JP2004214066A - Separator for lithium secondary battery, and lithium secondary battery - Google Patents
Separator for lithium secondary battery, and lithium secondary battery Download PDFInfo
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- JP2004214066A JP2004214066A JP2003000753A JP2003000753A JP2004214066A JP 2004214066 A JP2004214066 A JP 2004214066A JP 2003000753 A JP2003000753 A JP 2003000753A JP 2003000753 A JP2003000753 A JP 2003000753A JP 2004214066 A JP2004214066 A JP 2004214066A
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- separator
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- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 54
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 52
- 239000000835 fiber Substances 0.000 claims abstract description 46
- 239000004745 nonwoven fabric Substances 0.000 claims abstract description 27
- 238000002844 melting Methods 0.000 claims abstract description 21
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- 125000003118 aryl group Chemical group 0.000 claims description 6
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- 229920002614 Polyether block amide Polymers 0.000 claims description 3
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- 239000004693 Polybenzimidazole Substances 0.000 claims description 2
- 150000002641 lithium Chemical class 0.000 abstract 1
- 238000000034 method Methods 0.000 description 16
- 239000003792 electrolyte Substances 0.000 description 7
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- 239000012943 hotmelt Substances 0.000 description 5
- 229920000642 polymer Polymers 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 239000002033 PVDF binder Substances 0.000 description 4
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- 230000000052 comparative effect Effects 0.000 description 4
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- 229910052782 aluminium Inorganic materials 0.000 description 3
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- YEJRWHAVMIAJKC-UHFFFAOYSA-N 4-Butyrolactone Chemical compound O=C1CCCO1 YEJRWHAVMIAJKC-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 2
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- 229910012851 LiCoO 2 Inorganic materials 0.000 description 2
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- 229910017052 cobalt Inorganic materials 0.000 description 1
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- 229910002804 graphite Inorganic materials 0.000 description 1
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- 239000001989 lithium alloy Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910001510 metal chloride Inorganic materials 0.000 description 1
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- 229910052976 metal sulfide Inorganic materials 0.000 description 1
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- 239000004763 nomex Substances 0.000 description 1
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- 229920005606 polypropylene copolymer Polymers 0.000 description 1
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- 238000002411 thermogravimetry Methods 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
- 239000004711 α-olefin Substances 0.000 description 1
Classifications
-
- 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
Landscapes
- Cell Separators (AREA)
- Secondary Cells (AREA)
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明はリチウム二次電池用セパレータ及びリチウム二次電池に関する。
【０００２】
【従来の技術】
リチウム二次電池内で短絡が生じると、電池内部における温度が急上昇し、内圧が高くなる結果、電解液が噴出する可能性があるため、リチウム二次電池内で短絡しないセパレータが提案されている。
【０００３】
