JP4834284B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

【００６１】
表１から明らかなように、ＣＨＢ量が０．０９〜０．１６（ｍｇ／ｍＡｈ）で、かつセパレータ透気度が２００（sec./100mL）以上、８００（sec./100mL）未満である実施例１〜１４の二次電池は、過充電時の最高温度が１３０℃より低く、かつ低温放電特性に優れていることが理解できる。過充電時の急激な温度上昇が抑えられたのは、ＣＨＢのセパレータへの析出反応が生じたためであると推測される。この際、ＣＨＢ量が０．１（ｍｇ／ｍＡｈ）以上で、かつセパレータの透気度が４５０（sec./100mL）未満であると、マイクロショートの発生率が高くなるため、温度上昇抑制の効果がより高くなる。
【００６２】
これに対し、ＣＨＢ量が０．０９（ｍｇ／ｍＡｈ）未満の比較例１〜３の二次電池は、過充電時の最高温度が１５０℃を超え、セパレータの透気度が８００（sec./100mL）未満の比較例１，２に至ってはセパレータが溶融により破膜した。セパレータの透気度が８００（sec./100mL）である比較例４〜８の二次電池では、ＣＨＢ量が０．０９〜０．１６（ｍｇ／ｍＡｈ）であっても、過充電時の最高温度が１５０℃を超えるか、あるいは低温放電特性が低くなった。このことから、セパレータの透気度が８００（sec./100mL）以上であると、ＣＨＢ量が０．０９〜０．１６（ｍｇ／ｍＡｈ）であってもＣＨＢのセパレータへの析出及びＣＨＢ析出によるマイクロショートが起きないために過充電時に急激な温度上昇が生じることと、過充電時の温度上昇を抑えるためにＣＨＢ添加量を多くすると、ＣＨＢ量が０．０９〜０．１６（ｍｇ／ｍＡｈ）であっても低温放電特性が低下することが理解できる。
【００６３】
一方、ＣＨＢ量が０．１６（ｍｇ／ｍＡｈ）より多い比較例９〜１０の二次電池は、過充電時の最高温度が１３０℃より低いが、低温放電特性が劣っていた。
【００６４】
なお、本発明は上記実施形態そのままに限定されるものではなく、実施段階ではその要旨を逸脱しない範囲で構成要素を変形して具体化できる。また、上記実施形態に開示されている複数の構成要素の適宜な組み合わせにより、種々の発明を形成できる。例えば、実施形態に示される全構成要素から幾つかの構成要素を削除してもよい。さらに、異なる実施形態にわたる構成要素を適宜組み合わせてもよい。
【００６５】
【発明の効果】
以上詳述したように本発明によれば、低温放電特性に優れ、かつ過充電時の急激な温度上昇が抑制された非水電解質二次電池を提供することができる。
【図面の簡単な説明】
【図１】 本発明に係わる非水電解質二次電池の一実施形態である薄型非水電解質二次電池を示す断面図。
【図２】 図２は図１のＡ部を示す拡大断面図。
【符号の説明】
１…容器本体、２…電極群、３…正極、４…負極、５…セパレータ、６…蓋板、７…外部保護層、８…内部保護層、９…金属層、１０…正極端子、１１…負極端子。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery.
[0002]
[Prior art]
In recent years, with the diversification, miniaturization, and weight reduction of various portable electrical and electronic devices, there is a demand for diversification, miniaturization, and weight reduction for secondary batteries used as driving sources. It is getting stronger.
[0003]
As such a secondary battery, research and development of a non-aqueous solvent secondary battery using an organic electrolyte has been actively conducted recently, and some of them have already been put into practical use. This non-aqueous solvent secondary battery generally has an advantage that it has a high energy density, less self-discharge during storage and storage, and can take out current even in a wide range of environmental temperature of -20 to 60 ° C. I have.
