JP2010123465A - Separator for battery and lithium secondary battery - Google Patents
Separator for battery and lithium secondary battery Download PDFInfo
- Publication number
- JP2010123465A JP2010123465A JP2008297465A JP2008297465A JP2010123465A JP 2010123465 A JP2010123465 A JP 2010123465A JP 2008297465 A JP2008297465 A JP 2008297465A JP 2008297465 A JP2008297465 A JP 2008297465A JP 2010123465 A JP2010123465 A JP 2010123465A
- Authority
- JP
- Japan
- Prior art keywords
- porous membrane
- separator
- battery
- polyolefin
- melting point
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 43
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 40
- 239000012528 membrane Substances 0.000 claims abstract description 101
- 229920000098 polyolefin Polymers 0.000 claims abstract description 63
- 239000011256 inorganic filler Substances 0.000 claims abstract description 57
- 229910003475 inorganic filler Inorganic materials 0.000 claims abstract description 57
- 238000002844 melting Methods 0.000 claims abstract description 57
- 230000008018 melting Effects 0.000 claims abstract description 57
- 239000000203 mixture Substances 0.000 claims abstract description 25
- 239000002245 particle Substances 0.000 claims abstract description 19
- 239000004698 Polyethylene Substances 0.000 claims description 18
- -1 polyethylene Polymers 0.000 claims description 18
- 229920000573 polyethylene Polymers 0.000 claims description 18
- 239000004743 Polypropylene Substances 0.000 claims description 14
- 229920001155 polypropylene Polymers 0.000 claims description 14
- 229910001593 boehmite Inorganic materials 0.000 claims description 10
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 claims description 10
- 239000005486 organic electrolyte Substances 0.000 claims description 10
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 8
- 239000011149 active material Substances 0.000 claims description 8
- 229910001416 lithium ion Inorganic materials 0.000 claims description 7
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 6
- 239000000377 silicon dioxide Substances 0.000 claims description 4
- 230000008602 contraction Effects 0.000 abstract description 5
- 239000002075 main ingredient Substances 0.000 abstract 1
- 239000002002 slurry Substances 0.000 description 30
- 238000000034 method Methods 0.000 description 20
- 239000011230 binding agent Substances 0.000 description 19
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- 230000000052 comparative effect Effects 0.000 description 12
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- 230000001965 increasing effect Effects 0.000 description 10
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- 239000002184 metal Substances 0.000 description 8
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 6
- 239000002033 PVDF binder Substances 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 6
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 6
- 239000011888 foil Substances 0.000 description 6
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
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- 229920000178 Acrylic resin Polymers 0.000 description 5
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 5
- 238000007600 charging Methods 0.000 description 5
- 239000011248 coating agent Substances 0.000 description 5
- 238000000576 coating method Methods 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 229910003002 lithium salt Inorganic materials 0.000 description 5
- 159000000002 lithium salts Chemical class 0.000 description 5
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- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 4
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- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 3
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 3
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- DNIAPMSPPWPWGF-UHFFFAOYSA-N Propylene glycol Chemical compound CC(O)CO DNIAPMSPPWPWGF-UHFFFAOYSA-N 0.000 description 3
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- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 2
- 229910013870 LiPF 6 Inorganic materials 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 2
- 229910010413 TiO 2 Inorganic materials 0.000 description 2
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- OCKPCBLVNKHBMX-UHFFFAOYSA-N butylbenzene Chemical compound CCCCC1=CC=CC=C1 OCKPCBLVNKHBMX-UHFFFAOYSA-N 0.000 description 2
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- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
- 229920006244 ethylene-ethyl acrylate Polymers 0.000 description 2
- 239000000499 gel Substances 0.000 description 2
- MRNHPUHPBOKKQT-UHFFFAOYSA-N indium;tin;hydrate Chemical compound O.[In].[Sn] MRNHPUHPBOKKQT-UHFFFAOYSA-N 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
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- 239000000454 talc Substances 0.000 description 2
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- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 2
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- WNXJIVFYUVYPPR-UHFFFAOYSA-N 1,3-dioxolane Chemical compound C1COCO1 WNXJIVFYUVYPPR-UHFFFAOYSA-N 0.000 description 1
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- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 1
- 239000011029 spinel Substances 0.000 description 1
- 229910052596 spinel Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical class [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 238000004381 surface treatment Methods 0.000 description 1
- 239000004094 surface-active agent Substances 0.000 description 1
- ZUHZGEOKBKGPSW-UHFFFAOYSA-N tetraglyme Chemical compound COCCOCCOCCOCCOC ZUHZGEOKBKGPSW-UHFFFAOYSA-N 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
- YFNKIDBQEZZDLK-UHFFFAOYSA-N triglyme Chemical compound COCCOCCOCCOC YFNKIDBQEZZDLK-UHFFFAOYSA-N 0.000 description 1
- 239000000230 xanthan gum Substances 0.000 description 1
- 229920001285 xanthan gum Polymers 0.000 description 1
- 235000010493 xanthan gum Nutrition 0.000 description 1
- 229940082509 xanthan gum Drugs 0.000 description 1
- 239000010457 zeolite 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
本発明は、耐熱性に優れた電池用セパレータ、およびこれを用いてなり、信頼性に優れた安全なリチウム二次電池に関するものである。 The present invention relates to a battery separator excellent in heat resistance and a safe lithium secondary battery excellent in reliability using the same.
非水電解質電池の一種であるリチウム二次電池は、エネルギー密度が高いという特徴から、携帯電話やノート型パーソナルコンピューターなどの携帯機器の電源として広く用いられている。例えば、リチウム二次電池では、携帯機器の高性能化に伴って高容量化が更に進む傾向にあり、安全性の確保が重要となっている。 A lithium secondary battery, which is a type of nonaqueous electrolyte battery, is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density. For example, lithium secondary batteries tend to have higher capacities as mobile devices become more sophisticated, and ensuring safety is important.
現行のリチウム二次電池では、正極と負極の間に介在させるセパレータとして、例えば厚みが２０〜３０μｍ程度のポリオレフィン系の多孔性フィルムが使用されている。また、セパレータの素材としては、電池の熱暴走温度以下でセパレータの構成樹脂を溶融させて空孔を閉塞させ、これにより電池の内部抵抗を上昇させて短絡の際などに電池の安全性を向上させる所謂シャットダウン効果を確保するため、融点の低いポリエチレンが適用されることがある。 In current lithium secondary batteries, a polyolefin-based porous film having a thickness of, for example, about 20 to 30 μm is used as a separator interposed between a positive electrode and a negative electrode. In addition, as separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to ensure the so-called shutdown effect, polyethylene having a low melting point may be applied.
ところで、こうしたセパレータとしては、例えば、多孔化と強度向上のために一軸延伸または二軸延伸したフィルムが用いられている。このようなセパレータは、単独で存在する膜として供給されるため、作業性などの点で一定の強度が要求され、これを前記延伸によって確保している。しかし、このような延伸フィルムでは結晶化度が増大しており、シャットダウン温度も、電池の熱暴走温度に近い温度にまで高まっているため、電池の安全性確保のためのマージンが十分とは言い難い。 By the way, as such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used for increasing the porosity and improving the strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is secured by the stretching. However, with such a stretched film, the degree of crystallinity has increased, and the shutdown temperature has increased to a temperature close to the thermal runaway temperature of the battery. Therefore, it can be said that the margin for ensuring the safety of the battery is sufficient. hard.
また、前記延伸によってフィルムにはひずみが生じており、これが高温に曝されると、残留応力によって収縮が起こるという問題がある。収縮温度は、融点、すなわちシャットダウン温度と非常に近いところに存在する。 In addition, the film is distorted by the stretching, and there is a problem that when it is exposed to a high temperature, shrinkage occurs due to residual stress. The shrinkage temperature is very close to the melting point, ie the shutdown temperature.
前記のような高温時の収縮を抑制するために、樹脂多孔質膜の表面に、耐熱性微粒子を含有する耐熱多孔質層を形成してセパレータを構成することが提案されている（例えば、特許文献１）。 In order to suppress the above-described shrinkage at high temperatures, it has been proposed to form a separator by forming a heat-resistant porous layer containing heat-resistant fine particles on the surface of the resin porous membrane (for example, patents) Reference 1).
特許文献１に開示の技術によれば、異常過熱した際にもセパレータの収縮を抑制できるため、短絡し難く、熱暴走が生じ難い安全性に優れた電池を提供することができる。 According to the technique disclosed in Patent Document 1, since the shrinkage of the separator can be suppressed even when abnormally overheated, it is possible to provide a battery that is less likely to be short-circuited and is less likely to cause thermal runaway and excellent in safety.
ところで、セパレータによって確保するシャットダウン温度は、電池の安全性のマージンを確保するため、正極活物質の熱暴走温度よりもなるべく低温とすることが望ましいが、例えば特許文献１に記載のセパレータにおいて、ポリエチレンを主体として構成された樹脂多孔質膜を用いた場合、シャットダウン温度がポリエチレンの融点に近い１２０〜１４０℃近辺となる。なお、外部短絡が生じた場合のように、シャットダウンによって樹脂多孔質膜内の空孔を閉塞して直ちに短絡電流を抑え、電池の温度を低下させる必要がある条件下においては、シャットダウン温度は低い方が、電池の安全性確保の観点からは好ましい。 By the way, the shutdown temperature secured by the separator is preferably as low as possible than the thermal runaway temperature of the positive electrode active material in order to secure a safety margin of the battery. For example, in the separator described in Patent Document 1, polyethylene is used. When the resin porous membrane constituted mainly is used, the shutdown temperature is in the vicinity of 120 to 140 ° C. close to the melting point of polyethylene. Note that the shutdown temperature is low under conditions where it is necessary to reduce the battery temperature by immediately closing the vacancies in the porous resin membrane by shutting down, as in the case of an external short circuit, and suppressing the short circuit current. This is preferable from the viewpoint of ensuring the safety of the battery.
一方、シャットダウン温度、すなわち樹脂多孔質膜を構成するポリオレフィンの融点以上の温度環境下で電池が長時間保持されるような場合においては、溶融したポリオレフィンが、電極と耐熱多孔質層との間で被膜を形成し、樹脂多孔質膜の孔を閉塞したままシャットダウン状態を維持することが重要となる。 On the other hand, in the case where the battery is kept for a long time under the shutdown temperature, that is, the temperature environment equal to or higher than the melting point of the polyolefin constituting the resin porous membrane, the molten polyolefin is interposed between the electrode and the heat-resistant porous layer. It is important to form a film and maintain the shutdown state while closing the pores of the resin porous membrane.
しかし、溶融したポリオレフィンは流動性を有しているため、電極内の空孔や耐熱多孔質層内の空孔へと散逸する。特に、充電状態の電極と非水電解液との発熱反応などで、電池の温度がオーバーシュートした場合には、セパレータに係るポリオレフィンの流動性が更に増加するため、樹脂多孔質膜において、孔を十分に閉塞できない部分が生じる虞がある。 However, since the melted polyolefin has fluidity, it is dissipated into holes in the electrode and holes in the heat-resistant porous layer. In particular, when the temperature of the battery overshoots due to an exothermic reaction between the charged electrode and the nonaqueous electrolytic solution, the fluidity of the polyolefin related to the separator further increases. There is a possibility that a portion that cannot be sufficiently closed may be generated.
