JP4654700B2 - Lithium ion secondary battery - Google Patents
Lithium ion secondary battery Download PDFInfo
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- JP4654700B2 JP4654700B2 JP2005022427A JP2005022427A JP4654700B2 JP 4654700 B2 JP4654700 B2 JP 4654700B2 JP 2005022427 A JP2005022427 A JP 2005022427A JP 2005022427 A JP2005022427 A JP 2005022427A JP 4654700 B2 JP4654700 B2 JP 4654700B2
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims description 16
- 229910001416 lithium ion Inorganic materials 0.000 title claims description 16
- 239000000203 mixture Substances 0.000 claims description 45
- 239000012212 insulator Substances 0.000 claims description 30
- 238000004804 winding Methods 0.000 claims description 9
- 230000002093 peripheral effect Effects 0.000 claims description 6
- 239000000945 filler Substances 0.000 claims description 4
- 229910052809 inorganic oxide Inorganic materials 0.000 claims description 3
- 239000010408 film Substances 0.000 description 13
- 239000011347 resin Substances 0.000 description 10
- 229920005989 resin Polymers 0.000 description 10
- 239000011230 binding agent Substances 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- 239000012528 membrane Substances 0.000 description 8
- 239000004743 Polypropylene Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 239000002033 PVDF binder Substances 0.000 description 6
- 238000007600 charging Methods 0.000 description 6
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 4
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 4
- 239000011162 core material Substances 0.000 description 4
- 239000002003 electrode paste Substances 0.000 description 4
- 150000003949 imides Chemical class 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 238000013021 overheating Methods 0.000 description 4
- -1 polyethylene Polymers 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 3
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 3
- 230000005856 abnormality Effects 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 239000011888 foil Substances 0.000 description 3
- 238000007689 inspection Methods 0.000 description 3
- 238000009413 insulation Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 229910052744 lithium Inorganic materials 0.000 description 3
- 239000000155 melt Substances 0.000 description 3
- 229920003048 styrene butadiene rubber Polymers 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 2
- 239000002174 Styrene-butadiene Substances 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 2
- 229920000800 acrylic rubber Polymers 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 239000011324 bead Substances 0.000 description 2
- 239000012461 cellulose resin Substances 0.000 description 2
- 239000006258 conductive agent Substances 0.000 description 2
- 238000010277 constant-current charging Methods 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 238000001035 drying Methods 0.000 description 2
- 239000008151 electrolyte solution Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 229920000058 polyacrylate Polymers 0.000 description 2
- 229920000573 polyethylene Polymers 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000002562 thickening agent Substances 0.000 description 2
- 229910052723 transition metal Inorganic materials 0.000 description 2
- 150000003624 transition metals Chemical class 0.000 description 2
- 229910015118 LiMO Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- 239000004952 Polyamide Substances 0.000 description 1
- 239000004962 Polyamide-imide Substances 0.000 description 1
- 239000004642 Polyimide Substances 0.000 description 1
- 229910001069 Ti alloy Inorganic materials 0.000 description 1
- 239000006230 acetylene black Substances 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N acrylic acid group Chemical group C(C=C)(=O)O NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 238000009529 body temperature measurement Methods 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 239000001768 carboxy methyl cellulose Substances 0.000 description 1
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000010280 constant potential charging Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 239000007770 graphite material Substances 0.000 description 1
- 230000020169 heat generation Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 1
- 229910001947 lithium oxide Inorganic materials 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 229920002312 polyamide-imide Polymers 0.000 description 1
- 229920001721 polyimide Polymers 0.000 description 1
- 229920001155 polypropylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 230000001737 promoting effect Effects 0.000 description 1
- 229910021332 silicide Inorganic materials 0.000 description 1
- FVBUAEGBCNSCDD-UHFFFAOYSA-N silicide(4-) Chemical compound [Si-4] FVBUAEGBCNSCDD-UHFFFAOYSA-N 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000010409 thin film Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Description
本発明は、高安全性を指向するリチウムイオン二次電池に関し、より詳しくは短絡を回避しうる電極構造に関する。 The present invention relates to a lithium ion secondary battery oriented to high safety, and more particularly to an electrode structure capable of avoiding a short circuit.
リチウムイオン二次電池はエネルギー密度の高い蓄電池として、各種ポータブル機器の主電源として用いられている。これらの化学電池では、正極および負極と、これらの極板を電気的に絶縁しつつ電解液を保持する役目をもつセパレータがある。リチウムイオン二次電池では、現在、主にポリエチレンからなる微多孔性薄膜シートが使われており、前記正負極の間にセパレータを介在させ、捲回することにより電極群を構成している。 Lithium ion secondary batteries are used as main power sources for various portable devices as high energy density storage batteries. In these chemical batteries, there are a positive electrode and a negative electrode, and a separator having a role of holding an electrolytic solution while electrically insulating these electrode plates. At present, a microporous thin film sheet mainly made of polyethylene is used in a lithium ion secondary battery, and an electrode group is formed by winding a separator between the positive and negative electrodes.
これら樹脂からなるシート状セパレータは、釘が刺さるなどして正極と負極が電池内部で接触し、いわゆる内部短絡が発生すると、瞬時に発生する短絡反応熱によりセパレータが収縮して短絡部が拡大し、さらに多大な反応熱を発生させ、異常過熱を促進するという課題を有していた。この短絡反応熱は、リチウムを吸蔵あるいは放出して化学的ポテンシャルが高くなった正負極の合剤層が、高い導電性を示す集電体の露出部（リード集電体溶接のために設置）と短絡した場合に、最も高いことが知られている。 When these separators are made of sheet resin, the positive and negative electrodes come into contact with the inside of the battery, for example, when a nail is pierced. Furthermore, it has a problem of generating much reaction heat and promoting abnormal overheating. This short-circuit reaction heat is caused by the exposed portion of the current collector, which has a high conductivity in the positive and negative electrode mixture layers that have a high chemical potential by occlusion or release of lithium (installed for lead current collector welding). It is known that it is the highest in the case of short circuit.