例えば、大部分の繊維径が１０μｍ以下である繊維ウエブからなる微孔を有する繊維シートの少なくとも片面に１２０℃以下で溶融して流動する電気絶縁性の接着樹脂が付着した、電気抵抗が１×１０−２Ω・ｄｍ２／枚のセパレータが提案されている（例えば、特許文献１）。より具体的には、実施例として、大部分が４〜８μであるポリプロピレン繊維からなる繊維ウエブを圧着させた微孔性シートに低融点ポリエチレンのエマルジョンを含浸し、乾燥したセパレータが提案されている。しかしながら、ポリプロピレン繊維のようなポリオレフィン系繊維からなる微孔性シートを用いているため、１８０℃を超えるような高温にまで温度が上昇した場合には、微孔シート自体が溶融してしまい、十分な短絡防止機能を発揮できないものであった。また、温度の上昇とともに、セパレータの幅方向に熱収縮して幅方向の寸法が小さくなり、セパレータの幅方向端部と接触していた電極が露出してしまい、短絡を引き起す懸念があった。
【０００４】
また、１８０℃を超えるような高温にまで温度が上昇しても熱収縮の生じないセパレータとして、全芳香族ポリアミドの重合体からなるセパレータが提案されている（特許文献２）。しかしながら、このセパレータは電池自体の制御回路によって電流遮断するものであり、セパレータによるイオンの透過停止機能（いわゆるシャットダウン機能）を有していないため、リチウム二次電池の構造を複雑化し、どのようなリチウム二次電池についても適用できるものではなかった。
【０００５】
【特許文献１】
特開昭６０−１３６１６１号公報（特許請求の範囲、第２頁左上欄第４行〜第８行、実施例１など）
【特許文献２】
特開平５−３３５００５号公報（特許請求の範囲、段落番号００１１、実施例１など）
【０００６】
【発明が解決しようとする課題】
本発明は上記課題を解決するためになされたものであり、高温になっても形態を維持できることによって電極間の短絡を防止することができ、しかもシャットダウン機能を有する、汎用性に優れるリチウム二次電池用セパレータ、及びリチウム二次電池を提供することを目的とする。
【０００７】
【課題を解決するための手段】
前記課題は、「融解温度又は炭化温度が３００℃以上の樹脂からなる耐熱性繊維と、融解温度が１００〜１８０℃の熱溶融性樹脂材料とを含む不織布からなることを特徴とするリチウム二次電池用セパレータ」により解決できる。融解温度又は炭化温度が３００℃以上の樹脂からなる耐熱性繊維を含んでいるため、１８０℃を超えるような高温に温度が上昇したとしても、リチウム二次電池用セパレータが溶融して大きな穴が開いたり、収縮することがないため、電極の露出による短絡を引き起こさない。また、融解温度が１００〜１８０℃の熱溶融性樹脂材料を含んでいるため、リチウム二次電池内部の温度上昇によって熱溶融性樹脂材料が溶解し、リチウム二次電池用セパレータの空隙を閉塞できる。これにより、リチウム二次電池の内部対抗が上昇し、電流が流れにくくなったり、電流が遮断されてシャットダウン機能を発現するため、種々のリチウム二次電池に適用できる。
【０００８】
前記耐熱性繊維がパルプ形状又はチョップドファイバー形状からなると、セパレータである不織布が、均一で緻密な構造を採ることができ、短絡防止性と電解液の保持性に優れている。
【０００９】
前記耐熱性繊維が、全芳香族ポリアミド、全芳香族ポリエステル、ポリアミドイミド、芳香族ポリエーテルアミド、ポリベンゾイミダゾールの中から選ばれる樹脂からなると、特に耐熱性に優れ、リチウム二次電池が１８０℃を超えるような高温に温度が上昇したとしても、収縮することがないため、電極の露出による短絡を効果的に引き起こさない。
【００１０】
前記熱溶融性樹脂材料がチョップドファイバー形状、パルプ形状、粒子状の中から選ばれる形状からなると、セパレータである不織布内に、均一に分散することができるため、安定したシャットダウン機能を発現できる。
【００１１】
前記熱溶融性樹脂材料がポリオレフィン系樹脂からなると、耐電解液性に優れているため、安定したシャットダウン機能を発現できる。
【００１２】
本発明のリチウム二次電池は、上記いずれかに記載のリチウム二次電池用セパレータを備えているため、電解液の噴出する恐れのないものである。
【００１３】
【発明の実施の形態】
本発明のリチウム二次電池用セパレータ（以下、単に「セパレータ」という）は、電池内の温度が１８０℃を超えるような高温になったとしても、セパレータが溶融して大きな穴が開いたり、収縮せず、電極の露出による短絡を引き起こさないように、融解温度又は炭化温度が３００℃以上の樹脂からなる耐熱性繊維を含んでいる。なお、本発明における「融解温度」は、ＪＩＳ Ｋ ７１２１に規定されている示差熱分析により得られる示差熱分析曲線（ＤＴＡ曲線）から得られる温度をいい、「炭化温度」は、ＪＩＳ Ｋ ７１２０に規定されている熱重量測定により得られる温度をいう。
【００１４】
本発明の耐熱性繊維は融解温度又は炭化温度が３００℃以上の樹脂から構成されていれば良く、特に限定するものではないが、例えば、全芳香族ポリアミド、全芳香族ポリエステル、ポリアミドイミド、芳香族ポリエーテルアミド、ポリベンゾイミダゾールの中から選ばれる樹脂からなる耐熱性繊維を使用することができる。なお、耐熱性繊維は１種類であっても、２種類以上が混在していても良い。
【００１５】
なお、耐熱性繊維の形状は特に限定するものではないが、例えば、パルプ形状又はチョップドファイバー形状であることができる。前者の「パルプ形状」とは、基幹部からフィブリルが派生した状態にある繊維であり、不織布、つまりセパレータの緻密性を向上できるという特長があり、後者の「チョップドファイバー形状」とは、フィブリルの派生していない繊維であり、不織布、つまりセパレータの機械的強度を向上できるという特長がある。なお、本発明のセパレータは形状及び／又は構成樹脂の異なる耐熱性繊維が混在していても良い。
【００１６】
また、耐熱性繊維の形状がパルプ形状である場合には、セパレータが緻密な構造で、短絡防止性に優れるように、濾水度（ＣＦＳ＝カナディアンフリーネススタンダード）が２００ｍＬ以下であるのが好ましく、１５０ｍＬ以下であるのがより好ましい。他方、耐熱性繊維の形状がチョップドファイバー形状である場合には、セパレータの機械的強度に優れるように、繊維長（ＪＩＳ Ｌ １０１５（化学繊維ステープル試験法）Ｂ法（補正ステープルダイヤグラム法））は０．１〜２５ｍｍであるのが好ましく、０．２５〜２０ｍｍであるのがより好ましい。
【００１７】
このような耐熱性繊維は、電池内の温度が１８０℃を超えるような高温になったとしても、セパレータが溶融して大きな穴が開いたり、収縮せず、電極の露出による短絡を引き起こさないように、セパレータ全体の質量の３５％以上を占めているのが好ましく、５０％以上を占めているのがより好ましい。他方、後述の熱溶融性樹脂材料との兼ね合いから９０％以下であるのが好ましく、７０％以下であるのがより好ましい。
【００１８】
本発明のセパレータは上述のような耐熱性繊維に加えて、融解温度が１００〜１８０℃の熱溶融性樹脂材料を含んでいることによって、電池内部の温度上昇によって熱溶融性樹脂材料が溶解し、セパレータの空隙を閉塞できるため、リチウム二次電池の内部対抗を上昇させ、電流が流れにくくしたり、電流を遮断して、シャットダウン機能を発現することができる。
【００１９】
このような熱溶融性樹脂材料は融解温度が１００〜１８０℃の範囲内にあるものであれば良く、特に限定するものではないが、耐電解液性に優れ、しかもシャットダウン機能を発現しやすいポリオレフィン系樹脂を用いるのが好ましい。このポリオレフィン系樹脂として、例えば、高密度、中密度、低密度ポリエチレン、直鎖状低密度ポリエチレンなどのエチレン系重合体、ポリプロピレン、プロピレンと他のα−オレフィンとの共重合体（具体的にはプロピレン−ブテン−１ランダム共重合体、プロピレン−エチレン−ブテン−１ランダム共重合体など）などのプロピレン系重合体、などを挙げることができる。なお、熱溶融性樹脂材料は１種類であっても、２種類以上が混在していても良い。
【００２０】