このように、シャットダウン状態が良好に維持できないまま、電池が高温環境下に長時間放置されるなどし、電池の一部で微短絡が発生したりすると、短絡電流が多く流れ、電池の温度上昇が激しくなって熱暴走に陥りやすくなる虞がある。このような点で、特許文献１に開示の技術は、未だ改善の余地を残している。 In this way, if the battery is left in a high temperature environment for a long time without being able to maintain a good shutdown state, or if a short circuit occurs in a part of the battery, a large amount of short circuit current flows and the battery temperature rises. May become violent and become prone to thermal runaway. In this respect, the technique disclosed in Patent Document 1 still leaves room for improvement.
本発明は前記事情に鑑みてなされたものであり、その目的は、電池にシャットダウン機能を付与でき、かつ高温でもシャットダウン状態を維持可能な電池用セパレータと、該電池用セパレータを用いたリチウム二次電池とを提供することにある。 The present invention has been made in view of the above circumstances, and an object thereof is to provide a battery separator capable of providing a shutdown function and maintain a shutdown state even at a high temperature, and a lithium secondary using the battery separator. It is to provide a battery.
前記目的を達成し得た本発明の電池用セパレータ（以下、単に「セパレータ」という場合がある。）は、無機フィラーを少なくとも含有する多孔質膜（Ａ）と、ポリオレフィンを主体とする多孔質膜（Ｂ）とを有し、かつ前記多孔質膜（Ａ）と前記多孔質膜（Ｂ）とが一体化している電池用セパレータであって、前記多孔質膜（Ａ）の含有する前記無機フィラーは、板状の粒子が主体であり、前記多孔質膜（Ｂ）における前記ポリオレフィンが、融点が１５０℃未満のポリオレフィンと、融点が１５０℃以上のポリオレフィンとの混合物であり、前記多孔質膜（Ｂ）の含有する融点が１５０℃未満のポリオレフィンの融点以上であって、融点が１５０℃以上のポリオレフィンの融点以下の温度における熱収縮率が、５％以下であることを特徴とするものである。 The battery separator of the present invention that can achieve the above-mentioned object (hereinafter sometimes simply referred to as “separator”) includes a porous film (A) containing at least an inorganic filler and a porous film mainly composed of polyolefin. (B), and a separator for a battery in which the porous membrane (A) and the porous membrane (B) are integrated, and the inorganic filler contained in the porous membrane (A) Is mainly composed of plate-like particles, and the polyolefin in the porous membrane (B) is a mixture of a polyolefin having a melting point of less than 150 ° C. and a polyolefin having a melting point of 150 ° C. or more. The melting point contained in B) is not less than the melting point of the polyolefin having a temperature of less than 150 ° C., and the thermal shrinkage at a temperature not higher than the melting point of the polyolefin having a melting point of not less than 150 ° C. is 5% or less. It is intended to.
また、本発明のリチウム二次電池は、Ｌｉイオンを吸蔵放出可能な活物質を含有する正極と、Ｌｉイオンを吸蔵放出可能な活物質を含有する負極と、有機電解液と、セパレータとを備えており、前記セパレータが本発明の電池用セパレータであることを特徴とするものである。 The lithium secondary battery of the present invention includes a positive electrode containing an active material capable of occluding and releasing Li ions, a negative electrode containing an active material capable of occluding and releasing Li ions, an organic electrolyte, and a separator. The separator is a battery separator of the present invention.
本発明によれば、電池にシャットダウン機能を付与でき、かつ高温でもシャットダウン状態が維持可能な電池用セパレータと、該電池用セパレータを用いたリチウム二次電池とを提供することができる。本発明のリチウム二次電池は、優れた信頼性および安全性を有している。 ADVANTAGE OF THE INVENTION According to this invention, the battery separator which can provide a shutdown function to a battery and can maintain a shutdown state also at high temperature, and the lithium secondary battery using this battery separator can be provided. The lithium secondary battery of the present invention has excellent reliability and safety.
本発明の電池用セパレータは、ポリオレフィンを主体とする多孔質膜（Ｂ）を基材とし、前記基材の表面に耐熱性を有する多孔質膜（Ａ）を形成して構成する。 The battery separator of the present invention is constituted by using a porous membrane (B) mainly composed of polyolefin as a base material and forming a heat-resistant porous membrane (A) on the surface of the base material.
多孔質膜（Ａ）は、無機フィラーを少なくとも含有しており、前記無機フィラーは、板状の粒子を主体とする。板状の無機フィラーは、本発明のセパレータにおいて、その耐熱性を高め、セパレータの高温での寸法安定性（形状安定性）を向上させたり、リチウムデンドライトに起因する微小短絡の発生を抑制する作用を有するものである。なお、板状の無機フィラーは、例えば球状の無機フィラーに比べて、基材となる多孔質膜（Ｂ）との接触面積が大きくなる。そのため、板状の無機フィラーを用いて多孔質膜（Ａ）を構成することで、セパレータの収縮を抑制する作用がより向上する。特に、シャットダウン温度近辺で、多孔質膜（Ｂ）に係る融点が１５０℃未満のポリオレフィンが軟化した際に、接触面積の大きな板状の無機フィラーの作用によって、セパレータの収縮が良好に抑制される。 The porous membrane (A) contains at least an inorganic filler, and the inorganic filler is mainly composed of plate-like particles. In the separator of the present invention, the plate-like inorganic filler increases the heat resistance, improves the dimensional stability (shape stability) of the separator at a high temperature, and suppresses the occurrence of a micro short circuit caused by lithium dendrite. It is what has. Note that the plate-like inorganic filler has a larger contact area with the porous membrane (B) serving as the base material than, for example, a spherical inorganic filler. Therefore, the effect | action which suppresses shrinkage | contraction of a separator improves more by comprising a porous membrane (A) using a plate-shaped inorganic filler. In particular, when the polyolefin having a melting point of less than 150 ° C. is softened near the shutdown temperature, the shrinkage of the separator is satisfactorily suppressed by the action of the plate-like inorganic filler having a large contact area. .
板状の無機フィラーは、電気絶縁性を有しており、電気化学的に安定で、更に後述する有機電解液や、多孔質膜（Ａ）形成用のスラリー（溶媒を含む組成物）に用いる溶媒に対して安定であり、高温状態で有機電解液に溶解しないものであれば、特に制限はない。 The plate-like inorganic filler has electrical insulating properties, is electrochemically stable, and is used for an organic electrolyte solution described later and a slurry for forming a porous film (A) (composition containing a solvent). There is no particular limitation as long as it is stable to a solvent and does not dissolve in an organic electrolyte at a high temperature.
なお、本明細書でいう「有機電解液に対して安定な無機フィラー」とは、有機電解液（電池の電解液として使用される有機電解液）中で変形および化学的組成変化の起こらない無機フィラーを意味している。また、本明細書でいう「高温状態」とは、具体的には１５０℃以上の温度であり、無機フィラーは、このような温度の電解液中で変形および化学的組成変化の起こらない安定な粒子であればよい。更に、本明細書でいう「電気化学的に安定な」とは、電池の充放電の際に化学変化が生じないことを意味している。 As used herein, “an inorganic filler that is stable with respect to an organic electrolyte” refers to an inorganic material that does not undergo deformation or chemical composition change in an organic electrolyte (an organic electrolyte used as a battery electrolyte). Means filler. In addition, the “high temperature state” in the present specification is specifically a temperature of 150 ° C. or higher, and the inorganic filler is stable without causing deformation and chemical composition change in the electrolytic solution at such temperature. Any particles may be used. Further, “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the battery.
板状の無機フィラーの具体例としては、例えば、酸化鉄、Ａｌ２Ｏ３（アルミナ）、ＳｉＯ２（シリカ）、ＴｉＯ２、ＢａＴｉＯ３、ＺｒＯ２などの酸化物微粒子；窒化アルミニウム、窒化ケイ素などの窒化物微粒子；フッ化カルシウム、フッ化バリウム、硫酸バリウムなどの難溶性のイオン結晶微粒子；シリコン、ダイヤモンドなどの共有結合性結晶微粒子；タルク、モンモリロナイトなどの粘土微粒子；ベーマイト、ゼオライト、アパタイト、カオリン、ムライト、スピネル、オリビン、セリサイト、ベントナイトなどの鉱物資源由来物質またはそれらの人造物；などが挙げられる。また、金属微粒子；ＳｎＯ２、スズ−インジウム酸化物（ＩＴＯ）などの酸化物微粒子；カーボンブラック、グラファイトなどの炭素質微粒子；などの導電性微粒子の表面を、電気絶縁性を有する材料（例えば、前記の無機フィラーを構成する絶縁性の材料など）で表面処理することで、電気絶縁性を持たせた微粒子であってもよい。これらの中でも、アルミナ、シリカおよびベーマイトよりなる群から選択される少なくとも１種の粒子であることが好ましい。板状の無機フィラーには、これらを１種単独で用いてもよく、２種以上を併用してもよい。 Specific examples of the plate-like inorganic filler include fine oxide particles such as iron oxide, Al 2 O 3 (alumina), SiO 2 (silica), TiO 2 , BaTiO 3 , ZrO 2 ; aluminum nitride, silicon nitride, etc. Nitride fine particles; poorly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; boehmite, zeolite, apatite and kaolin , Mullite, spinel, olivine, sericite, bentonite and other mineral resource-derived substances or artificial products thereof. Further, the surface of conductive fine particles such as metal fine particles; oxide fine particles such as SnO 2 and tin-indium oxide (ITO); carbon fine particles such as carbon black and graphite; Fine particles imparted with electrical insulation by surface treatment with an insulating material constituting the inorganic filler) may be used. Among these, at least one particle selected from the group consisting of alumina, silica and boehmite is preferable. These may be used alone or in combination of two or more for the plate-like inorganic filler.
板状の無機フィラーの形態としては、例えば、アスペクト比（板状粒子中の最大長さと板状粒子の厚みの比）が、好ましくは５以上、より好ましくは１０以上であって、好ましくは１００以下、より好ましくは５０以下である。また、粒子の平板面の長軸方向長さと短軸方向長さの比の平均値は、好ましくは０．３以上、より好ましくは０．５以上である（１、すなわち、長軸方向長さと短軸方向長さとが同じであってもよい）。板状の無機フィラーが、前記のようなアスペクト比や平板面の長軸方向長さと短軸方向長さの比の平均値を有する場合には、前記の短絡防止作用がより有効に発揮される。 As the form of the plate-like inorganic filler, for example, the aspect ratio (ratio of the maximum length in the plate-like particles to the thickness of the plate-like particles) is preferably 5 or more, more preferably 10 or more, and preferably 100. Below, more preferably 50 or less. Moreover, the average value of the ratio of the major axis direction length to the minor axis direction length of the tabular surface of the grain is preferably 0.3 or more, more preferably 0.5 or more (ie, the major axis direction length and The length in the minor axis direction may be the same). When the plate-like inorganic filler has an average value of the aspect ratio and the ratio of the length in the long axis direction to the length in the short axis direction of the flat plate surface as described above, the short-circuit preventing effect is more effectively exhibited. .