この課題を解決するために、前記正負極の少なくとも一方に対し、電池群における最内周端および最外周端に位置する集電体の露出部の一部または全部に、５００℃以上の耐熱性を有する粉体をバインダ樹脂で結着してなる絶縁性被膜を固定する技術が開示されている（例えば特許文献１）。
しかしながら釘が刺さるなどの異常時を除き、実際にリチウムイオン二次電池において最も内部短絡が頻繁に発生する箇所は、正極合剤層と前記露出部との境目（以下、正極境界部と略記）である。一般に正極集電体であるアルミニウム箔は軟らかく切断が困難なため、硬く切断しやすい正極合剤層との境目で切断性のアンバランスが顕著化し、正極集電体のひげ状突出物（以降、切断バリと称す）が発生しやすい。また一般にリチウムイオン二次電池は、容量規制極である正極に対し、負極の面積を大きく設計するのが常である。よって上述した切断バリがセパレータを突き破り、対向する負極合剤層と接することにより、内部短絡が発生する。 However, the location where the internal short-circuit occurs most frequently in the lithium ion secondary battery, except when an abnormality such as a nail sticks, is the boundary between the positive electrode mixture layer and the exposed portion (hereinafter abbreviated as the positive electrode boundary portion). It is. In general, aluminum foil, which is a positive electrode current collector, is soft and difficult to cut. Therefore, the unbalance of the cutting property becomes noticeable at the boundary with the positive electrode mixture layer that is hard and easy to cut. (Called cutting burr). In general, a lithium ion secondary battery is usually designed so that the area of the negative electrode is larger than that of the positive electrode which is a capacity regulating electrode. Therefore, the above-described cutting burr breaks through the separator and comes into contact with the opposing negative electrode mixture layer, thereby generating an internal short circuit.
しかるに特許文献１の技術は、集電体上にのみ多孔膜を形成するものであり、上述した正極境界部で発生する切断バリによる内部短絡は防ぐことができない。ここで仮に正極境界部のみに樹脂テープを貼り付けた場合、この箇所での内部短絡の拡大は防げるものの、正極境界部上の切断バリが顕著な場合、正極境界部の周辺のセパレータがこの短絡箇所の発熱の影響を受けて溶融し、新たなる短絡箇所を形成して過熱する場合がある。 However, the technique of Patent Document 1 forms a porous film only on the current collector, and cannot prevent an internal short circuit due to the cutting burr generated at the positive electrode boundary described above. If the resin tape is applied only to the positive electrode boundary here, the internal short circuit can be prevented from expanding at this point, but if the cutting burr on the positive electrode boundary is noticeable, the separator around the positive electrode boundary is short-circuited. In some cases, it melts under the influence of heat generation at the location, and forms a new short-circuit location and overheats.
本発明は、前記従来の課題を解決するものであり、切断バリの発生を回避し、かつ正極境界部およびその周辺での内部短絡を防止するリチウムイオン二次電池を提供することを目的とする。 The present invention solves the above-described conventional problems, and an object of the present invention is to provide a lithium ion secondary battery that avoids the occurrence of cutting burrs and prevents internal short-circuits at the positive electrode boundary and its periphery. .
上記課題を解決するために本発明のリチウムイオン二次電池は、負極集電体上に負極合剤層を形成した帯状の負極、正極集電体上に正極合剤層を形成した帯状の正極、およびセパレータを捲回してなる電極群を有し、前記正極は、正極合剤層が存在しない正極集電体の露出部を長尺方向の少なくとも一端に有しており、かつ前記電極群の捲回方向断面に沿って、前記正極合剤層と前記露出部との境目（以下、正極境界部と略記）と平行する負極合剤層上には、耐熱性絶縁体が存在する、リチウムイオン二次電池において、前記電極群の最外周は、前記露出部で構成されており、前記耐熱性絶縁体は、前記正極境界部に外周側および内周側で対向する負極合剤層上と、前記正極境界部に外周側で対向する負極合剤層と前記負極集電体を介して表裏関係にある負極集電体面あるいは負極合剤層上とに存在することを特徴とするものである。 In order to solve the above problems, the lithium ion secondary battery of the present invention includes a strip-shaped negative electrode in which a negative electrode mixture layer is formed on a negative electrode current collector, and a strip-shaped positive electrode in which a positive electrode mixture layer is formed on a positive electrode current collector. And an electrode group formed by winding a separator, the positive electrode has an exposed portion of a positive electrode current collector in which no positive electrode mixture layer is present at at least one end in the longitudinal direction, and the electrode group A lithium ion having a heat-resistant insulator on the negative electrode mixture layer parallel to the boundary between the positive electrode mixture layer and the exposed portion (hereinafter abbreviated as the positive electrode boundary portion) along the winding cross section. In the secondary battery, the outermost periphery of the electrode group is composed of the exposed portion, and the heat-resistant insulator is on the negative electrode mixture layer facing the positive electrode boundary portion on the outer peripheral side and the inner peripheral side; The negative electrode mixture layer facing the positive electrode boundary portion on the outer peripheral side and the negative electrode current collector In which it characterized by the presence in the negative electrode current collector member surface or the negative electrode mixture layer on which a relationship.