本発明の熱溶融性樹脂材料はどのような形状からなっていても良く、特に限定するものではないが、例えば、パルプ形状、チョップドファイバー形状、粒子状などを挙げることができる。「パルプ形状」は、基幹部からフィブリルが派生した状態にあり、不織布、つまりセパレータの緻密性を向上できるという特長があり、「チョップドファイバー形状」は、フィブリルの派生していない状態にあり、不織布、つまりセパレータの機械的強度を向上できるという特長があり、「粒子状」は、繊維のように長く延びておらず、球形、直方体、立方体、円柱形、角柱形、ラグビーボール形、顆粒状などの形状を有し、不織布、つまりセパレータの緻密性を向上させ、粒子状熱溶融性樹脂材料の溶融により、より微細な空間を効果的に閉塞できるため、シャットダウン機能が向上する。なお、本発明のセパレータは形状及び／又は構成樹脂の異なる熱溶融性樹脂材料が混在していても良い。
【００２１】
また、熱溶融性樹脂材料の形状がパルプ形状である場合には、セパレータが緻密な構造で、短絡防止性に優れるように、濾水度（ＣＦＳ＝カナディアンフリーネススタンダード）が７００ｍＬ以下であるのが好ましく、４５０ｍＬ以下であるのがより好ましい。熱溶融性樹脂材料の形状がチョップドファイバー形状である場合には、セパレータの機械的強度に優れるように、繊維長（ＪＩＳ Ｌ １０１５（化学繊維ステープル試験法）Ｂ法（補正ステープルダイヤグラム法））は０．１〜２５ｍｍであるのが好ましく、０．２５〜２０ｍｍであるのがより好ましい。熱溶融性樹脂材料の形状が粒子状である場合には、セパレータの緻密性と、シャットダウン機能が向上するように、平均粒子径は１０μｍ以下であるのが好ましく、６μｍ以下であるのがより好ましい。
【００２２】
なお、この平均粒子径は数平均粒子径をいう。この数平均粒子径は、粒子状熱溶融性樹脂材料を走査型電子顕微鏡で拡大して撮影し、任意の５００個以上の粒子状熱溶融性樹脂材料の粒子径を測定した後に、これら粒子状熱溶融性樹脂材料の粒子径から算出した算術平均値をいう。なお、粒子状熱溶融性樹脂材料が球形でない場合には、個々の粒子状熱溶融性樹脂材料の外接円の直径を、個々の粒子状熱溶融性樹脂材料の粒子径とみなす。なお、市販されている粒子状熱溶融性樹脂材料の場合、カタログや仕様書に数平均粒子径が明示されている場合はその値を平均粒子径としても良い。
【００２３】
このような熱溶融性樹脂材料は、電池内部の温度上昇によって溶解し、セパレータの空隙を閉塞できるように、セパレータ全体の質量の１０％以上を占めているのが好ましく、３０％以上を占めているのがより好ましい。他方、前述の耐熱性繊維との兼ね合いから６５％以下であるのが好ましく、５０％以下であるのがより好ましい。
【００２４】
本発明のセパレータは上述のような耐熱性繊維と熱溶融性樹脂材料とを含む不織布からなるが、耐熱性繊維及び熱溶融性樹脂材料の均一分散性に優れ、短絡が発生しにくい、信頼性の高いセパレータであることができるように、湿式不織布からなるのが好ましい。
【００２５】
本発明のセパレータの構成材料（例えば、耐熱性繊維、熱溶融性樹脂材料など）は、いずれも熱融着していないのが好ましい。このように熱融着していないことによって皮膜を形成しておらず、イオンの透過性に優れているため、リチウム二次電池の通常使用時における起電作用を円滑に行うことができる。
【００２６】
本発明のセパレータ、つまり不織布の厚さはイオン透過性に優れるように、３０μｍ以下であるのが好ましく、１５〜２５μｍであるのがより好ましい。なお、セパレータの目付は５〜２０ｇ／ｍ２であるのが好ましく、見掛密度は０．１〜１．３ｇ／ｃｍ３であるのが好ましい。この「厚さ」は、ＪＩＳ Ｂ ７５０２：１９９４に規定されている外側マイクロメーター（０〜２５ｍｍ）を用いて、ＪＩＳ Ｃ２１１１ ５．１（１）の測定法で、無作為に選んで測定した１０点の平均値をいい、「目付」とは、ＪＩＳ Ｐ ８１２４（紙及び板紙−坪量測定法）に規定されている方法に基づいて得られる坪量を意味し、「見掛密度」は目付（ｇ／ｃｍ２）を厚さ（ｃｍ）で除して算出される値をいう。
【００２７】
本発明のセパレータは常法により不織布を製造し、その不織布をセパレータとして使用することができる。例えば、好適である湿式不織布は次のようにして製造することができる。
【００２８】
まず、少なくともパルプ形状の耐熱性繊維と熱溶融性樹脂材料とを用意する。これら材料は市販されているため、容易に入手することができる。
【００２９】
次いで、少なくとも耐熱性繊維と熱溶融性樹脂材料を使用して、常法の湿式法（例えば、水平長網方式、傾斜ワイヤー型短網方式、円網方式、又は長網・円網コンビネーション方式など）により湿式繊維ウエブを形成する。
【００３０】
次いで、この湿式繊維ウエブを乾燥し、水分を除去して湿式不織布、つまり本発明のセパレータを得ることができる。なお、乾燥温度は湿式繊維ウエブを構成する熱溶融性樹脂材料が融解しない温度で実施するのが好ましい。
【００３１】
このように製造した湿式不織布はセパレータとして使用することができるが、カレンダーなどによって湿式不織布に圧力を加えるのが好ましい。このように圧力を加えることによって、湿式不織布（つまりセパレータ）の厚さを調整したり、厚さを薄くしたり、厚さを均一化することができる。
【００３２】
なお、圧力を加える際には加熱しても良いし加熱しなくても良いが、加熱すると前記効果を発揮しやすい。但し、熱溶融性樹脂材料が溶融する程に加熱すると、皮膜が形成されてイオン透過性が悪くなるため、加熱する場合には、湿式不織布を構成する樹脂のうち、最も低い融解温度を有する樹脂の融解温度よりも２０℃以上低い温度で加熱するのが好ましく、３０℃以上低い温度で加熱するのがより好ましい。
【００３３】
上述の方法は、耐熱性繊維としてパルプ形状のものを使用し、耐熱性繊維のフィブリルを利用して形態を維持した湿式不織布の製造方法であるが、耐熱性繊維がチョップドファイバー形状の場合には、溶融しないものの圧力により接着可能な繊維（例えば、未延伸繊維）、又はパルプ形状の耐熱性繊維と混合して湿式繊維ウエブを形成し、前者の場合には圧力により圧着、後者の場合には耐熱性繊維のフィブリルを利用して、湿式不織布を製造することができる。
【００３４】
本発明のリチウム二次電池は前述のような本発明のセパレータを使用したものである。したがって、セパレータのシャットダウン機能によって、電池内が異常な高温となることがないため、電解液の噴出する恐れのないものである。
【００３５】
本発明のリチウム二次電池の形状は特に限定するものではないが、例えば、円筒型、角型、コイン型などであることができる。
【００３６】
本発明のリチウム二次電池は、本発明のセパレータを使用していること以外は、従来のリチウム二次電池と全く同様の材料から構成することができる。
【００３７】
例えば、正極材料（正極活物質）としては、リチウム含有金属酸化物、硫化物又は塩化物のようなリチウム含有金属化合物を使用できる。リチウム含有金属酸化物としては、例えばコバルト、マンガン、ニッケル、クロム、鉄およびバナジウムからなる群より選ばれる少なくとも１種類以上の金属とリチウムとのリチウム複合酸化物を使用できる。このようなリチウム複合酸化物としては、例えば、ＬｉＣｏＯ２、ＬｉＭｎ２Ｏ４、ＬｉＮｉＯ２などを挙げることができる。
【００３８】
正極は、前記の正極材料をアセチレンブラック、カーボンブラックなどの導電剤およびポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などの結着剤と混練して正極合剤とした後、この正極合剤を集電体としてのアルミニウム箔やステンレス製のラス板に塗布・乾燥し、加圧成型した後、５０℃〜２５０℃程度の温度で、２時間程度真空下で加熱処理して作製できる。
【００３９】
負極（負極活物質）としては、リチウム金属やリチウム合金、及びリチウムを吸蔵・放出可能なカーボン又はグラファイトを含む炭素材料、例えばコークス、天然黒鉛や人造黒鉛などの炭素材料、複合スズ酸化物を使用できる。なお、粉末状の炭素材料はエチレンプロピレンジエンターポリマー（ＥＰＤＭ）、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶＤＦ）などの結着剤と混練して負極合剤として使用できる。
【００４０】