[0004]
As the positive electrode active material of this non-aqueous solvent secondary battery, a material that allows Li ⁺ to reversibly enter and exit directly in its crystal structure, such as V ₂ O ₅ and Mn oxide, or LiMn ₂ O ₄ In addition, a material having a spinel crystal structure in which a Li source involved in charge / discharge is coordinated as Li ⁺ is used. Non-aqueous electrolytes include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone (γ-BL), 1,2-diethoxyethane (DEE), 1,2 An electrolyte (LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiPF ₆ and LiN (CF ₃ SO ₂ ) in one or more non-aqueous solvents selected from the group consisting of dimethoxyethane (DME) and diethyl carbonate (DEC) _In which at least one kind selected from the group consisting of ₂ ) is dissolved is used.
[0005]
Among such non-aqueous solvent secondary batteries, a secondary battery using LiCoO ₂ as a positive electrode active material has a high electromotive force of about 4 V and a theoretical energy density of about 1 kWh / kg per positive electrode active material. . This secondary battery has already been put into practical use as a power source for mobile devices such as mobile phones that are becoming smaller and lighter.
[0006]
However, lithium-containing cobalt oxides such as LiCoO ₂ are inferior in thermal stability, and there is a risk that the battery will abnormally generate heat when overcharged, resulting in ignition.
[0007]
JP 2002-203594 A (Patent Document 1) and the like have proposed the addition of cyclohexylbenzene to a non-aqueous electrolyte in order to enhance safety during overcharge. In Patent Document 1, a non-aqueous electrolyte containing 0.001 to 5% by weight of a disulfide derivative and 0.1 to 5% by weight of cyclohexylbenzene is used for a lithium secondary battery, whereby cyclohexyl during overcharging is used. It is described that a decomposition coating is formed by a decomposition reaction of benzene to improve safety during overcharge.
[0008]
However, since the decomposition reaction of cyclohexylbenzene is an exothermic reaction, according to the lithium secondary battery described in Patent Document 1, the battery temperature rapidly rises due to the heat generation of cyclohexylbenzene and the Joule heat due to overcharge current. However, there is a problem that the film breaks due to melting, the positive electrode and the negative electrode are short-circuited, and thermal runaway occurs.
[0009]
[Patent Document 1]
JP 2002-203594 A (claims, paragraphs [0016] to [0018])
[0010]
[Problems to be solved by the invention]
An object of this invention is to provide the nonaqueous electrolyte secondary battery which can suppress the rapid temperature rise at the time of overcharge, without impairing a low-temperature discharge characteristic.
[0011]
[Means for Solving the Problems]
A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode,
A negative electrode,
A separator disposed between the positive electrode and the negative electrode and having a thickness in the range of 10 to 22 μm and an air permeability in the range of 200 (sec./100 mL) to less than 800 (sec./100 mL) When,
0.09 mg to 0.16 mg of cyclohexylbenzene per 1 mAh of battery capacity, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2 A non-aqueous solvent comprising at least one solvent selected from the group consisting of methyltetrahydrofuran, 1,3-dioxolane, 1,3-dimethoxypropane and vinylene carbonate {amine aromatic, sulfide aromatic, R- Represented by SLi (R is a substituent containing an aromatic group such as an allyl group), excluding those containing any of aromatic, phosphite aromatic and quinone aromatic}, and dissolved in the non-aqueous solvent. A non-aqueous electrolyte consisting of It is characterized in that Bei.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a non-aqueous electrolyte secondary battery according to the present invention will be described.
[0013]
The nonaqueous electrolyte secondary battery is disposed between a container, a positive electrode housed in the container, a negative electrode housed in the container, the positive electrode and the negative electrode, and has a thickness of 10 to 22 μm. And a separator whose air permeability is in the range of 200 (sec./100 mL) or more and less than 800 (sec./100 mL) and 0.09 mg to 0.16 mg per 1 mAh of battery capacity that is housed in the container. And a non-aqueous electrolyte containing cyclohexylbenzene.
[0014]
Hereinafter, the positive electrode, the negative electrode, the separator, the nonaqueous electrolyte, and the container will be described.
[0015]
1) Positive electrode The positive electrode contains a positive electrode active material. Examples of the positive electrode active material include lithium-containing cobalt oxide (for example, LiCoO ₂ ).