上述した構成にすることで、正極の切断バリがセパレータを突き破り、さらに正極境界部と対向する負極合剤層上に設けた耐熱性絶縁体をも突き破った場合でも、負極合剤層上の他の箇所に設けられた耐熱性絶縁体が、短絡反応熱の影響で溶融するセパレータの代わりに正負極間の絶縁を保つため、短絡箇所が正極境界部のみに止まり、過熱を抑止できる。また前記多孔膜層を面積の大きい負極側に設けることにより、切断バリの方向性によらず、上記効果を発揮できる。 With the above-described configuration, even if the cutting burr of the positive electrode breaks through the separator and further breaks through the heat-resistant insulator provided on the negative electrode mixture layer facing the positive electrode boundary, Since the heat-resistant insulator provided at the location maintains insulation between the positive and negative electrodes instead of the separator that melts due to the effect of the short-circuit reaction heat, the short-circuit location stops only at the positive electrode boundary portion, and overheating can be suppressed. Moreover, the said effect can be exhibited irrespective of the directionality of a cutting | disconnection burr | flash by providing the said porous membrane layer in the negative electrode side with a large area.
以上のように本発明の構成を採用することにより、内部短絡が最も発生しやすい箇所およびその周辺に耐熱性を持たせることができ、リチウムイオン二次電池の信頼性を飛躍的に向上させることができる。 As described above, by adopting the configuration of the present invention, it is possible to give heat resistance to the location where the internal short circuit is most likely to occur and the vicinity thereof, and to dramatically improve the reliability of the lithium ion secondary battery. Can do.
以下、本発明を実施するための最良の形態について、図を参照しながら説明する。 The best mode for carrying out the present invention will be described below with reference to the drawings.
図１は本発明の電極群の横断面の模式図である。正極集電体１２の上に正極合剤層１１が形成された正極と、負極集電体２２の上に負極合剤層２１が形成された負極とが、セパレータ４１を介して対向するように捲回されている。すでに述べたように、容量規制極である正極に対し負極の面積を大きくするため、負極合剤層２１は正極合剤層１１の全てと対向するようになされている。 FIG. 1 is a schematic cross-sectional view of the electrode group of the present invention. The positive electrode in which the positive electrode mixture layer 11 is formed on the positive electrode current collector 12 and the negative electrode in which the negative electrode mixture layer 21 is formed on the negative electrode current collector 22 are opposed to each other through the separator 41. Has been wounded. As described above, the negative electrode mixture layer 21 faces all of the positive electrode mixture layer 11 in order to increase the area of the negative electrode relative to the positive electrode serving as the capacity regulating electrode.
正極合剤層１１は硬く切断しやすいが、一方で正極集電体１２は軟らかく切断が困難である。よって正極境界部では、切断性のアンバランスによって切断バリが発生しやすい。そこで正極境界部と外側で対向する負極合剤層２１の端部上に耐熱性絶縁体３２を、負極集電体２２を介して耐熱性絶縁体３２と表裏関係にある箇所に耐熱性絶縁体３１を、正極境界部と内側で対向する負極合剤層２１の上に耐熱性絶縁体３３を、負極集電体２２を介して耐熱性絶縁体３３と表裏関係にある箇所に耐熱性絶縁体３４をそれぞれ設けることにより、切断バリがセパレータ４１および耐熱性絶縁体３２あるいは３３を突き破り、短絡反応熱が発生して正極境界部の周辺でセパレータ４１が溶融した場合でも、耐熱性絶縁体３１あるいは３４が正負極間の絶縁を確保するため、内部短絡による過熱を回避することができる。なお図示されてはいないが、電極群の捲回方向断面に沿って、耐熱性絶縁体３４と平行する形で、捲回中心方向に沿って負極合剤層２１上に耐熱性絶縁体が連なって形成されていてもよい。 The positive electrode mixture layer 11 is hard and easy to cut, while the positive electrode current collector 12 is soft and difficult to cut. Therefore, cutting burrs are likely to occur at the positive electrode boundary due to the unbalance of cutting property. Therefore, the heat-resistant insulator 32 is provided on the end portion of the negative electrode mixture layer 21 that faces the positive electrode boundary portion on the outside, and the heat-resistant insulator is provided at a location that is in a front-back relationship with the heat-resistant insulator 32 via the negative electrode current collector 22. 31, a heat-resistant insulator 33 on the negative electrode mixture layer 21 facing the positive electrode boundary portion on the inner side, and a heat-resistant insulator at a position in front and back relation with the heat-resistant insulator 33 through the negative electrode current collector 22. By providing 34, the cutting burr breaks through the separator 41 and the heat-resistant insulator 32 or 33, and even when the short-circuit reaction heat is generated and the separator 41 is melted around the positive electrode boundary portion, the heat-resistant insulator 31 or Since 34 secures insulation between the positive and negative electrodes, overheating due to an internal short circuit can be avoided. Although not shown in the drawing, the heat-resistant insulator is continuous on the negative electrode mixture layer 21 along the winding center direction in a shape parallel to the heat-resistant insulator 34 along the winding-direction cross section of the electrode group. It may be formed.