非水電解液としては、例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ジメチルカーボネート、メチルエチルカーボネート、ジエチルカーボネート、γ−ブチロラクトン、アセトニトリル、１，２−ジメトキシエタン、テトラヒドロフラン等の有機溶媒に電解質を溶解したものを使用できる。電解質としては、例えば、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４、ＣＦ３ＳＯ３Ｌｉ、（ＣＦ３ＳＯ２）２ＮＬｉ、（Ｃ２Ｆ５ＳＯ２）２ＮＬｉ、ＬｉＣ（ＳＯ２ＣＦ３）３などを挙げることができる。これらの電解質は、１種類で使用してもよく、２種類以上組み合わせて使用してもよい。これら電解質は、前記の有機溶媒に通常０．１〜３Ｍ、好ましくは０．５〜１．５Ｍの濃度で溶解させて使用する。
【００４１】
上記構成部材を使用するリチウム二次電池の製造は、特に限定されないが、例えばコイン型リチウム二次電池は、以下の方法により製造できる。
【００４２】
まず、負極として、負極活物質をＰｖｄｆ−ＮＭＰ（ポリフッ化ビニリデン−Ｎ−メチルピロリドン）などの溶液に混合して形成した負極合剤のペーストを、銅箔上に塗布し、乾燥し、加圧成型した後に、加熱処理して負極を調製する。
【００４３】
また、正極として、リチウム複合酸化物、導電剤、及びＰｖｄｆ−ＮＭＰなどの溶液に混合して形成した正極合剤のペーストを、アルミニウム箔上に塗布し、乾燥し、加圧成型した後に、加熱処理して正極を調製する。
【００４４】
次いで、本発明のセパレータを負極と正極との間に介在させた複数のユニットと、有機溶媒に電解質を溶解させた非水電解液とを外装缶に装填して、コイン型のリチウム二次電池を作製できる。
【００４５】
以下に、本発明の実施例を記載するが、本発明は以下の実施例に限定されるものではない。
【００４６】
【実施例】
（実施例１）
耐熱性繊維として、パルプ形状を有するパラ系全芳香族ポリアミド繊維（登録商標：ケブラー、デュポン製、炭化温度：５００℃以上、濾水度（ＣＦＳ）：１２３ｍＬ）と、熱溶融性樹脂材料として、高密度ポリエチレンパルプ（登録商標：ＳＷＰ、製品名：Ｅ６２０、三井石油化学工業製、融解温度：１３０〜１３５℃、濾水度（ＣＦＳ）：３００ｍＬ）を用意した。
【００４７】
次いで、前記パラ系全芳香族ポリアミド繊維と高密度ポリエチレンパルプとを５０：５０の質量比率で混合したスラリーを調整した後、傾斜ワイヤー型短網、順流円網２台、及びヤンキードライヤーを備えた抄紙機へ前記スラリーを供給し、円網ウエブ、短網ウエブ、円網ウエブの順に抄き合わされた抄合積層湿潤ウエブを形成し、続いて、この抄合積層湿潤ウエブを温度１１０℃に設定したヤンキードライヤーへ供給して乾燥し、抄合積層乾燥ウエブを形成した。
【００４８】
次いで、得た抄合積層乾燥ウエブを、温度８０℃に設定した一対の熱カレンダーにより押圧（線圧力：４４Ｎ／ｃｍ）して、目付が１５ｇ／ｍ２で、厚さが２５μｍで、見掛密度が０．６３ｇ／ｃｍ３の押圧湿式不織布、つまりセパレータを製造した。このセパレータにおいては、パラ系全芳香族ポリアミド繊維と高密度ポリエチレンパルプのいずれも熱融着していなかった。
【００４９】
（実施例２）
耐熱性繊維として、パルプ形状を有するパラ系全芳香族ポリアミド繊維（登録商標：ケブラー、デュポン製、炭化温度：５００℃以上、濾水度（ＣＦＳ）：１２３ｍＬ）と、熱溶融性樹脂材料として、高密度ポリエチレン粒子（登録商標：フロービーズ、製品名：ＬＥ−１０８０、住友精化株式会社製、融解温度：１３０〜１３５℃、平均粒子径：６μｍ）を用意した。
【００５０】
次いで、前記パラ系全芳香族ポリアミド繊維と高密度ポリエチレン粒子とを５０：５０の質量比率で混合したスラリーを調整したこと以外は、実施例１と全く同様にして、抄合積層乾燥ウエブを形成した後に、一対の熱カレンダーにより押圧（線圧力：４４Ｎ／ｃｍ）して、目付が１５ｇ／ｍ２で、厚さが２５μｍで、見掛密度が０．６３ｇ／ｃｍ３の押圧湿式不織布、つまりセパレータを製造した。このセパレータにおいては、パラ系全芳香族ポリアミド繊維と高密度ポリエチレン粒子のいずれも熱融着していなかった。
【００５１】
（比較例１）
全芳香族ポリアミドの重合体であるアラミド繊維の隙間に、全芳香族ポリアミドの重合体である合成パルプが分散した構造を有する、通気性のある紙様シート（ノーメックス紙、タイプ４１１、デュポン社製、公称厚さ：０．１２７ｍｍ、目付：３９ｇ／ｍ２、乾燥時の平均密度：０．２８ｇ／ｃｍ３）をセパレータとした。
【００５２】
（比較例２）
メルトブロー法により、大部分の繊維の繊維径が４〜８μｍであるポリプロピレン繊維ウエブをコンベア上に形成した後、直ちに９０℃に加熱し、リアイアントプレスで圧着して、目付が３５ｇ／ｍ２で、厚さが６５μｍの圧着繊維ウエブを形成した。
【００５３】
次いで、この圧着繊維ウエブに、低密度ポリエチレン（融点：１１０℃）のエマルジョンを含浸し、乾燥して、固形分で低密度ポリエチレンが７ｇ／ｍ２付着した接着不織布を形成し、この接着不織布をセパレータとした。
【００５４】
（比較例３）
実施例１において使用したパラ系全芳香族ポリアミド繊維を１００％使用したこと以外は、実施例１と全く同様にして、抄合積層乾燥ウエブの形成、一対の熱カレンダーによる押圧を実施して、目付が２０ｇ／ｍ２で、厚さが２５μｍで、見掛密度が０．８ｇ／ｃｍ３の押圧湿式不織布、つまりセパレータを製造した。このセパレータにおいては、パラ系全芳香族ポリアミド繊維は熱融着していなかった。
【００５５】
（リチウム二次電池の作製）
まず、メソフェーズ小球体を黒鉛化したものと、Ｐｖｄｆ−ＮＭＰ（ポリフッ化ビニリデン−Ｎ−メチルピロリドン：１３重量％）溶液を、固形分の質量比９０：１０で混合したペーストを、銅箔上に塗布・乾燥し、加圧成型した後に加熱処理して負極を調製した。
【００５６】
また、正極として、ＬｉＣｏＯ２：アセチレンブラック：Ｐｖｄｆ−ＮＭＰ溶液（１２重量％）を、固形分の質量比８５：５：１０で混合したペーストを、アルミニウム箔上に塗布・乾燥し、加圧成型した後に加熱処理して正極を調製した。
【００５７】
次いで、セパレータとして、実施例１〜２及び比較例１〜３のセパレータをそれぞれ用い、エチレンカーボネート／ジエチルカーボネートを体積比で１：１で混合した溶媒に、１ｍｏｌ／ＬのＬｉＰＦ６を溶解させた非水電解液を用意し、前記セパレータを負極と正極との間に介在させた複数のユニットと、前記非水電解液とを外装缶に装填して、コイン型のリチウム二次電池（直径：２０ｍｍ、厚さ：３．２ｍｍ）を作製した。
【００５８】
（内部抵抗の測定）
上記方法により製造したコイン型リチウム二次電池の、温度２０℃における内部抵抗（初期抵抗値）を１ｋＨｚで測定した。
【００５９】
次いで、このコイン型リチウム二次電池を防爆ドライヤー内に設置した熱板上に置き、温度２０℃から２００℃まで、５℃／分の速度で昇温させた。この過程で温度１３０℃及び２００℃における内部抵抗を測定した。これらの結果は表１に示す通りであった。
【００６０】
【表１】
【００６１】
この表１から明らかなように、実施例１及び２の本発明のセパレータにおいては、１３０℃における内部抵抗が上昇していることから、シャットダウン機能が作用していることが類推できるものであった。これは、セパレータを構成する熱溶融性樹脂材料の溶融によるものであると考えられた。
【００６２】
また、実施例１及び２の本発明のセパレータは、２００℃の高温に晒しても、電池が発熱し、電解液が噴出して破損することなく、内部抵抗を測定できた。したがって、セパレータが溶融したり、収縮していないことが類推できるものであった。
【００６３】
【発明の効果】
本発明のリチウム二次電池用セパレータは、１８０℃を超えるような高温に温度が上昇したとしても、リチウム二次電池用セパレータが溶融して大きな穴が開いたり、収縮することがないため、電極の露出による短絡を引き起こさない。また、シャットダウン機能を発現できるため、種々のリチウム二次電池に適用できる。
【００６４】
本発明のリチウム二次電池は、電解液の噴出する恐れのないものである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a lithium secondary battery separator and a lithium secondary battery.