板状の無機フィラーにおける前記のアスペクト比や平板面の長軸方向長さと短軸方向長さの比の平均値は、例えば、走査型電子顕微鏡（ＳＥＭ）により撮影した画像を画像解析することにより求めることができる。 The average value of the aspect ratio of the plate-like inorganic filler and the ratio of the long-axis direction length to the short-axis direction length of the flat plate surface is obtained, for example, by analyzing an image taken with a scanning electron microscope (SEM). Can be sought.
なお、板状の無機フィラーには、例えば各種市販品を用いることができ、具体的には、旭硝子エスアイテック社製「サンラブリー（商品名）」（ＳｉＯ２）、石原産業社製「ＮＳＴ−Ｂ１（商品名）」の粉砕品（ＴｉＯ２）、堺化学工業社製の板状硫酸バリウム「Ｈシリーズ（商品名）」、「ＨＬシリーズ（商品名）」、林化成社製「ミクロンホワイト（商品名）」（タルク）、林化成社製「ベンゲル（商品名）」（ベントナイト）、河合石灰社製「ＢＭＭ（商品名）」や「ＢＭＴ（商品名）」（ベーマイト）、河合石灰社製「セラシュールＢＭＴ−Ｂ（商品名）」［アルミナ（Ａｌ２Ｏ３）］、キンセイマテック社製「セラフ（商品名）」（アルミナ）、斐川鉱業社製「斐川マイカ Ｚ−２０（商品名）」（セリサイト）などが入手可能である。この他、ＳｉＯ２、Ａｌ２Ｏ３、ＺｒＯ、ＣｅＯ２については、特開２００３−２０６４７５号公報に開示の方法により作製することができる。 As the plate-like inorganic filler, for example, various commercially available products can be used. Specifically, “Sun Lovely (trade name)” (SiO 2 ) manufactured by Asahi Glass S-Tech Co., Ltd., “NST-” manufactured by Ishihara Sangyo Co., Ltd. B1 (trade name) crushed product (TiO 2 ), plate barium sulfate “H series (trade name)”, “HL series (trade name)” manufactured by Sakai Chemical Industry Co., Ltd., “Micron White ( (Trade name) ”(talc),“ Bengell (trade name) ”(bentonite) manufactured by Hayashi Kasei Co., Ltd.“ BMM (trade name) ”or“ BMT (trade name) ”(boehmite) manufactured by Kawai Lime Co., Ltd. “Cerasure BMT-B (trade name)” [Alumina (Al 2 O 3 )], “Seraph (trade name)” (alumina) manufactured by Kinsei Matec Co., Ltd., “Yodogawa Mica Z-20 (trade name) manufactured by Yodogawa Mining Co., Ltd. (Serisite) etc. are available It is. In addition, SiO 2 , Al 2 O 3 , ZrO, and CeO 2 can be produced by the method disclosed in Japanese Patent Laid-Open No. 2003-206475.
セパレータ中において、板状の無機フィラーを、その平板面がセパレータの面にほぼ平行となるように配向させることが好ましく、このような構成とすることで、セパレータの収縮をより良好に抑制できるようになる。これは、板状の無機フィラーを前記のように配向させることで、板状の無機フィラー同士が平板面の一部で重なるように配置されることから、無機フィラー同士の接着力が大きくなって、より大きな収縮応力に耐え得るようになると考えられ、これにより、セパレータの収縮がより良好に抑制されるものと推定される。 In the separator, it is preferable to orient the plate-like inorganic filler so that the flat plate surface thereof is substantially parallel to the surface of the separator. By adopting such a configuration, it is possible to better suppress the shrinkage of the separator. become. This is because the plate-like inorganic filler is oriented as described above, so that the plate-like inorganic fillers are arranged so as to overlap each other on a part of the flat plate surface, so that the adhesive force between the inorganic fillers increases. It is estimated that the separator can withstand a larger shrinkage stress, and thus the shrinkage of the separator is better suppressed.
多孔質膜（Ａ）の含有する無機フィラーは、前記の板状の無機フィラーを主体とし、板状の無機フィラーのみを含有していてもよいが、板状以外の形状、例えば、球状、粒子状、針状などの種々の形状の無機フィラーを、板状の無機フィラーと共に含有していてもよい。板状以外の形状の無機フィラーとしては、板状の無機フィラーの具体例として先に例示した各種微粒子と同じ材質の微粒子を用いることができる。 The inorganic filler contained in the porous membrane (A) is mainly composed of the plate-like inorganic filler, and may contain only the plate-like inorganic filler. Various shape fillers such as needles and needles may be contained together with the plate-like inorganic filler. As the inorganic filler having a shape other than the plate shape, fine particles of the same material as the various fine particles exemplified above as a specific example of the plate-like inorganic filler can be used.
なお、多孔質膜（Ａ）が、板状の無機フィラーと、板状以外の形状の無機フィラーとを含有する場合、主体となる板状の無機フィラーの比率は、多孔質層（Ａ）の含有する無機フィラーの総量を１００質量％としたとき、５０質量％以上であり、９０質量％以上であることが好ましい。 In addition, when the porous film (A) contains a plate-like inorganic filler and an inorganic filler having a shape other than a plate-like shape, the ratio of the plate-like inorganic filler as a main component is that of the porous layer (A). When the total amount of the inorganic filler to be contained is 100% by mass, it is 50% by mass or more, and preferably 90% by mass or more.
板状の無機フィラー、および板状以外の形状の無機フィラーの平均粒径は、例えば、０．０１μｍ以上であることが好ましく、０．１μｍ以上であることがより好ましく、また、１５μｍ以下であることが好ましく、５μｍ以下であることがより好ましい。なお、本明細書でいう無機フィラーの平均粒径は、例えば、レーザー散乱粒度分布計（例えば、ＨＯＲＩＢＡ社製「ＬＡ−９２０」）を用い、無機フィラーが溶解したり膨潤したりしない媒体に、無機フィラーを分散させて測定した数平均粒子径として規定することができる。 The average particle diameter of the plate-like inorganic filler and the non-plate-like inorganic filler is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and 15 μm or less. The thickness is preferably 5 μm or less. In addition, the average particle diameter of the inorganic filler referred to in the present specification is, for example, a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA), and the medium in which the inorganic filler does not dissolve or swell, It can be defined as the number average particle size measured by dispersing the inorganic filler.
多孔質膜（Ａ）は、無機フィラー同士を接着したり、多孔質膜（Ａ）と多孔質膜（Ｂ）とを接着したりするために、バインダを含有していることが好ましい。バインダとしては、無機フィラー同士や、多孔質膜（Ａ）と多孔質膜（Ｂ）とを良好に接着でき、電池内部で電気化学的に安定であり、電池の有する有機電解液に対して安定であるものであればいずれでもよいが、例えば、エチレン−酢酸ビニル共重合体（ＥＶＡ、酢酸ビニル由来の構造単位が２０〜３５モル％のもの）、エチレン−エチルアクリレート共重合体などのエチレン−アクリル酸共重合体、フッ素系ゴム、スチレン−ブタジエンゴム（ＳＢＲ）、ポリビニルアルコール（ＰＶＡ）、ポリビニルブチラール（ＰＶＢ）、ポリビニルピロリドン（ＰＶＰ）、ポリＮ−ビニルアセトアミド、架橋アクリル樹脂、ポリウレタン、エポキシ樹脂などが用いられる。これらのバインダは、１種単独で使用してもよく、２種以上を併用してもよい。 The porous membrane (A) preferably contains a binder in order to adhere inorganic fillers to each other or to adhere the porous membrane (A) and the porous membrane (B). As a binder, inorganic fillers, porous membrane (A) and porous membrane (B) can be bonded well, are electrochemically stable inside the battery, and are stable against the organic electrolyte contained in the battery. Any ethylene-vinyl acetate copolymer (EVA, having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-ethyl acrylate copolymer, and the like may be used. Acrylic acid copolymer, fluorinated rubber, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), poly N-vinylacetamide, cross-linked acrylic resin, polyurethane, epoxy resin Etc. are used. These binders may be used individually by 1 type, and may use 2 or more types together.
前記例示のバインダの中でも、１５０℃以上の耐熱性を有する耐熱樹脂が好ましく、特に、エチレン−アクリル酸共重合体、フッ素系ゴム、ＳＢＲなどの柔軟性の高い材料がより好ましい。これらの具体例としては、三井デュポンポリケミカル社製の「エバフレックスシリーズ（ＥＶＡ、商品名）」、日本ユニカー社製のＥＶＡ、三井デュポンポリケミカル社製の「エバフレックス−ＥＥＡシリーズ（エチレン−アクリル酸共重合体、商品名）」、日本ユニカー社製のＥＥＡ、ダイキン工業社製の「ダイエルラテックスシリーズ（フッ素ゴム、商品名）」、ＪＳＲ社製の「ＴＲＤ−２００１（ＳＢＲ、商品名）」、日本ゼオン社製の「ＥＭ−４００Ｂ（ＳＢＲ、商品名）」などが挙げられる。また、アクリル酸ブチルを主成分とし、これを架橋した構造を有する低ガラス転移温度の架橋アクリル樹脂（自己架橋型アクリル樹脂）も好ましい。 Among the binders exemplified above, a heat-resistant resin having a heat resistance of 150 ° C. or higher is preferable, and in particular, a highly flexible material such as ethylene-acrylic acid copolymer, fluorine-based rubber, or SBR is more preferable. Specific examples include “Evaflex series (EVA, trade name)” manufactured by Mitsui DuPont Polychemical Co., Ltd., EVA manufactured by Nihon Unicar Co., Ltd., and “Evaflex-EEA Series (ethylene-acrylic) manufactured by Mitsui DuPont Polychemical Co., Ltd. Acid copolymer, trade name) ", EEA made by Nihon Unicar," Daiel Latex Series (fluoro rubber, trade name) "by Daikin Industries," TRD-2001 (SBR, trade name) by JSR "EM-400B (SBR, trade name)" manufactured by Zeon Corporation. A cross-linked acrylic resin (self-crosslinking acrylic resin) having a low glass transition temperature and having a structure in which butyl acrylate is a main component and is cross-linked is also preferable.
多孔質膜（Ａ）におけるバインダの含有量は、無機フィラー同士や多孔質膜（Ａ）と多孔質膜（Ｂ）とを良好に接着する観点から、体積比率で、無機フィラー（板状および板状以外の形状のものを含む）の体積を１００としたときに、１以上であることが好ましく、５以上であることがより好ましく、１０以上であることが更に好ましい。ただし、多孔質膜（Ａ）中のバインダ量が多すぎると、バインダによって多孔質膜（Ａ）の空孔が埋められてしまい、イオンの透過性が悪くなって電池特性に悪影響が出る虞がある。よって、多孔質膜（Ａ）におけるバインダの含有量は、体積比率で、無機フィラー（板状および板状以外の形状のものを含む）の体積を１００としたときに、３０以下であることが好ましく、２０以下であることがより好ましい。 The content of the binder in the porous membrane (A) is a volume ratio from the viewpoint of satisfactorily bonding the inorganic fillers or the porous membrane (A) and the porous membrane (B). (Including those other than the shape) is 100, preferably 1 or more, more preferably 5 or more, and even more preferably 10 or more. However, if the amount of the binder in the porous membrane (A) is too large, the pores of the porous membrane (A) are filled with the binder, which may deteriorate the ion permeability and adversely affect the battery characteristics. is there. Therefore, the content of the binder in the porous membrane (A) is 30 or less when the volume of the inorganic filler (including a plate shape and a shape other than the plate shape) is 100 in volume ratio. Preferably, it is 20 or less.