[0016]
In this positive electrode, for example, a positive electrode active material, a conductive agent and a binder are suspended in a suitable solvent, and the resulting mixture slurry is applied to one or both sides of a current collector substrate, dried, and thinned. It is produced by cutting the shape into a desired size. Alternatively, a positive electrode active material formed into a pellet shape together with a conductive agent and a binder is used as a positive electrode, or a kneaded mixture of a positive electrode active material, a conductive agent and a binder is formed into a sheet, which is attached to a current collector. Thus, a positive electrode may be obtained.
[0017]
Examples of the conductive agent include carbon materials such as acetylene black, carbon black, natural graphite, and artificial graphite, metal powder, and conductive oxide.
[0018]
Examples of the binder include polyvinylidene fluoride (PVdF), vinylidene fluoride-6-propylene fluoride copolymer, vinylidene fluoride-tetrafluoroethylene-6-fluoropropylene copolymer, and vinylidene fluoride-pentafluoro. Propylene copolymer, tetrafluoroethylene-vinylidene fluoride copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether (PFA) -vinylidene fluoride terpolymer, tetrafluoroethylene-hexafluoropropylene (FEP) -fluorination Vinylidene terpolymer, tetrafluoroethylene-ethylene-vinylidene fluoride terpolymer, chlorotrifluoroethylene-vinylidene fluoride copolymer, chlorotrifluoroethylene-ethylene-vinylidene fluoride terpolymer, Vinyl fluoride - vinylidene fluoride copolymer, an ethylene - propylene - diene copolymer (EPDM), styrene - can be used butadiene rubber (SBR) and the like.
[0019]
As the current collector, for example, aluminum foil, stainless steel foil, titanium foil or the like can be used, but aluminum foil is most preferable in consideration of tensile strength, electrochemical stability, flexibility during winding, and the like. The thickness of the foil at this time is preferably 8 μm or more and 30 μm or less.
[0020]
The positive electrode active material preferably has an average particle diameter D50 in the range of 2 to 20 μm in consideration of adhesion to the substrate and electrochemical characteristics during electrode production. The specific surface area of the positive electrode active material is preferably 0.5 to ² m ² / g from the viewpoint of improving the active material packing density and charge / discharge efficiency of the positive electrode and suppressing the decomposition reaction of the nonaqueous electrolyte. .
[0021]
2) Negative electrode A negative electrode contains a negative electrode active material. Examples of the negative electrode active material include compounds that occlude and release lithium ions.
[0022]
Examples of the compound that occludes and releases lithium ions include, for example, a conductive polymer such as polyacetal, polyacetylene, and polypyrrole that can be doped with lithium, and an organic material sintered body that can be doped with lithium ions. Examples thereof include materials and lithium metal oxides.
[0023]
Various types of carbon materials can be used. Examples thereof include graphite-based carbon, carbon in which a graphite crystal part and an amorphous part are mixed, and a carbon material having a disordered layer structure with no regularity in a crystal layer stack.
[0024]
The negative electrode containing the carbon material is specifically produced by the following method. The carbon material and the binder are suspended in a suitable solvent, the mixture slurry is applied to one or both sides of a current collector, and dried to form a thin plate, which is cut into a desired size. To obtain a negative electrode. Or you may use the pellet which shape | molded the carbon material with the binder as a negative electrode, or knead | mix a carbon material and a binder, and you may obtain a negative electrode by sticking it to a collector.
[0025]
Examples of the binder include the same ones as described for the positive electrode.
[0026]
As the current collector, for example, copper foil, nickel foil or the like can be used, but copper foil is most preferable. The current collector made of foil can not only improve the tensile strength and electrochemical stability, but also can increase the flexibility during winding. The thickness of the current collector is preferably 8 μm or more and 20 μm or less.
[0027]
3) Separator This separator is formed from a porous sheet having a thickness in the range of 10 to 22 μm and an air permeability in the range of 200 (sec./100 mL) to less than 800 (sec./100 mL). Is done.
[0028]
For example, a porous film or a non-woven fabric can be used as the porous sheet. The porous sheet is preferably formed of at least one material selected from, for example, polyolefin and cellulose. Examples of the polyolefin include polyethylene and polypropylene. Among these, a porous film made of polyethylene, polypropylene, or both is preferable because it can improve the safety of the secondary battery.