[0002]
[Prior art]
When a short circuit occurs in the lithium secondary battery, the temperature inside the battery rises sharply, and as a result, the internal pressure increases. .
[0003]
For example, an electrically insulating adhesive resin that melts and flows at 120 ° C. or less is attached to at least one surface of a fiber sheet having micropores made of a fiber web having a fiber diameter of 10 μm or less. A separator of 10 −2 Ω · dm 2 / sheet has been proposed (for example, Patent Document 1). More specifically, as an example, there has been proposed a separator in which a microporous sheet in which a fiber web made of polypropylene fibers, which is mostly 4 to 8 μm, is pressed and impregnated with a low-melting-point polyethylene emulsion and dried. . However, since a microporous sheet made of a polyolefin fiber such as a polypropylene fiber is used, if the temperature rises to a high temperature exceeding 180 ° C., the microporous sheet itself melts, and A short-circuit prevention function cannot be exhibited. Further, as the temperature rises, the separator shrinks in the width direction due to heat, and the dimension in the width direction is reduced, and the electrode that has been in contact with the width direction end of the separator is exposed, which may cause a short circuit. .
[0004]
Further, a separator made of a wholly aromatic polyamide polymer has been proposed as a separator that does not cause heat shrinkage even when the temperature is raised to a high temperature exceeding 180 ° C. (Patent Document 2). However, since this separator interrupts the current by the control circuit of the battery itself, and does not have a function of stopping the permeation of ions by the separator (so-called shutdown function), the structure of the lithium secondary battery becomes complicated, It was not applicable to lithium secondary batteries.
[0005]
[Patent Document 1]
JP-A-60-136161 (Claims, page 2, upper left column, lines 4-8, Example 1, etc.)
[Patent Document 2]
JP-A-5-335005 (Claims, paragraph number 0011, Example 1, etc.)
[0006]
[Problems to be solved by the invention]
The present invention has been made in order to solve the above-mentioned problem, and can prevent a short circuit between electrodes by maintaining a shape even at a high temperature, and has a shutdown function, and is excellent in versatility. It is an object to provide a battery separator and a lithium secondary battery.
[0007]
[Means for Solving the Problems]
The object is to provide a lithium secondary battery comprising a non-woven fabric containing a heat-resistant fiber made of a resin having a melting temperature or a carbonization temperature of 300 ° C or higher and a hot-melt resin material having a melting temperature of 100 to 180 ° C. It can be solved by a "battery separator". Since the melting temperature or the carbonization temperature includes heat-resistant fibers made of a resin having a temperature of 300 ° C. or higher, even if the temperature rises to a high temperature exceeding 180 ° C., the lithium secondary battery separator melts and large holes are formed. Since it does not open or shrink, it does not cause a short circuit due to exposure of the electrode. In addition, since the heat-melting resin material having a melting temperature of 100 to 180 ° C. is included, the heat-meltable resin material is melted by the temperature rise inside the lithium secondary battery, and the voids of the lithium secondary battery separator can be closed. . Thereby, the internal opposition of the lithium secondary battery increases, and it becomes difficult for the current to flow, or the current is cut off to exhibit a shutdown function, so that the present invention can be applied to various lithium secondary batteries.
[0008]
When the heat-resistant fiber has a pulp shape or a chopped fiber shape, the nonwoven fabric as a separator can have a uniform and dense structure, and is excellent in short-circuit prevention and electrolyte solution retention.
[0009]
When the heat-resistant fiber is made of a resin selected from a wholly aromatic polyamide, a wholly aromatic polyester, a polyamideimide, an aromatic polyetheramide, and a polybenzimidazole, the heat resistance fiber is particularly excellent in heat resistance and the lithium secondary battery has a temperature of 180 ° C. Even if the temperature rises to such a high temperature as to exceed the limit, no shrinkage occurs, so that a short circuit due to exposure of the electrode is not effectively caused.
[0010]
When the heat-fusible resin material has a shape selected from a chopped fiber shape, a pulp shape, and a particle shape, the heat-meltable resin material can be uniformly dispersed in the nonwoven fabric serving as a separator, so that a stable shutdown function can be exhibited.
[0011]
When the heat-fusible resin material is made of a polyolefin-based resin, it has excellent electrolytic solution resistance, and can exhibit a stable shutdown function.
[0012]
Since the lithium secondary battery of the present invention includes the separator for a lithium secondary battery according to any one of the above, there is no possibility that the electrolyte solution is ejected.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The separator for a lithium secondary battery of the present invention (hereinafter, simply referred to as a “separator”) is capable of forming a large hole or shrinking even if the temperature inside the battery becomes high, such as exceeding 180 ° C. In order not to cause a short circuit due to the exposure of the electrode, a heat-resistant fiber made of a resin having a melting temperature or a carbonization temperature of 300 ° C. or more is included. In the present invention, the “melting temperature” refers to a temperature obtained from a differential thermal analysis curve (DTA curve) obtained by a differential thermal analysis defined in JIS K 7121, and the “carbonization temperature” corresponds to JIS K 7120. It refers to the temperature obtained by the specified thermogravimetry.
[0014]
The heat-resistant fiber of the present invention may be composed of a resin having a melting temperature or a carbonization temperature of 300 ° C. or higher, and is not particularly limited. For example, a wholly aromatic polyamide, a wholly aromatic polyester, a polyamideimide, an aromatic Heat-resistant fibers made of a resin selected from the group consisting of polyether amides and polybenzimidazoles can be used. The heat-resistant fiber may be of one type or two or more types may be mixed.
[0015]
The shape of the heat-resistant fiber is not particularly limited, but may be, for example, a pulp shape or a chopped fiber shape. The former `` pulp shape '' is a fiber in which fibrils are derived from the backbone, and has the feature that the denseness of the nonwoven fabric, that is, the separator, can be improved.The latter `` chopped fiber shape '' is the fibril shape. It is a fiber that is not derived and has the feature that the mechanical strength of the nonwoven fabric, ie, the separator, can be improved. The separator of the present invention may contain heat-resistant fibers having different shapes and / or constituent resins.