ここで耐熱性絶縁体３１〜３４としては、イミドやポリアミドイミドでできた樹脂テープを挙げることができるが、絶縁性フィラーと少量のバインダーとで形成される多孔膜層とすることにより、この箇所にイオン伝導性を付与することができるので、上述した効果を、電池容量を損なうことなく発揮させることができる観点から好ましい。絶縁性フィラーとしては、異常昇温時の過熱を防ぐ観点から、耐熱性を高めるために無機酸化物を選択することができる。無機酸化物としては、アルミナ、チタニア、マグネシアなどを選択することができる。またバインダーとしては、正負極双方の電位下で安定な材料、例えばポリフッ化ビニリデン（以下、ＰＶＤＦと略記）やアクリルゴムなどを選択することができる。さらに多孔膜層の形成法としては、上述した絶縁性フィラーやバインダーを適量の溶媒を用いて分散した後、コンマコータやダイコータで負極上に塗布する方法が挙げられる。 Here, examples of the heat-resistant insulators 31 to 34 include resin tapes made of imide or polyamideimide, but this place can be obtained by forming a porous film layer formed of an insulating filler and a small amount of binder. Since ion conductivity can be imparted to the battery, it is preferable from the viewpoint that the above-described effects can be exhibited without impairing the battery capacity. As the insulating filler, an inorganic oxide can be selected in order to improve heat resistance from the viewpoint of preventing overheating at abnormal temperature rise. As the inorganic oxide, alumina, titania, magnesia, or the like can be selected. The binder can be selected from materials that are stable under both positive and negative potentials, such as polyvinylidene fluoride (hereinafter abbreviated as PVDF) and acrylic rubber. Further, as a method for forming the porous film layer, there may be mentioned a method in which the above-mentioned insulating filler or binder is dispersed using an appropriate amount of solvent and then coated on the negative electrode with a comma coater or a die coater.
本発明でいうところの耐熱性とは、リチウムイオン二次電池が過熱した際に達しうる温
度（具体的には１５０℃）において、成形物が目視上変形しないことを示す。
The heat resistance referred to in the present invention indicates that the molded product is not visually deformed at a temperature that can be reached when the lithium ion secondary battery is overheated (specifically, 150 ° C.).
なお耐熱性絶縁体３１〜３４は、多孔膜層のようにイオン伝導性を有するものであっても反応の抵抗成分となりうるため、図１のように電極群の捲回方向断面に沿って正極境界部と平行する位置に限定して形成されるのが好ましい。 Since the heat-resistant insulators 31 to 34 can be a resistance component of the reaction even if they have ion conductivity such as a porous membrane layer, the positive electrode along the winding direction cross section of the electrode group as shown in FIG. It is preferable to form it limited to a position parallel to the boundary portion.
図１では電極群の最外周部が正極集電体の露出部となっているが、この方が内部短絡発生時に短絡電流が拡散し、短絡反応熱が抑制されるので好ましい。よって図１のような構成の場合、耐熱性絶縁体を３１〜３３のみに限定しても、本発明の効果は十分に発揮される上に、耐熱性絶縁体の重なりによる電極群の変形と、それに伴う充放電特性の低下が起こりにくいので好ましい。 In FIG. 1, the outermost peripheral portion of the electrode group is the exposed portion of the positive electrode current collector, but this is preferable because the short-circuit current is diffused when an internal short-circuit occurs and the short-circuit reaction heat is suppressed. Therefore, in the case of the configuration as shown in FIG. 1, even if the heat-resistant insulator is limited to only 31 to 33, the effect of the present invention is sufficiently exerted, and the deformation of the electrode group due to the overlapping of the heat-resistant insulators. It is preferable because the charge / discharge characteristics are not easily lowered.
また図１では負極合剤層２１が負極の最外周外側には存在しないが、これは対向する正極合剤層１１がない箇所の合剤を削除することにより、電池を高容量化することを目論んだものである。一方生産性を重視して、この負極最外周外側に負極合剤層２１を設けても、本発明の効果は同様に発揮できる。 Further, in FIG. 1, the negative electrode mixture layer 21 does not exist on the outermost outer periphery of the negative electrode, but this means that the capacity of the battery can be increased by deleting the mixture where there is no opposing positive electrode mixture layer 11. This is what I intended. On the other hand, even if the negative electrode mixture layer 21 is provided outside the outermost periphery of the negative electrode with emphasis on productivity, the effects of the present invention can be exhibited in the same manner.
上述した本発明の骨子をなす構成要素の他に、以下に示す材料を適宜用いることができる。 In addition to the above-described constituent elements of the present invention, the following materials can be used as appropriate.
正極は活物質に複合リチウム酸化物を用いることができる。具体的には組成式ＬｉＭＯ2あるいはＬｉＭ2Ｏ4で示され、ＭとしてはＣｏ、Ｍｎ、Ｎｉ、Ｆｅをはじめとした遷移金属を少なくとも１種選択することができる。また上述した遷移金属の一部を、Ａｌ、Ｍｇなどの典型金属に置換することも可能である。 The positive electrode can use composite lithium oxide as an active material. Specifically, it is represented by a composition formula LiMO 2 or LiM 2 O 4 , and M can be selected from at least one transition metal including Co, Mn, Ni, and Fe. It is also possible to replace a part of the transition metal described above with a typical metal such as Al or Mg.