[0029]
The reason why the air permeability of the separator is defined in the above range is for the reason described below. If the air permeability is less than 200 (sec./100 mL), the separator is likely to break due to melting during overcharging, and a short circuit is likely to occur, so the firing rate during overcharging increases. On the other hand, when the air permeability is set to 800 (sec./100 mL) or more, the lithium ion permeability of the separator is lowered, so that the low-temperature discharge characteristics are lowered. Moreover, since the CHB deposition reaction on the separator does not occur during overcharge, there is a risk that the battery will reach an abnormally high temperature during overcharge, resulting in explosion or fire. A more preferable range of the air permeability is 250 to 750 (sec./100 mL). However, in order to prevent the separator from being cut at the time of producing the electrode group and to obtain sufficient charge / discharge cycle characteristics, the air permeability is 300 to More preferably, it is within the range of 750 (sec./100 mL).
[0030]
The air permeability of the separator means the time (seconds) required for 100 cm ³ of air to pass through the separator, and can be measured by a method defined in JIS (Japanese Industrial Standard) P8117.
[0031]
The reason why the thickness of the separator is defined within the above range is for the reason described below. When the thickness is less than 10 μm, the film is easily broken when the separator is melted during overcharge. On the other hand, when the thickness exceeds 22 μm, the lithium ion permeability of the separator is lowered, so that the low-temperature discharge characteristics are lowered. A more preferable range of the thickness is 14 to 20 μm.
[0032]
4) Nonaqueous electrolyte This nonaqueous electrolyte includes a nonaqueous solvent containing cyclohexylbenzene (CHB) and an electrolyte dissolved in the nonaqueous solvent. The CHB amount is in the range of 0.09 mg to 0.16 mg per 1 mAh of battery capacity.
[0033]
A non-aqueous electrolyte having a liquid or gel form can be used. The liquid nonaqueous electrolyte is prepared, for example, by dissolving a lithium salt in a nonaqueous solvent. On the other hand, the gel-like nonaqueous electrolyte includes a composite of a liquid nonaqueous electrolyte and a polymer material. Examples of the polymer material include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), polyvinyl chloride (PVC), polyacrylate (PMMA), and polyvinylidene fluoride hexafluoropropylene (PVdF- At least one selected from HFP) can be used.
[0034]
If the amount of CHB per 1 mAh of battery capacity is less than 0.09 mg, the incidence of micro shorts caused by CHB depositing on the separator during overcharge decreases, leading to abnormally high temperatures during overcharge, which may cause rupture or ignition There is sex. On the other hand, when the CHB content per 1 mAh of battery capacity exceeds 0.16 mg, the ionic conductivity of the nonaqueous electrolyte is lowered, so that the low temperature discharge characteristics are lowered. A more preferable range of the CHB content is 0.09 to 0.13 mg per 1 mAh of battery capacity.
[0035]
It is desirable to satisfy the following formula (1) when the amount of CHB is B (mg) and the battery capacity is A (mAh).
[0036]
A / 20 <B <A / 5 (1)
If the amount of CHB (B) is less than (A / 20) mg, there is a risk of rupture or ignition during overcharge. On the other hand, when the amount of CHB (B) exceeds (A / 5) mg, not only low temperature discharge characteristics but also discharge characteristics at room temperature and charge / discharge cycle life may be reduced.
[0037]
The non-aqueous solvent can contain a solvent other than CHB (hereinafter referred to as the second solvent). Examples of the second solvent include propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), Diethoxyethane (DEE), γ-butyrolactone (γ-BL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane, 1,3-dimethoxypropane, vinylene carbonate (VC), etc. Can be mentioned. As the second solvent, one or two or more mixed solvents selected from the types described above can be used.
[0038]
Examples of the lithium salt (electrolyte) include lithium perchlorate (LiClO ₄ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and lithium hexafluorophosphate (LiPF _6). ), Lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ), and the like. As the lithium salt, one type or two or more types selected from the types described above can be used. Among these, lithium borofluoride (LiBF ₄ ) is preferable because it can suppress gas generation during the initial charge.