[0016]
When the shape of the heat-resistant fiber is a pulp shape, it is preferable that the freeness (CFS = Canadian Freeness Standard) is 200 mL or less so that the separator has a dense structure and has excellent short-circuit prevention properties. More preferably, it is 150 mL or less. On the other hand, when the shape of the heat-resistant fiber is a chopped fiber shape, the fiber length (JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method)) is set so that the mechanical strength of the separator is excellent. It is preferably from 0.1 to 25 mm, more preferably from 0.25 to 20 mm.
[0017]
Such a heat-resistant fiber does not cause a short circuit due to electrode exposure even when the temperature inside the battery is raised to a temperature higher than 180 ° C. Preferably, it occupies 35% or more of the mass of the entire separator, more preferably 50% or more. On the other hand, the content is preferably 90% or less, more preferably 70% or less, in view of the balance with a heat-fusible resin material described later.
[0018]
The separator of the present invention contains a heat-meltable resin material having a melting temperature of 100 to 180 ° C. in addition to the heat-resistant fiber as described above, so that the heat-meltable resin material melts due to a rise in the temperature inside the battery. Since the gap of the separator can be closed, the internal opposition of the lithium secondary battery can be increased to make it difficult for a current to flow or to shut off the current, thereby exhibiting a shutdown function.
[0019]
Such a heat-meltable resin material may be any one as long as the melting temperature is in the range of 100 to 180 ° C., and is not particularly limited, but is a polyolefin excellent in electrolyte resistance and easily exhibiting a shutdown function. It is preferable to use a system resin. Examples of the polyolefin resin include, for example, high-density, medium-density, low-density polyethylene, ethylene-based polymers such as linear low-density polyethylene, polypropylene, and copolymers of propylene and other α-olefins (specifically, Propylene-based polymers such as propylene-butene-1 random copolymer and propylene-ethylene-butene-1 random copolymer). The heat-fusible resin material may be of one type or two or more types may be mixed.
[0020]
The heat-fusible resin material of the present invention may have any shape and is not particularly limited, and examples thereof include a pulp shape, a chopped fiber shape, and a particle shape. The `` pulp shape '' is a state in which fibrils are derived from the core, and has the feature that the denseness of the nonwoven fabric, that is, the separator, can be improved.The `` chopped fiber shape '' is a state in which fibrils are not derived, and the nonwoven fabric In other words, there is a feature that the mechanical strength of the separator can be improved. "Particulate" does not extend as long as fiber, and is spherical, rectangular, cubic, cylindrical, prismatic, rugby ball, granular, etc. , The denseness of the nonwoven fabric, ie, the separator, is improved, and the finer space can be effectively closed by melting the particulate thermofusible resin material, so that the shutdown function is improved. The separator of the present invention may include a mixture of heat-meltable resin materials having different shapes and / or constituent resins.
[0021]
When the shape of the heat-fusible resin material is a pulp shape, the freeness (CFS = Canadian Freeness Standard) should be 700 mL or less so that the separator has a dense structure and is excellent in preventing short circuit. More preferably, it is 450 mL or less. When the shape of the heat-fusible resin material is a chopped fiber shape, the fiber length (JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method)) is set so that the mechanical strength of the separator is excellent. It is preferably from 0.1 to 25 mm, more preferably from 0.25 to 20 mm. When the shape of the heat-fusible resin material is particulate, the average particle diameter is preferably 10 μm or less, more preferably 6 μm or less, so that the compactness of the separator and the shutdown function are improved. .
[0022]
In addition, this average particle diameter refers to a number average particle diameter. The number average particle diameter is obtained by enlarging and photographing the particulate heat-fusible resin material with a scanning electron microscope, measuring the particle diameters of arbitrary 500 or more particulate heat-fusible resin materials, and then measuring the particle diameter. The arithmetic mean value calculated from the particle diameter of the heat-fusible resin material. When the particulate heat-fusible resin material is not spherical, the diameter of the circumscribed circle of each particulate heat-fusible resin material is regarded as the particle diameter of each particulate heat-fusible resin material. In the case of a commercially available particulate heat-fusible resin material, if the number average particle diameter is specified in a catalog or specification, that value may be used as the average particle diameter.
[0023]
Such a heat-fusible resin material preferably occupies 10% or more, and more preferably 30% or more, of the mass of the entire separator so that the resin melts due to a rise in the temperature inside the battery and can close the voids of the separator. More preferably. On the other hand, it is preferably at most 65%, more preferably at most 50%, in view of the above-mentioned heat-resistant fiber.
[0024]
The separator of the present invention is made of a non-woven fabric containing the above-mentioned heat-resistant fiber and the heat-meltable resin material, and has excellent uniform dispersibility of the heat-resistant fiber and the heat-meltable resin material, and is unlikely to cause a short circuit. It is preferably made of a wet-laid nonwoven fabric so that the separator can have a high density.
[0025]
It is preferable that none of the constituent materials (for example, heat-resistant fiber, hot-melt resin material, etc.) of the separator of the present invention is thermally fused. Since a film is not formed due to the absence of heat fusion and the ion permeability is excellent, the electromotive action during normal use of the lithium secondary battery can be smoothly performed.
[0026]
The thickness of the separator of the present invention, that is, the nonwoven fabric, is preferably 30 μm or less, more preferably 15 to 25 μm, so that the ion permeability is excellent. The basis weight of the separator is preferably 5 to 20 g / m 2 , and the apparent density is preferably 0.1 to 1.3 g / cm 3 . This “thickness” was randomly selected and measured according to JIS C2111 5.1 (1) using an outer micrometer (0 to 25 mm) specified in JIS B 7502: 1994. The average value of points is referred to, and the “basis weight” means the basis weight obtained based on the method specified in JIS P 8124 (paper and paperboard-basis weight measurement method), and the “apparent density” is the basis weight. (G / cm 2 ) divided by the thickness (cm).
[0027]
For the separator of the present invention, a nonwoven fabric is manufactured by a conventional method, and the nonwoven fabric can be used as a separator. For example, a suitable wet nonwoven fabric can be manufactured as follows.
[0028]
First, at least a pulp-shaped heat-resistant fiber and a heat-meltable resin material are prepared. Since these materials are commercially available, they can be easily obtained.
[0029]
Then, using at least a heat-resistant fiber and a heat-fusible resin material, a conventional wet method (for example, a horizontal long net method, an inclined wire short net method, a circular net method, or a long net / circle net combination method, etc.) ) To form a wet fiber web.
[0030]
Next, the wet fiber web is dried to remove moisture, thereby obtaining a wet nonwoven fabric, that is, the separator of the present invention. The drying is preferably performed at a temperature at which the hot-melt resin material constituting the wet fiber web does not melt.
[0031]
The wet nonwoven fabric thus manufactured can be used as a separator, but it is preferable to apply pressure to the wet nonwoven fabric using a calender or the like. By applying the pressure in this manner, the thickness of the wet nonwoven fabric (that is, the separator) can be adjusted, the thickness can be reduced, and the thickness can be made uniform.