上述した正極活物質は、導電剤およびバインダーと混練され、正極ペーストとして正極芯材に塗布乾燥され、所定厚に圧延された後、所定寸法に切断されて正極となる。ここで導電剤としては、アセチレンブラック（以下、ＡＢと略記）などのカーボンブラックや、黒鉛材料、正極電位下において安定な金属微粉末を用いることができる。またバインダーとしては、正極電位下において安定な材料、例えばＰＶＤＦや変性アクリルゴム、ポリテトラフルオロエチレンなどを用いることができる。さらにはペーストを安定化させる増粘剤として、カルボキシメチルセルロース（以下、ＣＭＣと略記）などのセルロース樹脂を用いても良い。さらに正極芯材としては、正極電位下において安定な材料、一般的にはアルミニウム箔が用いられるが、これには限らない。 The positive electrode active material described above is kneaded with a conductive agent and a binder, applied and dried as a positive electrode paste on a positive electrode core material, rolled to a predetermined thickness, and then cut into a predetermined dimension to form a positive electrode. Here, as the conductive agent, carbon black such as acetylene black (hereinafter abbreviated as AB), graphite material, or metal fine powder that is stable under a positive electrode potential can be used. As the binder, a material that is stable under the positive electrode potential, such as PVDF, modified acrylic rubber, polytetrafluoroethylene, or the like can be used. Furthermore, a cellulose resin such as carboxymethyl cellulose (hereinafter abbreviated as CMC) may be used as a thickener for stabilizing the paste. Further, as the positive electrode core material, a material which is stable under the positive electrode potential, generally an aluminum foil, is used, but is not limited thereto.
負極は活物質にリチウムを吸蔵できる材料を用いることができる。具体的には黒鉛、シリサイド、チタン合金材料などから少なくとも１種を選択することができる。 For the negative electrode, a material capable of occluding lithium in the active material can be used. Specifically, at least one kind can be selected from graphite, silicide, titanium alloy material and the like.
上述した負極活物質はバインダーと混練され、負極ペーストとして負極芯材に塗布乾燥され、所定厚に圧延された後、所定寸法に切断されて負極となる。ここでバインダーとしては、負極電位下において安定な材料、例えばＰＶＤＦやスチレン−ブタジエンゴム共重合体（以下、ＳＢＲと略記）などを用いることができる。さらにはペーストを安定化させる増粘剤として、ＣＭＣなどのセルロース樹脂を用いても良い。さらに負極芯材としては、負極電位下において安定な材料、一般的には銅箔が用いられるが、これには限らない。 The negative electrode active material described above is kneaded with a binder, coated and dried as a negative electrode paste on a negative electrode core material, rolled to a predetermined thickness, and then cut into predetermined dimensions to form a negative electrode. Here, as the binder, a material that is stable under a negative electrode potential, such as PVDF or a styrene-butadiene rubber copolymer (hereinafter abbreviated as SBR) can be used. Furthermore, a cellulose resin such as CMC may be used as a thickener for stabilizing the paste. Further, as the negative electrode core material, a material that is stable under a negative electrode potential, generally a copper foil, is used, but is not limited thereto.
セパレータは電解液の保持力が高く、正負極いずれの電位下においても安定な微多孔性フィルムを用いるのが一般的である。具体的にはポリプロピレン（以下、ＰＰと略記）、ポリエチレン、ポリイミド、ポリアミドなどを用いることができる。 As the separator, it is common to use a microporous film that has a high holding power of the electrolytic solution and is stable at any potential of the positive and negative electrodes. Specifically, polypropylene (hereinafter abbreviated as PP), polyethylene, polyimide, polyamide, or the like can be used.
以下、本発明の実施例について詳述する。 Examples of the present invention will be described in detail below.
人造黒鉛１００重量部に対し、ＳＢＲを固形分で１重量部、ＣＭＣを固形分で１重量部加え、適量の水とともに双腕式練合機にて攪拌し、負極ペーストを作製した。このペースト（乾燥によって負極合剤層となる）を１０μｍ厚の銅箔（負極集電体）に塗布乾燥し、総厚が１８０μｍとなるように圧延した後、幅５５ｍｍ、長さ６２０ｍｍに切断して負極を作製した。 To 100 parts by weight of artificial graphite, 1 part by weight of SBR and 1 part by weight of CMC were added and stirred with a suitable amount of water in a double-arm kneader to prepare a negative electrode paste. This paste (which becomes a negative electrode mixture layer by drying) is applied and dried on a 10 μm thick copper foil (negative electrode current collector), rolled to a total thickness of 180 μm, and then cut to a width of 55 mm and a length of 620 mm. Thus, a negative electrode was produced.
この負極合剤層に対し、電極群を構成した際に電極群の捲回方向断面に沿って正極境界部と平行する箇所（図１の３１〜３４、および電極群の捲回方向断面に沿って３４と平行する形で捲回中心方向に沿って連綿と）に、耐熱性絶縁体として多孔膜層を一体形成した。これら多孔膜層は、平均粒子径０．５μｍのアルミナ粒子１００重量部に対し４重量部のＰＶＤＦを加え、適量のＮ−メチルピロリドン（以下、ＮＭＰと略記）とともに双腕式練合機にて攪拌した後、直径０．２ｍｍのジルコニアビーズを用いてビーズミル分散したペーストを、負極合剤層２１上に集電体露出部と平行に、１０ｍｍ幅で塗布して得た。多孔膜層の厚みは平均１０μｍであった。 With respect to this negative electrode mixture layer, when the electrode group is configured, the portion parallel to the positive electrode boundary along the winding direction cross section of the electrode group (31 to 34 in FIG. 1 and the winding direction cross section of the electrode group) A porous film layer was integrally formed as a heat-resistant insulator in a manner parallel to the winding 34 along the winding center direction. In these porous membrane layers, 4 parts by weight of PVDF is added to 100 parts by weight of alumina particles having an average particle diameter of 0.5 μm, and an appropriate amount of N-methylpyrrolidone (hereinafter abbreviated as NMP) is used in a double-arm kneader. After stirring, a paste dispersed in a bead mill using zirconia beads having a diameter of 0.2 mm was applied on the negative electrode mixture layer 21 in a width of 10 mm in parallel with the exposed portion of the current collector. The average thickness of the porous membrane layer was 10 μm.