[0039]
The amount of the lithium salt dissolved in the non-aqueous solvent is preferably 1 to 3 mol / L. More preferably, it is the range of 2-2.5 mol / L.
[0040]
5) The shape of the container can be, for example, a bottomed cylindrical shape, a bottomed rectangular tube shape, a bag shape, a cup shape, or the like.
[0041]
The container can be formed of, for example, a resin, a sheet including a resin layer, a metal plate, a metal film, or the like.
[0042]
Examples of the resin include polyolefins such as polyethylene and polypropylene.
[0043]
The resin layer included in the sheet can be formed from, for example, polyethylene, polypropylene, or the like. As the sheet, it is desirable to use a sheet in which a metal layer and protective layers disposed on both sides of the metal layer are integrated. The metal layer serves to block moisture. Examples of the metal layer include aluminum, stainless steel, iron, copper, and nickel. Among these, aluminum that is lightweight and has a high function of blocking moisture is preferable. The metal layer may be formed from one type of metal, but may be formed from a combination of two or more types of metal layers. Of the two protective layers, the protective layer in contact with the outside serves to prevent damage to the metal layer. This external protective layer is formed of one type of resin layer or two or more types of resin layers. On the other hand, the internal protective layer plays a role of preventing the metal layer from being corroded by the non-aqueous electrolyte. This internal protective layer is formed of one type of resin layer or two or more types of resin layers. In addition, a thermoplastic resin can be disposed on the surface of the internal protective layer.
[0044]
The metal plate and the metal film can be formed of, for example, iron, stainless steel, or aluminum.
[0045]
The nonaqueous electrolyte secondary battery according to the present invention can have various forms such as a cylindrical shape, a rectangular shape, and a thin shape. Of these, a thin lithium ion secondary battery will be described in detail with reference to FIGS.
[0046]
As shown in FIG. 1, an electrode group 2 is accommodated in the container 1. The electrode group 2 has a structure in which a laminate composed of a positive electrode, a separator, and a negative electrode is wound into a flat shape. As shown in FIG. 2, the laminate includes a separator 3, a positive electrode layer 4, a positive electrode current collector 5, a positive electrode 6 including a positive electrode layer 4, a separator 3, a negative electrode layer 7, and a negative electrode collector. A negative electrode 9 including a current collector 8 and a negative electrode layer 7, a separator 3, a positive electrode layer 4, a positive electrode current collector 5, a positive electrode 6 including a positive electrode layer 4, a separator 3, a negative electrode layer 7, and a negative electrode current collector 8 are provided. The negative electrode 9 is formed by laminating in this order. In the electrode group 2, the negative electrode current collector 8 is located in the outermost layer. One end of the strip-like positive electrode lead 10 is connected to the positive electrode current collector 5 of the electrode group 2 and the other end is extended from the container 1. On the other hand, one end of the strip-shaped negative electrode lead 11 is connected to the negative electrode current collector 8 of the electrode group 2 and the other end is extended from the container 1.
[0047]
In FIGS. 1 and 2, the electrode group in which the positive electrode and the negative electrode are wound in a flat shape with a separator interposed therebetween is used. However, the electrode group obtained by folding the positive electrode and the negative electrode through the separator. Alternatively, an electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween may be used.
[0048]
As described above, the nonaqueous electrolyte secondary battery according to the present invention has a thickness in the range of 10 to 22 μm and an air permeability of 200 (sec./100 mL) or more and less than 800 (sec./100 mL). And a non-aqueous electrolyte containing 0.09 mg to 0.16 mg of cyclohexylbenzene (CHB) per 1 mAh of battery capacity, so that the decomposition product generated by the decomposition reaction of CHB during overcharge Things are likely to deposit on the separator, and this deposit can cause a micro short (short circuit with a slight voltage drop) between the positive electrode and the negative electrode. Overcharge current is consumed due to the deposition of CHB on the separator and the occurrence of micro-shorts, and the generation of Joule heat due to overcharge current can be suppressed by the amount consumed, thereby suppressing a rapid rise in battery temperature. It is possible to prevent film breakage due to melting of the separator, that is, internal short circuit. As a result, since the thermal runaway reaction of the positive electrode can be avoided, rupture and ignition during overcharge can be prevented.