[0032]
When pressure is applied, heating may or may not be performed. However, when heating is performed, the above-described effects are easily exerted. However, if heated to such an extent that the hot-melt resin material melts, a film is formed and ion permeability deteriorates. Therefore, when heating, the resin having the lowest melting temperature among the resins constituting the wet nonwoven fabric is used. The heating is preferably performed at a temperature lower by at least 20 ° C. than the melting temperature of
[0033]
The above method is a method of manufacturing a wet nonwoven fabric using a pulp-shaped heat-resistant fiber and maintaining the shape using fibrils of the heat-resistant fiber, but when the heat-resistant fiber is in a chopped fiber shape. A non-melting fiber that can be bonded by pressure (eg, undrawn fiber) or a pulp-shaped heat-resistant fiber to form a wet fiber web; in the former case, pressure-bonded by pressure; in the latter case, A wet nonwoven fabric can be manufactured using fibrils of heat-resistant fibers.
[0034]
The lithium secondary battery of the present invention uses the separator of the present invention as described above. Therefore, since the inside of the battery does not become abnormally high temperature due to the shutdown function of the separator, there is no possibility that the electrolytic solution is ejected.
[0035]
Although the shape of the lithium secondary battery of the present invention is not particularly limited, it can be, for example, a cylindrical type, a square type, a coin type, or the like.
[0036]
The lithium secondary battery of the present invention can be composed of exactly the same materials as the conventional lithium secondary battery except that the separator of the present invention is used.
[0037]
For example, as the positive electrode material (positive electrode active material), a lithium-containing metal compound such as a lithium-containing metal oxide, sulfide or chloride can be used. As the lithium-containing metal oxide, for example, a lithium composite oxide of at least one or more metals selected from the group consisting of cobalt, manganese, nickel, chromium, iron and vanadium and lithium can be used. Examples of such a lithium composite oxide include LiCoO 2 , LiMn 2 O 4 , and LiNiO 2 .
[0038]
The positive electrode is formed by kneading the positive electrode material with a conductive agent such as acetylene black and carbon black and a binder such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) to form a positive electrode mixture. The mixture can be applied to an aluminum foil or a stainless steel lath plate as a current collector, dried and pressed, and then heat-treated under vacuum at about 50 ° C. to 250 ° C. for about 2 hours. .
[0039]
As the negative electrode (negative electrode active material), a carbon material containing lithium metal or lithium alloy, and carbon or graphite capable of occluding and releasing lithium, for example, a carbon material such as coke, natural graphite and artificial graphite, and a composite tin oxide are used. it can. The powdered carbon material can be used as a negative electrode mixture by kneading with a binder such as ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF).
[0040]
As the non-aqueous electrolyte, for example, an electrolyte is dissolved in an organic solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, γ-butyrolactone, acetonitrile, 1,2-dimethoxyethane, and tetrahydrofuran. Can be used. Examples of the electrolyte include LiPF 6 , LiBF 4 , LiClO 4 , CF 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, (C 2 F 5 SO 2 ) 2 NLi, and LiC (SO 2 CF 3 ) 3. Can be mentioned. These electrolytes may be used alone or in combination of two or more. These electrolytes are used after being dissolved in the above-mentioned organic solvent at a concentration of usually 0.1 to 3M, preferably 0.5 to 1.5M.
[0041]
The production of a lithium secondary battery using the above-mentioned components is not particularly limited. For example, a coin-type lithium secondary battery can be produced by the following method.
[0042]
First, as a negative electrode, a paste of a negative electrode mixture formed by mixing a negative electrode active material with a solution such as Pvdf-NMP (polyvinylidene fluoride-N-methylpyrrolidone) is applied on a copper foil, dried, and pressed. After molding, a heat treatment is performed to prepare a negative electrode.
[0043]
Further, as a positive electrode, a paste of a positive electrode mixture formed by mixing with a solution such as a lithium composite oxide, a conductive agent, and Pvdf-NMP is applied on an aluminum foil, dried, pressure-formed, and then heated. Process to prepare a positive electrode.
[0044]
Next, a plurality of units in which the separator of the present invention is interposed between the negative electrode and the positive electrode, and a nonaqueous electrolyte obtained by dissolving an electrolyte in an organic solvent are loaded in an outer can, and a coin-type lithium secondary battery is loaded. Can be produced.
[0045]
Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.
[0046]
【Example】
(Example 1)
As the heat-resistant fiber, a para-based wholly aromatic polyamide fiber having a pulp shape (registered trademark: Kevlar, manufactured by Dupont, carbonization temperature: 500 ° C. or more, freeness (CFS): 123 mL), and a heat-fusible resin material: High-density polyethylene pulp (registered trademark: SWP, product name: E620, manufactured by Mitsui Petrochemical Industries, melting temperature: 130 to 135 ° C, freeness (CFS): 300 mL) was prepared.
[0047]
Next, after preparing a slurry in which the para-based wholly aromatic polyamide fiber and the high-density polyethylene pulp were mixed at a mass ratio of 50:50, a slanted wire-type short net, two forward flow nets, and a Yankee dryer were provided. The slurry is supplied to a paper machine to form a combined laminated wet web formed by combining a circular web, a short net, and a circular web in this order, and then setting the combined laminated wet web to a temperature of 110 ° C. It was supplied to a dried Yankee dryer and dried to form a composite laminated dry web.
[0048]
Next, the obtained laminated dry web was pressed (linear pressure: 44 N / cm) with a pair of thermal calenders set at a temperature of 80 ° C., and had a basis weight of 15 g / m 2 , a thickness of 25 μm, and an apparent thickness. A pressed wet nonwoven fabric having a density of 0.63 g / cm 3 , that is, a separator was produced. In this separator, neither the para-based wholly aromatic polyamide fiber nor the high-density polyethylene pulp was heat-sealed.
[0049]
(Example 2)
As the heat-resistant fiber, a para-based wholly aromatic polyamide fiber having a pulp shape (registered trademark: Kevlar, manufactured by Dupont, carbonization temperature: 500 ° C. or more, freeness (CFS): 123 mL), and a heat-fusible resin material: High-density polyethylene particles (registered trademark: flow beads, product name: LE-1080, manufactured by Sumitomo Seika Co., Ltd., melting temperature: 130 to 135 ° C, average particle size: 6 µm) were prepared.
[0050]
Next, a laminated laminated dry web was formed in exactly the same manner as in Example 1 except that a slurry in which the para-based wholly aromatic polyamide fibers and the high-density polyethylene particles were mixed at a mass ratio of 50:50 was prepared. After that, pressing (linear pressure: 44 N / cm) with a pair of thermal calendars, a pressed wet nonwoven fabric having a basis weight of 15 g / m 2 , a thickness of 25 μm, and an apparent density of 0.63 g / cm 3 , A separator was manufactured. In this separator, neither the para-based wholly aromatic polyamide fiber nor the high-density polyethylene particles were heat-sealed.