一方、コバルト酸リチウム１００重量部に対し、ＰＶＤＦを４重量部、ＡＢを３重量部加え、適量のＮＭＰとともに双腕式練合機にて攪拌し、正極ペーストを作製した。このペースト（乾燥によって正極合剤層となる）を１５μｍ厚のアルミニウム箔（正極集電体）に塗布乾燥し、総厚が１６０μｍとなるように圧延した後、幅５３ｍｍ、長さ５５０ｍｍに切断して正極を作製した。 On the other hand, 4 parts by weight of PVDF and 3 parts by weight of AB were added to 100 parts by weight of lithium cobaltate, and the mixture was stirred with a suitable amount of NMP in a double-arm kneader to prepare a positive electrode paste. This paste (which becomes a positive electrode mixture layer by drying) is applied and dried on a 15 μm thick aluminum foil (positive electrode current collector), rolled to a total thickness of 160 μm, and then cut to a width of 53 mm and a length of 550 mm. Thus, a positive electrode was produced.
ここで正極を切断する際、２枚の切断刃の間隔を３００μｍとし、高さ８０〜１５０μｍの切断バリが正極合剤層１１の端部の切断箇所に生じるように調整した。
この正極と前述した負極とを、セパレータ（ＰＰ製微多孔性フィルム、２３μｍ厚）を介して捲回することにより電極群を得た。
Here, when the positive electrode was cut, the interval between the two cutting blades was set to 300 μm, and a cutting burr having a height of 80 to 150 μm was adjusted to occur at the cut portion at the end of the positive electrode mixture layer 11.
The positive electrode and the negative electrode described above were wound through a separator (PP microporous film, 23 μm thickness) to obtain an electrode group.
この電極群を直径１８ｍｍ、高さ６５ｍｍの円筒型有底金属缶に挿入し、ＥＣ：ＤＥＣ：ＤＭＣ＝２０：４０：４０（重量％）の溶媒にＬｉＰＦ6を１モル／リットル溶解させた電解液を加えた後、金属缶の開口部を封口し、公称容量２Ａｈのリチウムイオン二次電池を作製した。これを実施例１の電池とする。 This electrode group was inserted into a cylindrical bottomed metal can having a diameter of 18 mm and a height of 65 mm, and 1 mol / liter of LiPF 6 was dissolved in a solvent of EC: DEC: DMC = 20: 40: 40 (wt%). After the liquid was added, the opening of the metal can was sealed, and a lithium ion secondary battery having a nominal capacity of 2 Ah was produced. This is referred to as the battery of Example 1.
実施例１の正極に対し、正極集電体１２のみからなる露出部（長さ５０ｍｍ）を設けることにより正極の長さを６００ｍｍとし、この露出部が電極群の最外周をなすようにしたこと以外は、実施例１と同様の電池を作製した。これを実施例２の電池とする。 For the positive electrode of Example 1, the length of the positive electrode was set to 600 mm by providing an exposed portion (length: 50 mm) consisting only of the positive electrode current collector 12, and this exposed portion was the outermost periphery of the electrode group. A battery was manufactured in the same manner as in Example 1 except for the above. This is referred to as the battery of Example 2.
実施例２の電池に対し、多孔膜層を図１の３４に該当する箇所に設けなかったこと以外は、実施例２と同様の電池を作製した。これを実施例３の電池とする。 A battery similar to that of Example 2 was produced, except that the porous film layer was not provided at the position corresponding to 34 in FIG. This is referred to as the battery of Example 3.
実施例１の電池に対し、図１の３１〜３４に該当する箇所に設ける耐熱性絶縁体を、多孔膜層に代えて２５μｍ厚のイミド樹脂テープにしたこと以外は、実施例１と同様の電池を作製した。これを実施例４の電池とする。
（参考例）
実施例１の電池に対し、多孔膜層を図１の３１および３４に該当する箇所に設けなかったこと以外は、実施例１と同様の電池を作製した。これを参考例の電池とする。
（比較例１）
多孔膜層を設けなかった以外は、実施例１と同様の電池を作製した。これを比較例１の電池とする。
（比較例２）
実施例１の電池に対し、図１の３１〜３４に設けられた多孔膜層に代えて、２５μｍ厚のＰＰ樹脂テープにしたこと以外は、実施例１と同様の電池を作製した。これを比較例２の電池とする。
（比較例３）
実施例２の電池に対し、図１の３１〜３４に設けられた多孔膜層に代えて、２５μｍ厚のＰＰ樹脂テープにしたこと以外は、実施例２と同様の電池を作製した。これを比較例３の電池とする。
The battery of Example 1 is the same as Example 1 except that the heat-resistant insulator provided at the locations corresponding to 31 to 34 in FIG. 1 is replaced with a 25 μm thick imide resin tape instead of the porous membrane layer. A battery was produced. This is the battery of Example 4.
(Reference example)
A battery similar to that of Example 1 was produced, except that the porous film layer was not provided at locations corresponding to 31 and 34 in FIG. This is the battery of the reference example.
(Comparative Example 1)
A battery was prepared in the same manner as in Example 1 except that the porous film layer was not provided. This is referred to as the battery of Comparative Example 1.
(Comparative Example 2)
The battery of Example 1 was made in the same manner as in Example 1 except that a 25 μm thick PP resin tape was used instead of the porous membrane layer provided in 31 to 34 of FIG. This is referred to as the battery of Comparative Example 2.