[0049]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0050]
Example 1
<Preparation of positive electrode>
After adding 5 parts by weight of acetylene black to 100 parts by weight of LiCoO ₂ powder and mixing them with a ball mill for 1 hour, an N-methyl-2-pyrrolidone solution in which 4% by weight of polyvinylidene fluoride was dissolved was added and further mixed. Thus, a mixture slurry was prepared. The mixture slurry was applied to an aluminum foil having a thickness of 15 μm, dried, and then heated and pressed to obtain a positive electrode.
[0051]
<Production of negative electrode>
The mesophase pitch-based carbon fiber was graphitized at 3000 ° C. in an argon gas atmosphere, and further heat treated in a chlorine gas atmosphere at 2400 ° C. to synthesize graphitized carbon powder. Subsequently, a mixture slurry was prepared by mixing 100 parts by weight of the graphitized carbon powder, 1 part by weight of cellulose fiber powder, and an N-methyl-2-pyrrolidone solution in which 5% by weight of polyvinylidene fluoride was dissolved. Was prepared. This mixture slurry was applied to a copper foil having a thickness of 12 μm, dried, and then heated and pressed to obtain a negative electrode.
[0052]
<Separator>
A polypropylene microporous film having a thickness of 20 μm and an air permeability of 250 (sec./100 mL) was prepared as a separator.
[0053]
<Preparation of non-aqueous electrolyte>
A non-aqueous solvent was prepared by mixing ethylene carbonate (EC) and methyl ethyl carbonate (MEC) so that the volume ratio (EC: MEC) was 1: 1. Lithium hexafluorophosphate (LiPF ₆₎ was added to the obtained non-aqueous solvent. ) Was dissolved so as to have a concentration of 1 mol / L to prepare a non-aqueous electrolyte.
[0054]
<Battery assembly>
The positive electrode, separator, and the like, in which an aluminum ribbon having a thickness of 100 μm and a length of 70 mm is ultrasonically welded to a predetermined position in advance as a current collecting tab of the positive electrode, and a polyimide protective tape for preventing a short circuit is attached to the welding site; The negative electrodes 100 μm thick and 70 mm long copper ribbons were ultrasonically welded to predetermined positions in advance, and the negative electrodes on which polyimide protective tapes for preventing short circuits were attached to the welded portions were arranged in this order. After being laminated, the substrate was wound into a flat shape and pressed for 30 seconds to produce an electrode group.
[0055]
A laminate film having a thickness of 100 μm, in which both surfaces of an aluminum foil are covered with polyethylene, is formed into a rectangular cup shape by a press, and an electrode group, a non-aqueous electrolyte, and the addition amount shown in Table 1 below are placed in the obtained container. A thin non-aqueous electrolyte secondary battery containing cyclohexylbenzene (CHB) and having the theoretical capacity of 1000 mAh (battery capacity A of 1000 mAh) having the structure shown in FIGS. 1 and 2 was assembled. The liquid injection process to the sealing process were performed in a glove box controlled to a dew point of −80 ° C. or lower in an Ar atmosphere.
[0056]
(Examples 2-14 and Comparative Examples 1-10)
A thin nonaqueous electrolyte secondary battery having the same configuration as described in Example 1 except that the theoretical capacity of the battery, the CHB addition amount, and the air permeability of the separator are set as shown in Table 1 below. Assembled.
[0057]
The obtained secondary battery was subjected to an overcharge test and a low-temperature discharge characteristic evaluation described below, and the results are shown in Table 1 below.
[0058]
<Overcharge test>
Constant current / constant voltage charging was performed at 1 CmA, 6 V, the maximum temperature at that time was measured, and the presence or absence of a short circuit was measured from changes in voltage and current. The results are shown in Table 1 below. In Table 1, “separator film breakage” indicates that the positive electrode and the negative electrode were in direct contact with each other due to melting of the separator, and the voltage dropped to 0V. In addition, when a minute voltage drop was observed during the overcharge test, it was determined that a micro short circuit occurred, and when no voltage drop was observed, it was determined that there was no short circuit.