本発明のセパレータにおいて、基材となる多孔質膜（Ｂ）は、融点が１５０℃未満のポリオレフィンと、融点が１５０℃以上のポリオレフィンとの混合物を含んでいる。なお、本明細書でいうポリオレフィンの融点は、ＪＩＳ Ｋ ７１２１の規定に準じて、示差走査熱量計（ＤＳＣ）を用いて測定される融解温度を意味している。 In the separator of the present invention, the porous membrane (B) serving as the substrate contains a mixture of a polyolefin having a melting point of less than 150 ° C. and a polyolefin having a melting point of 150 ° C. or higher. In addition, the melting point of polyolefin as used in this specification means the melting temperature measured using a differential scanning calorimeter (DSC) according to the rule of JIS K7121.
多孔質膜（Ｂ）において、融点が１５０℃未満のポリオレフィンが存在していることで、シャットダウン温度を低く設定できるため、電池の安全性のマージンを確保することが可能となる。融点が１５０℃未満のポリオレフィンの融点としては、８０℃以上であることが好ましく、１００℃以上であることがより好ましく、また、１４０℃以下であることが好ましい。 In the porous membrane (B), since the polyolefin having a melting point of less than 150 ° C. is present, the shutdown temperature can be set low, so that it is possible to ensure a safety margin of the battery. The melting point of the polyolefin having a melting point of less than 150 ° C. is preferably 80 ° C. or more, more preferably 100 ° C. or more, and preferably 140 ° C. or less.
また、多孔質膜（Ｂ）において、融点が１５０℃以上のポリオレフィンが存在していることで、融点が１５０℃未満のポリオレフィンの融点付近の温度下に電池が置かれた場合でも、多孔質膜（Ｂ）中のポリオレフィンの流動が抑制され、ポリオレフィンが被膜として存在できるため、シャットダウン状態を良好に維持できる。その結果、短絡電流が流れ難く、電池の発熱が小さくなるため、安全性が向上する。 Further, since the polyolefin having a melting point of 150 ° C. or higher exists in the porous membrane (B), even when the battery is placed at a temperature near the melting point of the polyolefin having a melting point of less than 150 ° C. Since the flow of the polyolefin in (B) is suppressed and the polyolefin can exist as a film, the shutdown state can be maintained well. As a result, it is difficult for the short-circuit current to flow and the heat generation of the battery is reduced, so that safety is improved.
融点が１５０℃未満のポリオレフィンとしては、ポリエチレン（ＰＥ）が好ましい。また、融点が１５０℃以上のポリオレフィンとしては、ポリプロピレン（ＰＰ）が好ましい。 As the polyolefin having a melting point of less than 150 ° C., polyethylene (PE) is preferable. Further, as the polyolefin having a melting point of 150 ° C. or higher, polypropylene (PP) is preferable.
多孔質膜（Ｂ）は、例えば、融点が１５０℃未満のポリオレフィンと融点が１５０℃以上のポリオレフィンとの混合物を原料とした微多孔膜（例えば、リチウム二次電池用セパレータとして従来から汎用されているポリオレフィン製の微多孔膜と同様の構造の膜）を用いることができる。すなわち、無機フィラーなどを混合したポリオレフィンを用いて形成したフィルムやシートに、一軸または二軸延伸を施して微細な空孔を形成したものなどを用いることができる。また、融点が１５０℃未満のポリオレフィンと融点が１５０℃以上のポリオレフィンとの混合物に、更に他の樹脂を混合し、これを用いてフィルムやシートとし、その後、前記他の樹脂のみを溶解する溶媒中に、これらフィルムやシートを浸漬して、前記他の樹脂のみを溶解させて空孔を形成したものを、多孔質膜（Ｂ）として用いることもできる。よって、多孔質膜（Ｂ）は、例えば、多孔質膜（Ａ）の含有する無機フィラーとして先に例示した各種微粒子を含有していてもよい。 The porous membrane (B) is, for example, conventionally used as a microporous membrane (for example, a separator for a lithium secondary battery) made of a mixture of a polyolefin having a melting point of less than 150 ° C. and a polyolefin having a melting point of 150 ° C. or more. A film having a structure similar to that of a polyolefin microporous film) can be used. That is, it is possible to use a film or sheet formed using a polyolefin mixed with an inorganic filler or the like by forming uniaxial or biaxial stretching to form fine pores. Further, a solvent in which another resin is further mixed with a mixture of a polyolefin having a melting point of less than 150 ° C. and a polyolefin having a melting point of 150 ° C. or more to form a film or sheet, and then only the other resin is dissolved. A film in which these films and sheets are immersed and only the other resin is dissolved to form pores can be used as the porous membrane (B). Therefore, the porous membrane (B) may contain, for example, various fine particles exemplified above as the inorganic filler contained in the porous membrane (A).
なお、多孔質膜（Ｂ）において、融点が１５０℃未満のポリオレフィンと融点が１５０℃以上のポリオレフィンとの使用比率としては、例えば、これらの合計量を１００質量部としたとき、シャットダウン特性を良好に確保する観点から、融点が１５０℃未満のポリオレフィンの量が、５０質量部以上であることが好ましく、６０質量部以上であることがより好ましい（すなわち、融点が１５０℃以上のポリオレフィンの量が、５０質量部以下であることが好ましく、４０質量部以下であることがより好ましい。）。また、電池内において、シャットダウンを生じ、融点が１５０℃未満のポリオレフィンが溶融した際に、そのシャットダウン状態を良好に維持する観点から、多孔質膜（Ｂ）における融点が１５０℃未満のポリオレフィンと融点が１５０℃以上のポリオレフィンとの合計量を１００質量部としたとき、融点が１５０℃以上のポリオレフィンの量が、５質量部以上であることが好ましく、１０質量部以上であることがより好ましい（すなわち、融点が１５０℃未満のポリオレフィンの量が、９５質量部以下であることが好ましく、９０質量部以下であることがより好ましい。）。 In addition, in the porous membrane (B), the use ratio of the polyolefin having a melting point of less than 150 ° C. and the polyolefin having a melting point of 150 ° C. or more, for example, when the total amount thereof is 100 parts by mass, the shutdown characteristics are good. From the viewpoint of ensuring the above, the amount of the polyolefin having a melting point of less than 150 ° C. is preferably 50 parts by mass or more, more preferably 60 parts by mass or more (that is, the amount of the polyolefin having a melting point of 150 ° C. or more). 50 parts by mass or less, and more preferably 40 parts by mass or less. In addition, when a polyolefin having a melting point of less than 150 ° C. is melted in the battery, the polyolefin in the porous membrane (B) has a melting point of less than 150 ° C. When the total amount of the polyolefin having a temperature of 150 ° C. or higher is 100 parts by mass, the amount of the polyolefin having a melting point of 150 ° C. or higher is preferably 5 parts by mass or more, more preferably 10 parts by mass or more ( That is, the amount of polyolefin having a melting point of less than 150 ° C. is preferably 95 parts by mass or less, and more preferably 90 parts by mass or less.
本発明のセパレータは、多孔質膜（Ａ）と多孔質膜（Ｂ）とを、それぞれ１層ずつ有していてもよく、複数有していてもよい。例えば、多孔質膜（Ｂ）の両面に多孔質膜（Ａ）を配置してセパレータを構成したり、多孔質膜（Ａ）の両面に多孔質膜（Ｂ）を配置してセパレータを構成してもよい。ただし、セパレータの有する層数が多くなりすぎると、セパレータの厚みを増やして電池の内部抵抗の増加やエネルギー密度の低下を招く虞があるので好ましくなく、セパレータ中の層数は５層以下であることが好ましい。 The separator of the present invention may have one or more porous membranes (A) and porous membranes (B), respectively. For example, a separator is formed by arranging the porous film (A) on both sides of the porous film (B), or a separator is formed by arranging the porous film (B) on both sides of the porous film (A). May be. However, if the separator has too many layers, it is not preferable because the thickness of the separator is increased, which may increase the internal resistance of the battery and decrease the energy density. The number of layers in the separator is 5 or less. It is preferable.
電池の短絡防止効果をより高め、また、セパレータの強度を確保して、その取り扱い性を良好とする観点から、セパレータの厚みは、例えば、３μｍ以上とすることが好ましく、５μｍ以上とすることがより好ましい。他方、電池のエネルギー密度をより高める観点からは、セパレータの厚みは、５０μｍ以下とすることが好ましく、３０μｍ以下とすることがより好ましい。 The thickness of the separator is preferably 3 μm or more, for example, preferably 5 μm or more, from the viewpoint of further enhancing the effect of preventing short circuiting of the battery and securing the strength of the separator to improve its handleability. More preferred. On the other hand, from the viewpoint of further increasing the energy density of the battery, the thickness of the separator is preferably 50 μm or less, and more preferably 30 μm or less.
また、多孔質膜（Ａ）の厚み［多孔質膜（Ａ）が複数存在する場合には、その合計厚み。多孔質膜（Ａ）の厚みについて、以下同じ。］は、特に限定されないが、例えば、多孔質膜（Ａ）を設けることによる前記の効果をより良好に確保する観点から、１μｍ以上であることが好ましく、２μｍ以上であることがより好ましい。ただし、多孔質膜（Ａ）が厚すぎると、セパレータの厚みを増やして電池のエネルギー密度の低下などを引き起こす虞があることから、その厚みは、１０μｍ以下であることが好ましく、６μｍ以下であることがより好ましい。 Further, the thickness of the porous membrane (A) [when there are a plurality of porous membranes (A), the total thickness thereof. The same applies to the thickness of the porous membrane (A). ] Is not particularly limited, but is preferably 1 μm or more, and more preferably 2 μm or more, for example, from the viewpoint of better securing the above-described effect by providing the porous film (A). However, if the porous membrane (A) is too thick, the thickness of the separator may be increased to cause a decrease in the energy density of the battery. Therefore, the thickness is preferably 10 μm or less, and 6 μm or less. It is more preferable.
更に、多孔質膜（Ｂ）の厚み［多孔質膜（Ｂ）が複数存在する場合には、その合計厚み。多孔質膜（Ｂ）の厚みについて、以下同じ。］は、特に限定されないが、例えば、多孔質膜（Ｂ）を設けることによる前記の効果をより良好に確保する観点から、６μｍ以上であることが好ましく、９μｍ以上であることがより好ましい。ただし、多孔質膜（Ｂ）が厚すぎると、セパレータの厚みを増やして電池のエネルギー密度の低下などを引き起こす虞があることから、その厚みは、５０μｍ以下であることが好ましく、３０μｍ以下であることがより好ましい。 Furthermore, the thickness of the porous membrane (B) [when there are a plurality of porous membranes (B), the total thickness thereof. The same applies to the thickness of the porous membrane (B). ] Is not particularly limited, but is preferably 6 μm or more, and more preferably 9 μm or more, for example, from the viewpoint of better securing the above-described effect by providing the porous film (B). However, if the porous membrane (B) is too thick, the thickness of the separator may be increased to cause a decrease in the energy density of the battery. Therefore, the thickness is preferably 50 μm or less, and 30 μm or less. It is more preferable.
