the negative electrode used is a so-called lithium metal secondary battery represented by a capacity component due to precipitation and dissolution of lithium, or the charge capacity of the negative electrode material capable of inserting and extracting lithium is higher than the charge capacity of the positive electrode. The same applies to a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof, by reducing the capacity. be able to.

  Furthermore, as described above, the present invention relates to a battery using lithium as an electrode reactant, but the technical idea of the present invention is that other alkali metals such as sodium (Na) or potassium (K), magnesium The present invention can also be applied to the case of using an alkaline earth metal such as (Mg) or calcium (Ca), or another light metal such as aluminum.

  DESCRIPTION OF SYMBOLS 1A ... Battery can, 1B ... Battery cover, 2A, 2B ... Insulating plate, 3 ... Safety valve mechanism, 3A ... Disk board, 4 ... Heat sensitive resistance element, 5 ... Gasket, 6 ... Center pin, 7 ... Positive electrode lead, 8 ... Negative electrode lead, 10 ... Battery element, 10A ... Winding electrode body, 11 ... Positive electrode, 11A ... Positive electrode current collector, 11B ... Positive electrode mixture layer, 12 ... Negative electrode, 12A ... Negative electrode current collector, 12B ... Negative electrode mixture layer , 14 ... Separator with heat-resistant insulating layer, 14A ... Polyolefin layer, 14B heat-resistant insulating layer

Claims (4)

A positive electrode formed by forming a positive electrode mixture layer containing a positive electrode active material on a positive electrode current collector, a negative electrode formed by forming a negative electrode mixture layer on a negative electrode current collector, a separator with a heat-resistant insulating layer, a non-aqueous electrolyte, A non-aqueous electrolyte secondary battery comprising:
The open circuit voltage in a fully charged state per pair of positive and negative electrodes is 4.25 to 4.35 V,
The separator with a heat-resistant insulating layer comprises a polyolefin layer, and a heat-resistant insulating layer formed on one or both surfaces of the polyolefin layer and containing a heat-resistant resin and oxidation-resistant ceramic particles.
The heat-resistant insulating layer contains the oxidation-resistant ceramic particles in a proportion of 80 to 90%, the heat-resistant resin contains at least an aromatic polyamide, and the heat-resistant insulating layer comprises the positive electrode and the polyolefin layer. non-aqueous electrolyte secondary battery which is arranged between the. The oxidation-resistant ceramic particles contain at least alumina.
The nonaqueous electrolyte secondary battery according to claim 1. The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a ratio of a surface density of the positive electrode mixture layer to a surface density of the negative electrode mixture layer is 1.90 to 2.10. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a positive electrode active material in which at least part or all of the surface of lithium cobalt oxide is coated with an oxide containing nickel and / or manganese.

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