(Comparative Example 3)
A battery similar to that of Example 2 was produced, except that a PP resin tape having a thickness of 25 μm was used instead of the porous film layer provided in 31 to 34 of FIG. This is referred to as the battery of Comparative Example 3.
得られた各例の電池に対し、以下の評価を行った。 The following evaluation was performed on the batteries of the obtained examples.
（短絡検査）
電池各２０個を、４００ｍＡの電流値で４．１Ｖに達するまで充電した後、４５℃環境下で７日間保存した。保存前後で開回路電圧が３００ｍＶ以上低下した電池を短絡電池とし、その割合を百分率で（表１）に示した。
(Short-circuit inspection)
Each of the 20 batteries was charged to reach 4.1 V at a current value of 400 mA, and then stored in a 45 ° C. environment for 7 days. A battery whose open circuit voltage decreased by 300 mV or more before and after storage was designated as a short-circuit battery, and the ratio was shown in Table 1 as a percentage.
（発熱温度測定）
上述した短絡検査で異常が見られた電池各１個を、室温下で４００ｍＡの電流値で３．０Ｖに達するまで放電した後、２Ａで１時間の定電流充電を行った。充電終了直後の電池表面温度を（表１）に示した。
(Exothermic temperature measurement)
Each battery in which an abnormality was found in the short-circuit inspection described above was discharged until reaching 3.0 V at a current value of 400 mA at room temperature, and then subjected to constant current charging at 2 A for 1 hour. The battery surface temperature immediately after the end of charging is shown in (Table 1).
（容量確認）
上述した短絡検査で異常が見られなかった電池各１個を、室温下で４００ｍＡの電流値で３．０Ｖに達するまで放電した。その後、以下に示す充放電を２回繰り返した。この時の２回目の放電容量を（表１）に示した。
充電：２Ａで４．２Ｖまで定電流充電後、５０ｍＡまで定電圧充電
放電：４００ｍＡで３．０Ｖまで定電流放電
(Capacity check)
Each battery in which no abnormality was found in the short-circuit inspection described above was discharged at room temperature until it reached 3.0 V at a current value of 400 mA. Thereafter, the following charge / discharge was repeated twice. The second discharge capacity at this time is shown in Table 1.
Charge: Constant current charge to 4.2V at 2A, then constant voltage charge / discharge to 50mA: Constant current discharge to 3.0V at 400mA
（ハイレート特性評価）
上述した容量確認の後、室温下で以下に示す充放電を行った。この時の放電容量を、上述した容量確認時の放電容量で除した値を、百分率で（表１）に示した。
充電：２Ａで４．２Ｖまで定電流充電後、５０ｍＡまで定電圧充電
放電：４Ａで３．０Ｖまで定電流放電
(High rate characteristic evaluation)
After the capacity check described above, the following charge / discharge was performed at room temperature. The value obtained by dividing the discharge capacity at this time by the discharge capacity at the time of the capacity check described above is shown as a percentage (Table 1).
Charging: After constant current charging to 4.2V at 2A, constant voltage charging / discharging up to 50mA: constant current discharging to 3.0V at 4A
耐熱性絶縁体を設けなかった比較例１は、意図的に設けた切断バリの影響を受けて、ほぼ全数が短絡を起こす結果となった。これに対し、耐熱性絶縁体として多孔膜層を図１の
３２および３３の箇所に設けた参考例は、上述した切断バリが負極合剤層に達する機会を減らすことにより、短絡を激減させることができた。ただし短絡電池を強制的に充電した場合、直後の電池表面温度が７８℃と比較的高い値となった。強制充電後の電池を分解したところ、切断バリが発生していた正極境界部に対向する箇所については、図１の３２および３３の箇所に設けた多孔膜層があるために短絡箇所の拡大が見られなかったが、負極集電体を介して３２および３３と表裏関係を有する箇所において、セパレータの溶融が若干ながら見られた。よって電池表面温度が比較的上昇した原因は、切断バリによって起こった短絡の反応熱が周辺のセパレータを溶融し、この箇所で短絡が拡大して比較的大きなジュール熱が発生したことであると推考できた。
In Comparative Example 1 in which the heat-resistant insulator was not provided, almost all of them were short-circuited due to the intentionally provided cutting burr. On the other hand, the reference example in which the porous film layer is provided as the heat resistant insulator at the positions 32 and 33 in FIG. 1 drastically reduces the short circuit by reducing the opportunity for the above-mentioned cutting burr to reach the negative electrode mixture layer. I was able to. However, when the short-circuit battery was forcibly charged, the battery surface temperature immediately afterwards was a relatively high value of 78 ° C. When the battery after forced charging is disassembled, the portion facing the positive electrode boundary where the cutting burr has occurred has a porous film layer provided at 32 and 33 in FIG. Although not seen, some melting of the separator was seen at a portion having a front and back relationship with 32 and 33 through the negative electrode current collector. Therefore, it can be inferred that the cause of the relatively high battery surface temperature is that the reaction heat of the short circuit caused by the cutting burr melts the surrounding separator, and the short circuit expands at this point and relatively large Joule heat is generated. did it.