また、セパレータ全体の空孔率としては、有機電解液の保液量を確保してイオン透過性を良好にするために、乾燥した状態で、２０％以上であることが好ましく、３０％以上であることがより好ましい。一方、セパレータ強度の確保と内部短絡の防止の観点から、セパレータの空孔率は、乾燥した状態で、７０％以下であることが好ましく、６０％以下であることがより好ましい。なお、セパレータの空孔率：Ｐ（％）は、セパレータの厚み、面積あたりの質量、構成成分の密度から、下記（１）式を用いて各成分ｉについての総和を求めることにより計算できる。
Ｐ ＝ １００−（Σａｉ／ρｉ）×（ｍ／ｔ） （１）
ここで、前記式中、ａｉ：質量％で表した成分ｉの比率、ρｉ：成分ｉの密度（ｇ／ｃｍ３）、ｍ：セパレータの単位面積あたりの質量（ｇ／ｃｍ２）、ｔ：セパレータの厚み（ｃｍ）である。
Further, the porosity of the separator as a whole is preferably 20% or more, and preferably 30% or more in a dry state, in order to secure a liquid retention amount of the organic electrolyte and improve ion permeability. More preferably. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing internal short circuit, the porosity of the separator is preferably 70% or less, more preferably 60% or less, in a dry state. The porosity of the separator: P (%) can be calculated by obtaining the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula (1).
P = 100− (Σa i / ρ i ) × (m / t) (1)
Here, in the above formula, a i : ratio of component i expressed by mass%, ρ i : density of component i (g / cm 3 ), m: mass per unit area of separator (g / cm 2 ), t: The thickness (cm) of the separator.
また、前記（１）式において、ｍを多孔質膜（Ａ）の単位面積あたりの質量（ｇ／ｃｍ２）とし、ｔを多孔質膜（Ａ）の厚み（ｃｍ）とすることで、前記（１）式を用いて多孔質膜（Ａ）の空孔率：Ｐ（％）を求めることもできる。この方法により求められる多孔質層（Ａ）の空孔率は、例えば、電池の充放電特性を高める観点から、３０％以上であることが好ましく、また、セパレータの収縮抑制作用をより高める観点から、５０％以下であることが好ましい。 In the formula (1), m is the mass per unit area (g / cm 2 ) of the porous membrane (A), and t is the thickness (cm) of the porous membrane (A). The porosity: P (%) of the porous membrane (A) can also be obtained using the equation (1). The porosity of the porous layer (A) required by this method is preferably 30% or more from the viewpoint of improving the charge / discharge characteristics of the battery, for example, and from the viewpoint of further increasing the shrinkage suppression effect of the separator. 50% or less is preferable.
更に、前記（１）式において、ｍを多孔質層（Ｂ）の単位面積あたりの質量（ｇ／ｃｍ２）とし、ｔを多孔質層（Ｂ）の厚み（ｃｍ）とすることで、前記（１）式を用いて多孔質層（Ｂ）の空孔率：Ｐ（％）を求めることもできる。この方法により求められる多孔質層（Ｂ）の空孔率は、２０〜６０％であることが好ましい。 Furthermore, in the formula (1), m is the mass per unit area (g / cm 2 ) of the porous layer (B), and t is the thickness (cm) of the porous layer (B), The porosity: P (%) of the porous layer (B) can also be obtained using the equation (1). It is preferable that the porosity of the porous layer (B) calculated | required by this method is 20 to 60%.
本発明に係るセパレータは、多孔質膜（Ｂ）の含有する融点が１５０℃未満のポリオレフィンの融点以上であって、融点が１５０℃以上のポリオレフィンの融点以下の温度における熱収縮率が、５％以下である。本発明に係るセパレータでは、前記の多孔質層（Ａ）と多孔質層（Ｂ）とを備えることで、このように熱収縮し難いものとなり、高温時におけるセパレータの収縮に基づく電池の短絡を抑制することができる。 The separator according to the present invention has a thermal shrinkage rate of 5% at a temperature not lower than the melting point of the polyolefin having a melting point of less than 150 ° C. and not higher than that of the polyolefin having a melting point of not lower than 150 ° C. It is as follows. In the separator according to the present invention, the provision of the porous layer (A) and the porous layer (B) makes it difficult to thermally shrink in this way, and the short circuit of the battery based on the shrinkage of the separator at a high temperature is prevented. Can be suppressed.
なお、セパレータの前記熱収縮率は、以下の方法により測定される値である。セパレータを縦５ｃｍ、横５ｃｍの正方形に切り取り、黒インクで縦３ｃｍ、横３ｃｍの十字線を描く。なお、前記十字線は、その交点が、セパレータ片の中心となるようにする。その後、セパレータ片を７ｃｍ×７ｃｍのサイズの紙２枚の間に挟み、紙の端をステープラーで止めて固定して試験片とする。前記の試験片を１５０℃に加熱した恒温槽の中で２時間静置し、取り出して冷却した後、十字線のうちのより短い方の長さｄ（ｍｍ）を計測する。そして、下記式によって熱収縮率（％）を算出する。
熱収縮率 ＝ １００×（３０−ｄ）／３０
The thermal shrinkage rate of the separator is a value measured by the following method. The separator is cut into a square of 5 cm in length and 5 cm in width, and a cross line of 3 cm in length and 3 cm in width is drawn with black ink. Note that the intersection of the cross lines is the center of the separator piece. Thereafter, the separator piece is sandwiched between two sheets of 7 cm × 7 cm paper, and the end of the paper is fixed with a stapler to obtain a test piece. The test piece is allowed to stand in a thermostat heated to 150 ° C. for 2 hours, taken out and cooled, and then the shorter length d (mm) of the crosshairs is measured. And a thermal contraction rate (%) is computed by a following formula.
Heat shrinkage rate = 100 × (30−d) / 30
また、本発明に係るセパレータは、ＪＩＳ Ｐ ８１１７に準拠した方法で測定され、０．８７９ｇ／ｍｍ２の圧力下で１００ｍｌの空気が膜を透過する秒数で示されるガーレー値が、１０〜３００ｓｅｃであることが望ましい。透気度が大きすぎると、イオン透過性が小さくなり、透気度が小さすぎると、セパレータの強度が小さくなることがある。 The separator according to the present invention is measured by a method according to JIS P 8117, and has a Gurley value of 10 to 300 sec indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm 2. It is desirable that If the air permeability is too high, the ion permeability is reduced, and if the air permeability is too low, the strength of the separator may be reduced.
本発明のセパレータは、例えば、多孔質膜（Ｂ）を基材とし、その表面に多孔質膜（Ａ）を形成するためのスラリーを塗布し、乾燥する工程を経て製造することができる。 The separator of this invention can be manufactured through the process of apply | coating the slurry for forming a porous membrane (A) on the surface, using the porous membrane (B) as a base material, and drying, for example.
多孔質膜（Ａ）形成用スラリーは、板状の粒子を主体とする前記の無機フィラーの他、必要に応じてバインダなどを含有し、これらを溶媒（分散媒を含む。以下同じ。）に分散させたものである。なお、バインダについては溶媒に溶解させることもできる。多孔質層（Ａ）形成用スラリーに用いられる溶媒は、前記フィラーなどを均一に分散でき、また、バインダを均一に溶解または分散できるものであればよいが、例えば、トルエンなどの芳香族炭化水素、テトラヒドロフランなどのフラン類、メチルエチルケトン、メチルイソブチルケトンなどのケトン類など、一般的な有機溶媒が好適に用いられる。なお、これらの溶媒に、界面張力を制御する目的で、アルコール（エチレングリコール、プロピレングリコールなど）、または、モノメチルアセテートなどの各種プロピレンオキサイド系グリコールエーテルなどを適宜添加してもよい。また、バインダが水溶性である場合、エマルジョンとして使用する場合などでは、水を溶媒としてもよく、この際にもアルコール類（メチルアルコール、エチルアルコール、イソプロピルアルコール、エチレングリコールなど）を適宜加えて界面張力を制御することもできる。 The slurry for forming the porous membrane (A) contains, in addition to the above-described inorganic filler mainly composed of plate-like particles, a binder or the like as necessary, and these are contained in a solvent (including a dispersion medium; the same applies hereinafter). It is dispersed. Note that the binder can be dissolved in a solvent. The solvent used in the slurry for forming the porous layer (A) may be any solvent that can uniformly disperse the filler and the like, and can dissolve or disperse the binder uniformly. For example, an aromatic hydrocarbon such as toluene. Common organic solvents such as francs such as tetrahydrofuran, ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, an alcohol (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) is added as appropriate to the interface. The tension can also be controlled.
多孔質膜（Ａ）形成用スラリーは、前記の無機フィラーおよびバインダを含む固形分含量を、例えば１０〜８０質量％とすることが好ましい。 The slurry for forming the porous membrane (A) preferably has a solid content including the inorganic filler and the binder of, for example, 10 to 80% by mass.
多孔質膜（Ａ）形成用スラリーの塗布に用いる塗工機としては、例えば、ダイコーター、グラビアコーター、リバースロールコーター、スクイズロールコーター、カーテンコーター、ブレードコーター、ナイフコーターなどの、従来から知られている各種塗工機が挙げられる。 As a coating machine used for applying the slurry for forming the porous film (A), for example, a die coater, a gravure coater, a reverse roll coater, a squeeze roll coater, a curtain coater, a blade coater, a knife coater and the like are conventionally known. And various coating machines.
なお、多孔質膜（Ａ）中の板状の無機フィラーの配向性を高めるには、多孔質膜（Ａ）形成用スラリーを基材に塗布する際に、多孔質膜（Ａ）形成用スラリーにシェアをかければよい。多孔質膜（Ａ）形成用スラリーにシェアをかけるには、例えば、多孔質膜（Ａ）形成用スラリーを多孔質膜（Ｂ）の表面に塗布した後、一定のギャップを通して余分なスラリーを除去し、その後乾燥するなどの工程を経ればよい。 In order to enhance the orientation of the plate-like inorganic filler in the porous membrane (A), the slurry for forming the porous membrane (A) is applied when the slurry for forming the porous membrane (A) is applied to the substrate. Share it with. To share the slurry for forming the porous membrane (A), for example, after applying the slurry for forming the porous membrane (A) to the surface of the porous membrane (B), remove excess slurry through a certain gap. Then, a process such as drying may be performed.