[0051]
(Comparative Example 1)
A breathable paper-like sheet (Nomex paper, type 411, manufactured by DuPont) having a structure in which synthetic pulp, which is a polymer of a wholly aromatic polyamide, is dispersed in gaps between aramid fibers, which are a polymer of a wholly aromatic polyamide. , Nominal thickness: 0.127 mm, basis weight: 39 g / m 2 , and average density when dried: 0.28 g / cm 3 ) were used as the separator.
[0052]
(Comparative Example 2)
Immediately after forming a polypropylene fiber web having a fiber diameter of 4 to 8 μm on a conveyor by a melt blow method, the fiber is heated to 90 ° C. and pressure-bonded with a re-ant press to have a basis weight of 35 g / m 2 . A pressure-bonded fiber web having a thickness of 65 μm was formed.
[0053]
Next, the pressure-bonded fiber web is impregnated with an emulsion of low-density polyethylene (melting point: 110 ° C.) and dried to form an adhesive nonwoven fabric having 7 g / m 2 of the low-density polyethylene adhered thereto at a solid content. A separator was used.
[0054]
(Comparative Example 3)
Except that 100% of the para-based wholly aromatic polyamide fiber used in Example 1 was used, the formation of a laminated dry web and pressing with a pair of heat calenders were performed in exactly the same manner as in Example 1. A pressed wet nonwoven fabric having a basis weight of 20 g / m 2 , a thickness of 25 μm, and an apparent density of 0.8 g / cm 3 , that is, a separator was produced. In this separator, the para-based wholly aromatic polyamide fiber was not heat-sealed.
[0055]
(Production of lithium secondary battery)
First, a paste in which a mesophase microsphere was graphitized and a Pvdf-NMP (polyvinylidene fluoride-N-methylpyrrolidone: 13% by weight) solution was mixed at a solid content mass ratio of 90:10 on a copper foil. After coating, drying, and pressure molding, a heat treatment was performed to prepare a negative electrode.
[0056]
Further, as a positive electrode, a paste in which a LiCoO 2 : acetylene black: Pvdf-NMP solution (12% by weight) was mixed at a solid content mass ratio of 85: 5: 10 was applied onto an aluminum foil, dried, and pressed. After heating, a positive electrode was prepared.
[0057]
Next, 1 mol / L of LiPF 6 was dissolved in a solvent in which ethylene carbonate / diethyl carbonate was mixed at a volume ratio of 1: 1 using the separators of Examples 1 to 2 and Comparative Examples 1 to 3 as separators, respectively. A non-aqueous electrolyte is prepared, a plurality of units having the separator interposed between a negative electrode and a positive electrode, and the non-aqueous electrolyte are loaded in an outer can, and a coin-type lithium secondary battery (diameter: 20 mm, thickness: 3.2 mm).
[0058]
(Measurement of internal resistance)
The internal resistance (initial resistance value) at a temperature of 20 ° C. of the coin-type lithium secondary battery manufactured by the above method was measured at 1 kHz.
[0059]
Next, the coin-type lithium secondary battery was placed on a hot plate installed in an explosion-proof dryer, and the temperature was increased from 20 ° C to 200 ° C at a rate of 5 ° C / min. In this process, the internal resistance at temperatures of 130 ° C. and 200 ° C. was measured. These results were as shown in Table 1.
[0060]
[Table 1]
As is clear from Table 1, in the separators of Examples 1 and 2 of the present invention, since the internal resistance at 130 ° C. was increased, it could be inferred that the shutdown function was working. . This was thought to be due to the melting of the hot-melt resin material constituting the separator.
[0062]
In addition, the separators of Examples 1 and 2 of the present invention were able to measure the internal resistance without exposing the battery to heat even when exposed to a high temperature of 200 ° C., without squirting out the electrolyte and causing damage. Therefore, it could be inferred that the separator did not melt or shrink.
[0063]
【The invention's effect】
Since the lithium secondary battery separator of the present invention does not melt and form a large hole or shrink even if the temperature is increased to a high temperature exceeding 180 ° C., the electrode Does not cause short circuit due to exposure of In addition, since a shutdown function can be exhibited, it can be applied to various lithium secondary batteries.
[0064]
The lithium secondary battery of the present invention does not have a possibility of ejecting the electrolytic solution.
Claims (6)
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| JP2003000753A JP4350953B2 (en) | 2003-01-07 | 2003-01-07 | Lithium secondary battery separator and lithium secondary battery |
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| JP2003000753A JP4350953B2 (en) | 2003-01-07 | 2003-01-07 | Lithium secondary battery separator and lithium secondary battery |
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| JP2004214066A true JP2004214066A (en) | 2004-07-29 |
| JP4350953B2 JP4350953B2 (en) | 2009-10-28 |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006059717A (en) * | 2004-08-20 | 2006-03-02 | Nissan Motor Co Ltd | Separator for battery |
| DE102009028145A1 (en) | 2009-07-31 | 2011-02-03 | Evonik Degussa Gmbh | Ceramic membranes with polyaramid fiber-containing support materials and process for making these membranes |
| KR20120101341A (en) | 2009-10-15 | 2012-09-13 | 미쓰비시 세이시 가부시키가이샤 | Substrate for lithium secondary battery, and separator for lithium secondary battery |
| JP2015180856A (en) * | 2014-03-06 | 2015-10-15 | 株式会社神戸製鋼所 | Corrosion monitoring sensor, corrosion depth calculation system, and metal corrosion speed calculation system |
| US9614249B2 (en) | 2013-10-29 | 2017-04-04 | Panasonic Corporation | Separator for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery |
| KR101796283B1 (en) | 2013-11-05 | 2017-11-10 | 주식회사 엘지화학 | Composite separator based non-woven fabric and a method of making the same |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP7148198B2 (en) | 2015-03-05 | 2022-10-05 | 日本電気株式会社 | SECONDARY BATTERY SEPARATOR AND SECONDARY BATTERY HAVING THE SAME |
-
2003
- 2003-01-07 JP JP2003000753A patent/JP4350953B2/en not_active Expired - Fee Related
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2006059717A (en) * | 2004-08-20 | 2006-03-02 | Nissan Motor Co Ltd | Separator for battery |
| DE102009028145A1 (en) | 2009-07-31 | 2011-02-03 | Evonik Degussa Gmbh | Ceramic membranes with polyaramid fiber-containing support materials and process for making these membranes |
| KR20120101341A (en) | 2009-10-15 | 2012-09-13 | 미쓰비시 세이시 가부시키가이샤 | Substrate for lithium secondary battery, and separator for lithium secondary battery |
| US9614249B2 (en) | 2013-10-29 | 2017-04-04 | Panasonic Corporation | Separator for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery |
| KR101796283B1 (en) | 2013-11-05 | 2017-11-10 | 주식회사 엘지화학 | Composite separator based non-woven fabric and a method of making the same |
| JP2015180856A (en) * | 2014-03-06 | 2015-10-15 | 株式会社神戸製鋼所 | Corrosion monitoring sensor, corrosion depth calculation system, and metal corrosion speed calculation system |
Also Published As
| Publication number | Publication date |
|---|---|
| JP4350953B2 (en) | 2009-10-28 |
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