[0059]
<Low-temperature discharge characteristics>
After a constant current / constant voltage charge of 4.2 V at a current of 1 C for 3 hours, the battery was left at -20 ° C. for 1 hour, and then at a low temperature environment of −20 ° C., a discharge rate of 0.5 C and a discharge end voltage of The discharge capacity when discharged under the condition of 0 V was measured. The obtained low-temperature discharge capacity is expressed as 100% of the discharge capacity when discharged under the same conditions at room temperature, and the result is shown in Table 1 below as the −20 ° C. discharge capacity retention rate.
[0060]
[Table 1]

[0061]
As apparent from Table 1, the CHB amount is 0.09 to 0.16 (mg / mAh), and the separator air permeability is 200 (sec./100 mL) or more and less than 800 (sec./100 mL). It can be understood that the secondary batteries of Examples 1 to 14 have a maximum temperature during overcharge lower than 130 ° C. and excellent low temperature discharge characteristics. It is presumed that the rapid temperature rise during overcharging was suppressed because of the precipitation reaction of CHB on the separator. At this time, if the CHB amount is 0.1 (mg / mAh) or more and the air permeability of the separator is less than 450 (sec./100 mL), the occurrence rate of micro-shorts is increased, and thus the temperature rise is suppressed. The effect is higher.
[0062]
In contrast, in the secondary batteries of Comparative Examples 1 to 3 having a CHB amount of less than 0.09 (mg / mAh), the maximum temperature during overcharge exceeds 150 ° C., and the air permeability of the separator is 800 (sec. In Comparative Examples 1 and 2 less than / 100 mL), the separator was broken by melting. In the secondary batteries of Comparative Examples 4 to 8 where the air permeability of the separator is 800 (sec./100 mL), even when the CHB amount is 0.09 to 0.16 (mg / mAh), The maximum temperature exceeded 150 ° C. or the low temperature discharge characteristics were lowered. From this, when the air permeability of the separator is 800 (sec./100 mL) or more, even when the CHB amount is 0.09 to 0.16 (mg / mAh), CHB is deposited on the separator and CHB is deposited. In order to prevent a rapid short-circuit during overcharge due to the occurrence of a micro-short due to, and to increase the amount of CHB added to suppress the temperature increase during overcharge, the CHB amount is 0.09 to 0.16 (mg / It can be understood that the low-temperature discharge characteristics deteriorate even with mAh).
[0063]
On the other hand, the secondary batteries of Comparative Examples 9 to 10 having a CHB amount greater than 0.16 (mg / mAh) had a low temperature discharge characteristic although the maximum temperature during overcharging was lower than 130 ° C.
[0064]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
[0065]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that is excellent in low-temperature discharge characteristics and in which a rapid temperature increase during overcharging is suppressed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a thin nonaqueous electrolyte secondary battery which is an embodiment of a nonaqueous electrolyte secondary battery according to the present invention.
FIG. 2 is an enlarged cross-sectional view showing a portion A of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Container main body, 2 ... Electrode group, 3 ... Positive electrode, 4 ... Negative electrode, 5 ... Separator, 6 ... Cover plate, 7 ... External protective layer, 8 ... Internal protective layer, 9 ... Metal layer, 10 ... Positive electrode terminal, 11 ... negative terminal.

Claims (1)

A positive electrode;
A negative electrode,
A separator disposed between the positive electrode and the negative electrode and having a thickness in the range of 10 to 22 μm and an air permeability in the range of 200 (sec./100 mL) to less than 800 (sec./100 mL) When,
0.09 mg to 0.16 mg of cyclohexylbenzene per 1 mAh of battery capacity, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2 A non-aqueous solvent comprising at least one solvent selected from the group consisting of methyltetrahydrofuran, 1,3-dioxolane, 1,3-dimethoxypropane and vinylene carbonate {amine aromatic, sulfide aromatic, R- Represented by SLi (R is a substituent containing an aromatic group such as an allyl group), excluding those containing any of aromatic, phosphite aromatic and quinone aromatic}, and dissolved in the non-aqueous solvent. A non-aqueous electrolyte consisting of Non-aqueous electrolyte secondary battery characterized by Bei.

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