また、多孔質膜（Ａ）中の板状の無機フィラーの配向性をより高めるには、前記のシェアをかける方法以外にも、高固形分濃度（例えば５０〜８０質量％）の多孔質膜（Ａ）形成用スラリーを使用する方法；板状の無機フィラーを、ディスパー、アジター、ホモジナイザー、ボールミル、アトライター、ジェットミルなどの各種混合・攪拌装置、分散装置などを用いて溶媒に分散させ、得られた分散体にバインダなどを添加・混合して調製した多孔質膜（Ａ）形成用スラリーを使用する方法；表面に油脂類、界面活性剤、シランカップリング剤などの分散剤を作用させて、表面を改質した板状の無機フィラーを用いて調製した多孔質膜（Ａ）形成用スラリーを使用する方法；形状、径またはアスペクト比の異なる板状の無機フィラーを併用して調製した多孔質膜（Ａ）形成用スラリーを使用する方法；多孔質膜（Ａ）形成用スラリーを多孔質膜（Ｂ）に塗布した後の乾燥条件を制御する方法；セパレータを加圧や加熱加圧プレスする方法；多孔質膜（Ａ）形成用スラリーを多孔質膜（Ｂ）に塗布した後、乾燥前に磁場をかける方法；などが採用でき、これらの方法をそれぞれ単独で実施してもよく、２種以上の方法を組み合わせて実施してもよい。 Moreover, in order to further enhance the orientation of the plate-like inorganic filler in the porous membrane (A), a porous membrane having a high solid content concentration (for example, 50 to 80% by mass) other than the method of applying the above-mentioned share. (A) A method using a forming slurry; a plate-like inorganic filler is dispersed in a solvent using various mixing / stirring devices such as a disper, an agitator, a homogenizer, a ball mill, an attritor, a jet mill, a dispersing device, A method of using a slurry for forming a porous membrane (A) prepared by adding and mixing a binder to the obtained dispersion; a dispersant such as oils and fats, a surfactant, a silane coupling agent is allowed to act on the surface Using a slurry for forming a porous film (A) prepared using a plate-like inorganic filler whose surface has been modified; using a plate-like inorganic filler having a different shape, diameter or aspect ratio in combination. Method of using the prepared slurry for forming the porous membrane (A); Method of controlling the drying conditions after applying the slurry for forming the porous membrane (A) to the porous membrane (B); Pressurizing and heating the separator A method of pressing under pressure; a method of applying a magnetic field before drying after applying the slurry for forming the porous membrane (A) to the porous membrane (B); and the like can be employed. Alternatively, two or more methods may be combined.
本発明のリチウム二次電池は、本発明のセパレータを有していればよく、その他の構成および構造については特に制限はなく、従来から知られているリチウム二次電池で採用されている構成および構造を適用することができる。 The lithium secondary battery of the present invention only needs to have the separator of the present invention, and there are no particular restrictions on the other configurations and structures, and the configurations and configurations adopted in conventionally known lithium secondary batteries Structure can be applied.
リチウム二次電池の形態としては、スチール缶やアルミニウム缶などを外装缶として使用した筒形（角筒形や円筒形）などが挙げられる。また、金属を蒸着したラミネートフィルムを外装体としたソフトパッケージ電池とすることもできる。 Examples of the form of the lithium secondary battery include a cylindrical shape (a square cylindrical shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.
正極としては、従来から知られているリチウム二次電池に用いられている正極、すなわち、Ｌｉイオンを吸蔵放出可能な活物質を含有する正極であれば特に制限はない。例えば、活物質として、Ｌｉ１＋ｘＭＯ２（−０．１＜ｘ＜０．１、Ｍ：Ｃｏ、Ｎｉ、Ｍｎなど）で表されるリチウム含有遷移金属酸化物；ＬｉＭｎ２Ｏ４などのリチウムマンガン酸化物；ＬｉＭｎ２Ｏ４のＭｎの一部を他元素で置換したＬｉＭｎｘＭ（１−ｘ）Ｏ２；オリビン型ＬｉＭＰＯ４（Ｍ：Ｃｏ、Ｎｉ、Ｍｎ、Ｆｅ）；ＬｉＭｎ０．５Ｎｉ０．５Ｏ２；Ｌｉ（１＋ａ）ＭｎｘＮｉｙＣｏ（１−ｘ−ｙ）Ｏ２(−０．１＜ａ＜０．１、０＜ｘ＜０．５、０＜ｙ＜０．５)；などを適用することが可能であり、これらの正極活物質に公知の導電助剤（カーボンブラックなどの炭素材料など）やポリフッ化ビニリデン（ＰＶＤＦ）などの結着剤などを適宜添加した正極合剤を、集電体を芯材として成形体（すなわち、正極合剤層）に仕上げたものなどを用いることができる。 The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known lithium secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing Li ions. For example, as an active material, lithium-containing transition metal oxide represented by Li 1 + x MO 2 (−0.1 <x <0.1, M: Co, Ni, Mn, etc.); lithium manganese such as LiMn 2 O 4 Oxide; LiMn x M (1-x) O 2 in which part of Mn of LiMn 2 O 4 is substituted with another element; olivine type LiMPO 4 (M: Co, Ni, Mn, Fe); LiMn 0.5 Ni 0.5 O 2 ; Li (1 + a) Mn x Ni y Co (1-xy) O 2 (−0.1 <a <0.1, 0 <x <0.5, 0 <y <0. 5); can be applied, and a known conductive additive (carbon material such as carbon black) or a binder such as polyvinylidene fluoride (PVDF) is appropriately added to these positive electrode active materials. The positive electrode mixture is formed from a current collector as a core material (ie, Such as those finished electrode mixture layer) may be used.
正極の集電体としては、アルミニウムなどの金属の箔、パンチングメタル、網、エキスパンドメタルなどを用い得るが、通常、厚みが１０〜３０μｍのアルミニウム箔が好適に用いられる。 As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is preferably used.
正極側のリード部は、通常、正極作製時に、集電体の一部に正極合剤層を形成せずに集電体の露出部を残し、そこをリード部とすることによって設けられる。ただし、リード部は必ずしも当初から集電体と一体化されたものであることは要求されず、集電体にアルミニウム製の箔などを後から接続することによって設けてもよい。 The lead portion on the positive electrode side is normally provided by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead portion at the time of producing the positive electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.
負極としては、従来から知られているリチウム二次電池に用いられている負極、すなわち、Ｌｉイオンを吸蔵放出可能な活物質を含有する負極であれば特に制限はない。例えば、活物質として、黒鉛、熱分解炭素類、コークス類、ガラス状炭素類、有機高分子化合物の焼成体、メソカーボンマイクロビーズ（ＭＣＭＢ）、炭素繊維などの、リチウムを吸蔵、放出可能な炭素系材料の１種または２種以上の混合物が用いられる。また、Ｓｉ，Ｓｎ、Ｇｅ，Ｂｉ，Ｓｂ、Ｉｎなどの元素およびその合金、リチウム含有窒化物、または酸化物などのリチウム金属に近い低電圧で充放電できる化合物、もしくはリチウム金属やリチウム／アルミニウム合金も負極活物質として用いることができる。負極には、これらの負極活物質に導電助剤（カーボンブラックなどの炭素材料など）やＰＶＤＦなどの結着剤などを適宜添加した負極合剤を、集電体を芯材として成形体（負極合剤層）に仕上げたものや、前記の各種合金やリチウム金属の箔を単独で用いたり、前記合金やリチウム金属の層を集電体表面に形成したものなどの負極剤層を有するものが用いられる。 The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known lithium secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions. For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and their alloys, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. For the negative electrode, a negative electrode mixture in which a conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these negative electrode active materials, and a molded body (negative electrode) using the current collector as a core material Those having a negative electrode agent layer, such as those obtained by finishing the mixture layer), using the above-mentioned various alloys and lithium metal foils alone, or forming the alloy or lithium metal layer on the surface of the current collector Used.
負極に集電体を用いる場合には、集電体としては、銅製やニッケル製の箔、パンチングメタル、網、エキスパンドメタルなどを用い得るが、通常、銅箔が用いられる。この負極集電体は、高エネルギー密度の電池を得るために負極全体の厚みを薄くする場合、厚みの上限は３０μｍであることが好ましく、また、下限は５μｍであることが望ましい。 When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.
負極側のリード部も、正極側のリード部と同様に、通常、負極作製時に、集電体の一部に負極剤層（負極活物質を有する層、負極合剤層を含む）を形成せずに集電体の露出部を残し、そこをリード部とすることによって設けられる。ただし、この負極側のリード部は必ずしも当初から集電体と一体化されたものであることは要求されず、集電体に銅製の箔などを後から接続することによって設けてもよい。 As with the lead portion on the negative electrode side, the negative electrode layer (including a layer having a negative electrode active material and a negative electrode mixture layer) is usually formed on a part of the current collector during the preparation of the negative electrode. Without leaving the exposed portion of the current collector, it is provided as a lead portion. However, the lead portion on the negative electrode side is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.
電極は、前記の正極と前記の負極とを、本発明に係るセパレータを介して積層した積層体や、更にこれを巻回した電極巻回体の形態で用いることができる。 The electrode can be used in the form of a laminate obtained by laminating the positive electrode and the negative electrode via the separator according to the present invention, or an electrode wound body obtained by winding the laminate.
電解液（有機電解液）としては、リチウム塩を有機溶媒に溶解した溶液が用いられる。リチウム塩としては、溶媒中で解離してＬｉ＋イオンを形成し、電池として使用される電圧範囲で分解などの副反応を起こさないものであれば特に制限はない。例えば、ＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＡｓＦ６、ＬｉＳｂＦ６ などの無機リチウム塩；ＬｉＣＦ３ＳＯ３、ＬｉＣＦ３ＣＯ２、Ｌｉ２Ｃ２Ｆ４（ＳＯ３）２、ＬｉＮ（ＣＦ３ＳＯ２）２、ＬｉＣ（ＣＦ３ＳＯ２）３、ＬｉＣｎＦ２ｎ＋１ＳＯ３（ｎ≧２）、ＬｉＮ（ＲｆＯＳＯ２）２〔ここでＲｆはフルオロアルキル基〕などの有機リチウム塩；などを用いることができる。 As the electrolytic solution (organic electrolytic solution), a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li + ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 ; LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiN (CF 3 SO 2 ) 2 , LiC (CF 3 SO 2 ) 3 , LiC n F 2n + 1 SO 3 (n ≧ 2), LiN (RfOSO 2 ) 2 [where Rf is a fluoroalkyl group]; it can.
電解液に用いる有機溶媒としては、前記のリチウム塩を溶解し、電池として使用される電圧範囲で分解などの副反応を起こさないものであれば特に限定されない。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、ビニレンカーボネートなどの環状カーボネート；ジメチルカーボネート、ジエチルカーボネート、メチルエチルカーボネートなどの鎖状カーボネート；プロピオン酸メチルなどの鎖状エステル；γ−ブチロラクトンといった環状エステル；ジメトキシエタン、ジエチルエーテル、１，３−ジオキソラン、ジグライム、トリグライム、テトラグライムなどの鎖状エーテル；ジオキサン、テトラヒドロフラン、２−メチルテトラヒドロフランなどの環状エーテル；アセトニトリル、プロピオニトリル、メトキシプロピオニトリルといったニトリル類；エチレングリコールサルファイトなどの亜硫酸エステル類；などが挙げられ、これらを１種単独で用いてもよいし、２種以上を併用しても構わない。なお、より良好な特性の電池とするためには、エチレンカーボネートと鎖状カーボネートの混合溶媒など、高い導電率を得ることができる組み合わせで用いることが望ましい。また、これらの電解液に安全性や充放電サイクル性、高温貯蔵性といった特性を向上させる目的で、ビニレンカーボネート類、１，３−プロパンサルトン、ジフェニルジスルフィド、シクロヘキシルベンゼン、ビフェニル、フルオロベンゼン、ｔ−ブチルベンゼンなどの添加剤を適宜加えることもできる。 The organic solvent used in the electrolytic solution is not particularly limited as long as it dissolves the lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as ethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfites such as ethylene glycol sulfite; and the like, and these may be used alone. , It may be used in combination of two or more thereof. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, biphenyl, fluorobenzene, t are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. -Additives such as butylbenzene can be added as appropriate.