この参考例に対し、本発明の実施例１〜３は短絡発生率が低いだけでなく、短絡電池を強制充電した際の電池表面温度も抑制できた。これらの電池を強制充電後に分解したところ、図１の３１および３４の箇所において、セパレータは僅かに溶融しているものの、３１および３４の箇所に設けられた多孔膜層が正負極間の絶縁を確保していることが確認できた。よって電池表面温度の上昇が抑制できた原因は、短絡箇所を切断バリが発生していた正極境界部にのみ止めることができたからであると推考できた。 In contrast to this reference example, Examples 1 to 3 of the present invention not only had a low short-circuit occurrence rate, but also suppressed the battery surface temperature when the short-circuit battery was forcibly charged. When these batteries were disassembled after forced charging, the separators were slightly melted at 31 and 34 in FIG. 1, but the porous membrane layer provided at 31 and 34 provided insulation between the positive and negative electrodes. It was confirmed that it was secured. Therefore, it was inferred that the reason why the rise in the battery surface temperature could be suppressed was that the short-circuited part could be stopped only at the positive electrode boundary where the cutting burr was generated.
ここで電極群の最外周を正極集電体の露出部とした実施例２は、実施例１よりも短絡電池の強制充電後の電池表面温度を低下させることができた。このように耐短絡性の高い構造を採った場合、実施例３のように耐熱性絶縁体を設ける場所を限定しても、短絡箇所の拡大を十分に抑止できる上、反応抵抗となる耐熱性絶縁体を少なくすることによりハイレート特性も向上するので、より好ましい。 Here, in Example 2 in which the outermost periphery of the electrode group was the exposed portion of the positive electrode current collector, the battery surface temperature after forced charging of the short-circuit battery could be lowered as compared with Example 1. Thus, when adopting a structure with high short-circuit resistance, even if the location where the heat-resistant insulator is provided as in Example 3, the expansion of the short-circuit portion can be sufficiently suppressed, and the heat resistance that becomes the reaction resistance Since the high rate characteristic is also improved by reducing the number of insulators, it is more preferable.
耐熱性絶縁体として多孔膜層に代えてイミド樹脂テープを用いた実施例４は、実施例１〜３と同様に短絡発生率を低減できる上、短絡電池における短絡箇所の拡大を抑止することができる。ただし放電容量については、イオン伝導性のないイミド樹脂テープで覆われた箇所が充放電に寄与しがたい分、低下することになる。 Example 4 using an imide resin tape instead of the porous film layer as the heat-resistant insulator can reduce the occurrence rate of short circuit similarly to Examples 1 to 3, and can suppress the expansion of the short circuit location in the short circuit battery. it can. However, the discharge capacity is reduced because the portion covered with the imide resin tape having no ion conductivity hardly contributes to charge / discharge.
また多孔膜層に代えて耐熱性の低い絶縁体であるＰＰ樹脂テープを用いた比較例２〜３は、短絡発生率こそ低下できたものの、短絡箇所の拡大は抑止できなかった。短絡電池を強制充電後に分解したところ、切断バリが発生していた正極境界部においても、ＰＰの耐熱性の低さに起因して短絡箇所の拡大が確認できた。 Moreover, although the comparative examples 2-3 using PP resin tape which is an insulator with low heat resistance instead of the porous membrane layer could reduce the short circuit occurrence rate, the expansion of the short circuit location could not be suppressed. When the short-circuit battery was disassembled after forced charging, the expansion of the short-circuit portion could be confirmed even at the positive electrode boundary where the burr was generated due to the low heat resistance of PP.
本発明により短絡不良を激減させることができる上、万が一短絡が発生した場合の安全性を高めることができるため、特に捲回状の電極群からなるリチウムイオン二次電池全般の信頼性を高める技術として、その利用可能性および有用性は高い。 The present invention can drastically reduce short-circuit defects and increase the safety in the event of a short-circuit, and in particular, a technology for improving the reliability of lithium ion secondary batteries in general consisting of wound electrode groups. As such, its availability and usefulness are high.
１１ 正極合剤層
１２ 正極集電体
２１ 負極合剤層
２２ 負極集電体
３１、３２、３３、３４ 耐熱性絶縁体
４１ セパレータ
DESCRIPTION OF SYMBOLS 11 Positive electrode mixture layer 12 Positive electrode collector 21 Negative electrode mixture layer 22 Negative electrode collector 31, 32, 33, 34 Heat resistant insulator 41 Separator
Claims (2)
前記電極群の最外周は、前記露出部で構成されており、前記耐熱性絶縁体は、前記正極合剤層と前記露出部との境目に外周側および内周側で対向する負極合剤層上と、前記正極合剤層と前記露出部との境目に外周側で対向する負極合剤層と前記負極集電体を介して表裏関係にある負極集電体面あるいは負極合剤層上とに存在することを特徴とする、リチウムイオン二次電池。 Strip-shaped anode forming a negative electrode mixture layer on the negative electrode current collector, have a strip-shaped positive electrode, and separator electrode group formed by winding the data forming the positive electrode mixture layer on the positive electrode current collector, the positive electrode Has an exposed portion of the positive electrode current collector in which no positive electrode mixture layer is present at at least one end in the longitudinal direction, and the positive electrode mixture layer and the exposed portion along a winding direction cross section of the electrode group. In the lithium ion secondary battery in which a heat-resistant insulator exists on the negative electrode mixture layer parallel to the boundary with the part ,
The outermost periphery of the electrode group is composed of the exposed portion, and the heat-resistant insulator is a negative electrode mixture layer facing on the outer peripheral side and the inner peripheral side at the boundary between the positive electrode mixture layer and the exposed portion. On the negative electrode current collector surface or the negative electrode mixture layer that are in a front-back relationship with the negative electrode mixture layer facing the outer periphery at the boundary between the positive electrode mixture layer and the exposed portion and the negative electrode current collector A lithium ion secondary battery characterized by being present.
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