このリチウム塩の電解液中の濃度としては、０．５〜１．５ｍｏｌ／ｌとすることが好ましく、０．９〜１．２５ｍｏｌ／ｌとすることがより好ましい。 The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.
また、前記の有機溶媒の代わりに、エチル−メチルイミダゾリウムトリフルオロメチルスルホニウムイミド、へプチル−トリメチルアンモニウムトリフルオロメチルスルホニウムイミド、ピリジニウムトリフルオロメチルスルホニウムイミド、グアジニウムトリフルオロメチルスルホニウムイミドといった常温溶融塩を用いることもできる。 Also, instead of the organic solvent, melting at room temperature such as ethyl-methylimidazolium trifluoromethylsulfonium imide, heptyl-trimethylammonium trifluoromethylsulfonium imide, pyridinium trifluoromethylsulfonium imide, guanidinium trifluoromethylsulfonium imide A salt can also be used.
更に、前記の電解液を含有してゲル化するような高分子材料を添加して、電解液をゲル状にして電池に用いてもよい。電解液をゲル状とするための高分子材料としては、ＰＶＤＦ、フッ化ビニリデン−ヘキサフルオロプロピレン共重合体（ＰＶＤＦ−ＨＦＰ）、ＰＡＮ、ポリエチレンオキシド、ポリプロピレンオキシド、エチレンオキシド−プロピレンオキシド共重合体、主鎖または側鎖にエチレンオキシド鎖を有する架橋ポリマー、架橋したポリ（メタ）アクリル酸エステルなど、公知のゲル状電解質形成可能なホストポリマーが挙げられる。 Furthermore, a polymer material that contains the electrolytic solution and gels may be added, and the electrolytic solution may be gelled and used for the battery. Polymer materials for making the electrolyte into a gel include PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), PAN, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, main Examples of the host polymer capable of forming a known gel electrolyte such as a cross-linked polymer having an ethylene oxide chain in a chain or a side chain, and a cross-linked poly (meth) acrylic ester.
本発明のリチウム二次電池は、携帯電話やノート型パーソナルコンピューターなどの各種携帯機器などの電子機器の電源用途を始めとして、従来から知られているリチウム二次電池が用いられている各種用途と同じ用途に適用することができる。 The lithium secondary battery of the present invention includes various uses in which a conventionally known lithium secondary battery is used, including power supply applications for electronic devices such as various portable devices such as mobile phones and notebook personal computers. It can be applied to the same application.
以下、実施例に基づいて本発明を詳細に述べる。ただし、下記実施例は、本発明を制限するものではない。 Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.
実施例１
＜セパレータの作製＞
無機フィラーである板状ベーマイト（平均粒径１μｍ、アスペクト比１０）１０００ｇに、水１０００ｇと、板状ベーマイト１００質量部に対して１質量部のポリアクリル酸アンモニウム（分散剤）とを添加し、これを卓上ボールミルにて６日間分散を行った後、バインダである自己架橋性のアクリル樹脂のエマルジョン（アクリル樹脂量が、板状ベーマイト１００質量部に対して３質量部）を添加し、更に、増粘剤としてキサンタンガムを２ｇ添加し、スリーワンモーターで１時間攪拌して分散させて、均一な多孔質膜（Ａ）形成用スラリーを得た。得られたスラリーの粘度を、Ｅ型粘度計を用い、２０℃で測定したところ、２００ｍＰａ・ｓであった。
Example 1
<Preparation of separator>
To 1000 g of plate-like boehmite (average particle size 1 μm, aspect ratio 10), which is an inorganic filler, 1000 g of water and 1 part by mass of ammonium polyacrylate (dispersant) with respect to 100 parts by mass of plate-like boehmite, After dispersing this for 6 days in a table-top ball mill, a binder self-crosslinking acrylic resin emulsion (the amount of the acrylic resin is 3 parts by mass with respect to 100 parts by mass of plate boehmite) is added. 2 g of xanthan gum was added as a thickener, and the mixture was stirred and dispersed with a three-one motor for 1 hour to obtain a uniform slurry for forming a porous membrane (A). It was 200 mPa * s when the viscosity of the obtained slurry was measured at 20 degreeC using the E-type viscosity meter.
ポリオレフィン製多孔性フィルム［多孔質膜（Ｂ）、厚み１６μｍ、空孔率４０％］の片面に、前記のスラリーを塗布し、乾燥して、厚みが４μｍの多孔質膜（Ａ）を形成して、セパレータを得た。なお、前記のポリオレフィン製多孔性フィルムは、前記のＤＳＣによる融解温度測定法によって測定を行うと、１３５℃にＰＥの融点由来の吸熱ピークと、１５５℃にＰＰの融点由来の吸熱ピークとが観測され、これらＰＥとＰＰとの混合物を原料とするものであり、ＰＥとＰＰとの合計を１００質量部としたとき、ＰＥが８５質量部（ＰＰが１５質量部）である。 The slurry is applied to one side of a polyolefin porous film [porous membrane (B), thickness 16 μm, porosity 40%] and dried to form a porous membrane (A) having a thickness of 4 μm. Thus, a separator was obtained. The polyolefin porous film has an endothermic peak derived from the melting point of PE at 135 ° C. and an endothermic peak derived from the melting point of PP at 155 ° C. when measured by the melting temperature measurement method using DSC. A mixture of PE and PP is used as a raw material. When the total of PE and PP is 100 parts by mass, PE is 85 parts by mass (PP is 15 parts by mass).
＜正極の作製＞
正極活物質であるＬｉＣｏＯ２：８５質量部、導電助剤であるアセチレンブラック：１０質両部、およびバインダであるＰＶＤＦ：５質量部を、Ｎ−メチル−２−ピロリドン（ＮＭＰ）を溶剤として均一になるように混合して、正極合剤含有ペーストを調製した。このペーストを、集電体となる厚さ１５μｍのアルミニウム箔の両面に、塗布長が表面３２０ｍｍ、裏面２５０ｍｍになるように間欠塗布し、乾燥した後、カレンダー処理を行って、全厚が１５０μｍになるように正極合剤層の厚みを調整し、幅４３ｍｍになるように切断して、長さ３４０ｍｍ、幅４３ｍｍの正極を作製した。更に、この正極のアルミニウム箔の露出部にリード体を取り付けた。
<Preparation of positive electrode>
85 parts by mass of LiCoO 2 as a positive electrode active material, 10 parts by mass of acetylene black as a conductive additive, and 5 parts by mass of PVDF as a binder, uniformly using N-methyl-2-pyrrolidone (NMP) as a solvent Was mixed to prepare a positive electrode mixture-containing paste. This paste is intermittently applied on both sides of a 15 μm thick aluminum foil serving as a current collector so that the coating length is 320 mm on the front surface and 250 mm on the back surface, dried, and calendered to a total thickness of 150 μm. Thus, the thickness of the positive electrode mixture layer was adjusted, and the positive electrode mixture layer was cut to have a width of 43 mm to produce a positive electrode having a length of 340 mm and a width of 43 mm. Furthermore, the lead body was attached to the exposed part of the aluminum foil of this positive electrode.
＜負極の作製＞
負極活物質である黒鉛：９５質量部、およびバインダであるＰＶＤＦ：５質量部を、ＮＭＰを溶剤として均一になるように混合して、負極合剤含有ペーストを調製した。このペーストを、集電体となる厚さ１０μｍの銅箔の両面に、塗布長が表面３２０ｍｍ、裏面２６０ｍｍになるように間欠塗布し、乾燥した後、カレンダー処理を行って、全厚が１４２μｍになるように負極合剤層の厚みを調整し、幅４５ｍｍになるように切断して、長さ３３０ｍｍ、幅４５ｍｍの負極を作製した。更に、この負極の銅箔の露出部にリード体を取り付けた。
<Production of negative electrode>
A negative electrode mixture-containing paste was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This paste is intermittently applied to both sides of a 10 μm thick copper foil serving as a current collector so that the coating length is 320 mm on the front surface and 260 mm on the back surface, dried and calendered to a total thickness of 142 μm. The thickness of the negative electrode mixture layer was adjusted so that the width was 45 mm, and a negative electrode having a length of 330 mm and a width of 45 mm was produced. Furthermore, the lead body was attached to the exposed part of the copper foil of this negative electrode.
＜電池の組み立て＞
前記のようにして得られた正極と負極との間に、前記のセパレータを、多孔質膜（Ａ）が正極側を向くように介在させつつ重ね合わせ、渦巻状に巻回して電極巻回体とした。この電極体を、直径１４ｍｍ、高さ５０ｍｍの有底円筒形の電池ケース（外装缶）内に挿入し、有機電解液（エチレンカーボネートとエチルメチルカーボネートとを１：２の体積比で混合した溶媒に、ＬｉＰＦ６を１．２ｍｏｌ／ｌの濃度で溶解させた溶液）を注入し、電池ケースの開口部を常法に従って封止して、リチウム二次電池を作製した。電池組み立て後の予備充電（化成時充電）では、電池の定格容量７５０ｍＡｈに対して２０％に当たる電気量となるように、１５０ｍＡで４．２Ｖまでの定電流充電と、その後４．２Ｖでの定電圧充電とを、合計６時間行い、その後、１５０ｍＡで３Ｖまで定電流放電を行った。
<Battery assembly>
Between the positive electrode and the negative electrode obtained as described above, the separator is overlapped with the porous membrane (A) facing the positive electrode, and wound in a spiral shape to form an electrode winding body. It was. This electrode body was inserted into a bottomed cylindrical battery case (external can) having a diameter of 14 mm and a height of 50 mm, and an organic electrolyte (a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2). Then, a solution in which LiPF 6 was dissolved at a concentration of 1.2 mol / l) was injected, and the opening of the battery case was sealed according to a conventional method to produce a lithium secondary battery. In the pre-charging after battery assembly (charging at the time of chemical formation), constant current charging up to 4.2V at 150mA and then constant voltage at 4.2V so that the amount of electricity is 20% of the rated capacity of 750mAh. Voltage charging was performed for a total of 6 hours, and then a constant current discharge was performed up to 3 V at 150 mA.
実施例２
板状ベーマイトを、平均粒径が０．６μｍで、アスペクト比が２０のものに変更した以外は、実施例１と同様にして多孔質膜（Ａ）形成用スラリーを調製した。得られたスラリーについて、実施例１と同様にして測定した粘度は、３５ｍＰａ・ｓであった。
Example 2
A slurry for forming a porous membrane (A) was prepared in the same manner as in Example 1 except that the plate boehmite was changed to one having an average particle size of 0.6 μm and an aspect ratio of 20. About the obtained slurry, the viscosity measured in the same manner as in Example 1 was 35 mPa · s.
前記の多孔質膜（Ａ）形成用スラリーを用いた以外は、実施例１と同様にしてセパレータを作製し、このセパレータを用いた以外は、実施例１と同様にしてリチウム二次電池を作製した。 A separator was prepared in the same manner as in Example 1 except that the slurry for forming the porous membrane (A) was used, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used. did.
実施例３
板状ベーマイトに代えて、板状アルミナ（平均粒径０．６μｍ、アスペクト比１０）を用いた以外は、実施例１と同様にして多孔質膜（Ａ）形成用スラリーを調製した。得られたスラリーについて、実施例１と同様にして測定した粘度は、５０ｍＰａ・ｓであった。
Example 3
A slurry for forming a porous membrane (A) was prepared in the same manner as in Example 1 except that plate-like alumina (average particle size 0.6 μm, aspect ratio 10) was used instead of plate-like boehmite. About the obtained slurry, the viscosity measured like Example 1 was 50 mPa * s.
前記の多孔質膜（Ａ）形成用スラリーを用いた以外は、実施例１と同様にしてセパレータを作製し、このセパレータを用いた以外は、実施例１と同様にしてリチウム二次電池を作製した。 A separator was prepared in the same manner as in Example 1 except that the slurry for forming the porous membrane (A) was used, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used. did.
実施例４
板状ベーマイトに代えて、板状シリカ（平均粒径４μｍ、アスペクト比３５）を用いた以外は、実施例１と同様にして多孔質膜（Ａ）形成用スラリーを調製した。得られたスラリーについて、実施例１と同様にして測定した粘度は、１５ｍＰａ・ｓであった。
Example 4
A slurry for forming a porous membrane (A) was prepared in the same manner as in Example 1 except that plate-like silica (average particle size 4 μm, aspect ratio 35) was used instead of plate-like boehmite. About the obtained slurry, the viscosity measured in the same manner as in Example 1 was 15 mPa · s.
前記の多孔質膜（Ａ）形成用スラリーを用いた以外は、実施例１と同様にしてセパレータを作製し、このセパレータを用いた以外は、実施例１と同様にしてリチウム二次電池を作製した。 A separator was prepared in the same manner as in Example 1 except that the slurry for forming the porous membrane (A) was used, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used. did.
実施例５
多孔質膜（Ｂ）とするポリオレフィン製多孔性フィルムを、ＰＥとＰＰとの合計を１００質量部としたときに、ＰＥが６０質量部（ＰＰが４０質量部）で含むＰＥとＰＰとの混合物を原料とするものに変更した以外は、実施例１と同様にしてセパレータを作製した。なお、実施例５で用いたポリオレフィン製多孔性フィルムは、厚みが１６μｍ、空孔率が４０％である。
Example 5
A mixture of PE and PP containing 60 parts by mass of PE (40 parts by mass of PP) when the total amount of PE and PP is 100 parts by mass of the polyolefin porous film used as the porous membrane (B) A separator was prepared in the same manner as in Example 1 except that the material was changed to a material that was used as a raw material. The polyolefin porous film used in Example 5 has a thickness of 16 μm and a porosity of 40%.
前記のセパレータを用いた以外は、実施例１と同様にしてリチウム二次電池を作製した。 A lithium secondary battery was produced in the same manner as in Example 1 except that the separator was used.
比較例１
実施例１と同様にして調製した多孔質膜（Ａ）形成用スラリーを、ポリオレフィン製多孔性フィルム［多孔質膜（Ｂ）、厚み１６μｍ、空孔率４０％］の片面に塗布し、乾燥して、厚みが４μｍの多孔質膜（Ａ）を形成して、セパレータを得た。なお、前記のポリオレフィン製多孔性フィルムは、前記のＤＳＣによる融解温度測定法によって測定を行うと、１３５℃にＰＥの融点由来の吸熱ピークのみが観測され、ＰＰを含まないフィルムである。
Comparative Example 1
The slurry for forming a porous membrane (A) prepared in the same manner as in Example 1 was applied to one side of a polyolefin porous film [porous membrane (B), thickness 16 μm, porosity 40%] and dried. Then, a porous film (A) having a thickness of 4 μm was formed to obtain a separator. In addition, when the said porous film made from polyolefin is measured by the melting temperature measuring method by said DSC, only the endothermic peak derived from melting | fusing point of PE is observed at 135 degreeC, and is a film which does not contain PP.
前記のセパレータを用いた以外は、実施例１と同様にしてリチウム二次電池を作製し、予備充電および放電を行った。 A lithium secondary battery was produced in the same manner as in Example 1 except that the separator was used, and precharge and discharge were performed.
比較例２
実施例１で使用したものと同じポリオレフィン製多孔性フィルムを、多孔質膜（Ａ）を形成することなくセパレータとして用いた以外は、実施例１と同様にしてリチウム二次電池を作製し、予備充電および放電を行った。
Comparative Example 2
A lithium secondary battery was prepared in the same manner as in Example 1 except that the same polyolefin porous film as used in Example 1 was used as a separator without forming the porous membrane (A). Charging and discharging were performed.
なお、前記実施例および比較例の電池は、前記と同様の条件で定電流−定電圧充電および定電流放電を行った場合、約７５０ｍＡｈの容量を示すものである。 In addition, the battery of the said Example and a comparative example shows the capacity | capacitance of about 750 mAh, when performing constant current-constant voltage charge and constant current discharge on the conditions similar to the above.
実施例１〜５および比較例１、２のセパレータについて、下記の熱収縮試験を行った。 The separators of Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to the following heat shrinkage test.
＜熱収縮試験＞
実施例１〜５および比較例１、２の各セパレータについて、前記の方法によって熱収縮率を測定した。なお、熱収縮率は、各実施例、比較例とも３回測定し、その平均値を求めた。
<Heat shrinkage test>
About each separator of Examples 1-5 and Comparative Examples 1 and 2, the thermal contraction rate was measured by the said method. The thermal shrinkage rate was measured three times for each example and comparative example, and the average value was obtained.
また、実施例１〜５および比較例１、２のリチウム二次電池について、下記のオーブン試験を行った。 Moreover, the following oven test was done about the lithium secondary battery of Examples 1-5 and Comparative Examples 1 and 2.
＜オーブン試験＞
実施例１〜５および比較例１、２のリチウム二次電池について、１２００ｍＡで４．２Ｖまでの定電流充電と、その後４．２Ｖでの定電圧充電を、合計２．５時間行った。充電状態の各電池の表面に熱電対を貼り付けた後、防爆の恒温槽内に入れ、槽内温度を、２５℃から１５０℃まで５℃／分の速度で上昇させ、更に１５０℃で３時間保持したときの、各電池の表面温度を測定した。
<Oven test>
The lithium secondary batteries of Examples 1 to 5 and Comparative Examples 1 and 2 were subjected to constant current charging up to 4.2 V at 1200 mA and then constant voltage charging at 4.2 V for a total of 2.5 hours. After attaching a thermocouple to the surface of each battery in a charged state, it is placed in an explosion-proof thermostat, and the temperature in the bath is increased from 25 ° C. to 150 ° C. at a rate of 5 ° C./min. The surface temperature of each battery was measured when held for a period of time.
前記のセパレータの熱収縮試験およびリチウム二次電池のオーブン試験の結果を表１に示す。 Table 1 shows the results of the heat shrink test of the separator and the oven test of the lithium secondary battery.
なお、表１における「多孔質膜（Ｂ）の構成樹脂」の欄に記載の「ＰＥ＋ＰＰ」は、多孔質膜（Ｂ）の構成樹脂が、ＰＥとＰＰとであることを意味している。 In addition, “PE + PP” described in the column “Component resin of porous membrane (B)” in Table 1 means that the constituent resins of the porous membrane (B) are PE and PP.
表１から明らかなように、ＰＥとＰＰとの混合物を含む多孔質膜（Ｂ）の表面に耐熱性を有する多孔質膜（Ａ）を形成して構成した実施例１〜５のセパレータは、熱収縮率が小さく、また、このセパレータを用いた実施例１〜５のリチウム二次電池は、オーブン試験での温度上昇が小さく熱安定性に優れており、良好な安全性を有している。すなわち、実施例１〜５のリチウム二次電池では、オーブン試験時に、良好にシャットダウンを生じており、かつそのシャットダウン状態が良好に維持しているといえる。 As is apparent from Table 1, the separators of Examples 1 to 5 configured by forming the heat-resistant porous film (A) on the surface of the porous film (B) containing a mixture of PE and PP are as follows: The lithium secondary batteries of Examples 1 to 5 using this separator have a small heat shrinkage, have a small temperature rise in the oven test, have excellent thermal stability, and have good safety. . That is, it can be said that the lithium secondary batteries of Examples 1 to 5 are well shut down during the oven test, and the shutdown state is well maintained.
これに対し、ＰＥのみを含む多孔質膜（Ｂ）の表面に多孔質膜（Ａ）を形成して構成した比較例１のセパレータは、熱収縮率は実施例１のセパレータと同等程度に小さいが、このセパレータを用いた比較例１のリチウム二次電池では、オーブン試験での温度上昇が実施例１の電池よりも大きい。また、多孔質膜（Ａ）を有しない比較例２のセパレータは、熱収縮率が大きく、更に、このセパレータを用いた比較例２のリチウム二次電池では、オーブン試験での結果が劣っている。 In contrast, the separator of Comparative Example 1 configured by forming the porous film (A) on the surface of the porous film (B) containing only PE has a thermal contraction rate as small as that of the separator of Example 1. However, in the lithium secondary battery of Comparative Example 1 using this separator, the temperature rise in the oven test is larger than that of the battery of Example 1. Moreover, the separator of Comparative Example 2 that does not have the porous membrane (A) has a large thermal shrinkage rate. Further, in the lithium secondary battery of Comparative Example 2 using this separator, the results of the oven test are inferior. .
Claims (5)
前記多孔質膜（Ａ）の含有する前記無機フィラーは、板状の粒子が主体であり、
前記多孔質膜（Ｂ）における前記ポリオレフィンが、融点が１５０℃未満のポリオレフィンと、融点が１５０℃以上のポリオレフィンとの混合物であり、
前記多孔質膜（Ｂ）の含有する融点が１５０℃未満のポリオレフィンの融点以上であって、融点が１５０℃以上のポリオレフィンの融点以下の温度における熱収縮率が、５％以下であることを特徴とする電池用セパレータ。 It has a porous membrane (A) containing at least an inorganic filler and a porous membrane (B) mainly composed of polyolefin, and the porous membrane (A) and the porous membrane (B) are integrated. Battery separator,
The inorganic filler contained in the porous membrane (A) is mainly composed of plate-like particles,
The polyolefin in the porous membrane (B) is a mixture of a polyolefin having a melting point of less than 150 ° C and a polyolefin having a melting point of 150 ° C or higher,
The melting point contained in the porous membrane (B) is not less than the melting point of a polyolefin having a temperature of less than 150 ° C., and the thermal shrinkage rate at a temperature not exceeding the melting point of the polyolefin having a melting point of not less than 150 ° C. Battery separator.
前記セパレータが、請求項１〜４のいずれかに記載の電池用セパレータであることを特徴とするリチウム二次電池。 A lithium secondary battery comprising a positive electrode containing an active material capable of occluding and releasing Li ions, a negative electrode containing an active material capable of occluding and releasing Li ions, an organic electrolyte, and a separator,
The lithium secondary battery, wherein the separator is the battery separator according to any one of claims 1 to 4.
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| JP2012048932A (en) * | 2010-08-26 | 2012-03-08 | Hitachi Ltd | Lithium ion secondary battery |
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