JP2017212111A - Nonaqueous electrolyte secondary battery - Google Patents
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- JP2017212111A JP2017212111A JP2016104608A JP2016104608A JP2017212111A JP 2017212111 A JP2017212111 A JP 2017212111A JP 2016104608 A JP2016104608 A JP 2016104608A JP 2016104608 A JP2016104608 A JP 2016104608A JP 2017212111 A JP2017212111 A JP 2017212111A
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- 239000011255 nonaqueous electrolyte Substances 0.000 title claims abstract description 124
- 239000007774 positive electrode material Substances 0.000 claims abstract description 109
- 239000007773 negative electrode material Substances 0.000 claims abstract description 42
- 239000000463 material Substances 0.000 claims abstract description 39
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 34
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims abstract description 30
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- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 12
- 229910052744 lithium Inorganic materials 0.000 claims description 11
- -1 lithium transition metal Chemical class 0.000 claims description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 8
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 8
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 8
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- 150000003624 transition metals Chemical class 0.000 claims description 3
- 229910017052 cobalt Inorganic materials 0.000 claims description 2
- 239000010941 cobalt Substances 0.000 claims description 2
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 2
- 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 claims description 2
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- 230000000694 effects Effects 0.000 description 2
- 239000008151 electrolyte solution Substances 0.000 description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
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- 239000005486 organic electrolyte Substances 0.000 description 2
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- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- 229910013063 LiBF 4 Inorganic materials 0.000 description 1
- 239000004962 Polyamide-imide Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
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- 239000012790 adhesive layer Substances 0.000 description 1
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- 229910045601 alloy Inorganic materials 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 150000001721 carbon Chemical group 0.000 description 1
- 229910021387 carbon allotrope Inorganic materials 0.000 description 1
- 150000004649 carbonic acid derivatives Chemical class 0.000 description 1
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- 210000001787 dendrite Anatomy 0.000 description 1
- 238000001739 density measurement Methods 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 239000011245 gel electrolyte Substances 0.000 description 1
- 229910021385 hard carbon Inorganic materials 0.000 description 1
- 238000005338 heat storage Methods 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 229910003437 indium oxide Inorganic materials 0.000 description 1
- PJXISJQVUVHSOJ-UHFFFAOYSA-N indium(iii) oxide Chemical compound [O-2].[O-2].[O-2].[In+3].[In+3] PJXISJQVUVHSOJ-UHFFFAOYSA-N 0.000 description 1
- 229910052745 lead Inorganic materials 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- FUJCRWPEOMXPAD-UHFFFAOYSA-N lithium oxide Chemical compound [Li+].[Li+].[O-2] FUJCRWPEOMXPAD-UHFFFAOYSA-N 0.000 description 1
- 229910001947 lithium oxide Inorganic materials 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical group [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 229910021382 natural graphite Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
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- 229910052697 platinum Inorganic materials 0.000 description 1
- 239000004584 polyacrylic acid Substances 0.000 description 1
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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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Cell Electrode Carriers And Collectors (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Description
本発明は、非水電解質二次電池に関する。より詳細には、電解質として水を含まない二次電池に関する。 The present invention relates to a non-aqueous electrolyte secondary battery. More specifically, the present invention relates to a secondary battery that does not contain water as an electrolyte.
二次電池は、いわゆる“蓄電池”ゆえに充電・放電の繰り返し可能であり、様々な用途に用いられている。例えば、携帯電話、スマートフォンおよびノートパソコンなどのモバイル機器に二次電池が用いられており、特にリチウムイオン電池に代表される非水電解質二次電池が多く用いられている。 The secondary battery can be repeatedly charged and discharged because it is a so-called “storage battery”, and is used in various applications. For example, secondary batteries are used in mobile devices such as mobile phones, smartphones, and notebook computers, and non-aqueous electrolyte secondary batteries represented by lithium ion batteries are particularly frequently used.
かかる非水電解質二次電池は、高エネルギー密度を有しながらも、繰り返しの充電・放電で劣化しにくいサイクル特性および高安全性などが一般に求められる。これにより、二次電池を使用するモバイル機器などの利便性が更に向上し、近年のニーズにより好適に対応できるようになる。 Such a non-aqueous electrolyte secondary battery is generally required to have cycle characteristics and high safety that are not easily deteriorated by repeated charging and discharging while having a high energy density. As a result, the convenience of a mobile device using a secondary battery is further improved, and it is possible to more appropriately cope with recent needs.
本願発明者は、所望の非水電解質二次電池を得るに際して克服すべき課題あることに気付き、そのための対策を取る必要性を見出した。具体的には以下の課題があることを本願発明者は見出した。 The inventor of the present application has found that there is a problem to be overcome when obtaining a desired non-aqueous electrolyte secondary battery, and has found that it is necessary to take measures for that purpose. Specifically, the present inventors have found that there are the following problems.
非水電解質二次電池において高エネルギー密度や小型化を達成するために、例えば正極の集電体を薄くすることが考えられる。 In order to achieve high energy density and miniaturization in a nonaqueous electrolyte secondary battery, for example, it is conceivable to make the current collector of the positive electrode thin.
しかしながら、集電体を薄くすると、放熱性が損なわれてしまい、熱が電池にこもる傾向がみられる。つまり、非水電解質二次電池において局所発熱が発生し易くなってしまう。その結果、電池のサイクル特性または安全性が悪化してしまう虞がある。 However, when the current collector is thinned, heat dissipation is impaired, and heat tends to be trapped in the battery. That is, local heat generation is likely to occur in the nonaqueous electrolyte secondary battery. As a result, the cycle characteristics or safety of the battery may be deteriorated.
本発明はかかる課題に鑑みて為されたものである。即ち、本発明の主たる目的は、局所発熱が好適に抑制された非水電解質二次電池を提供することである。 The present invention has been made in view of such problems. That is, the main object of the present invention is to provide a nonaqueous electrolyte secondary battery in which local heat generation is suitably suppressed.
本願発明者は、従来技術の延長線上で対応するのではなく、新たな方向で対処することによって上記課題の解決を試みた。その結果、上記主たる目的が達成された非水電解質二次電池の発明に至った。 The inventor of the present application tried to solve the above-mentioned problem by addressing in a new direction instead of responding on the extension of the prior art. As a result, the inventors have reached the invention of a non-aqueous electrolyte secondary battery in which the main object is achieved.
本発明に係る非水電解質二次電池は、
正極集電体の少なくとも片面に正極材層が設けられた正極、負極集電体の少なくとも片面に負極材層が設けられた負極、正極と負極との間に位置付けられたセパレータ、および、非水電解質とを有して成り、
正極材層に炭素繊維材を含んで成り、正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下であることを特徴とする。
Nonaqueous electrolyte secondary battery according to the present invention,
A positive electrode having a positive electrode material layer provided on at least one side of the positive electrode current collector, a negative electrode having a negative electrode material layer provided on at least one side of the negative electrode current collector, a separator positioned between the positive electrode and the negative electrode, and non-aqueous Comprising an electrolyte,
The positive electrode material layer includes a carbon fiber material, and the density of the positive electrode material layer is 3.85 g / cm 3 or more and 4.15 g / cm 3 or less.
本発明に係る非水電解質二次電池は、局所発熱が好適に抑制されている。つまり、本発明に係る非水電解質二次電池においては、集電体を薄くした場合であっても発熱が発生し難く、それゆえ、サイクル特性の低下が抑えられており、または、安全性がより改善されている。 In the nonaqueous electrolyte secondary battery according to the present invention, local heat generation is suitably suppressed. That is, in the non-aqueous electrolyte secondary battery according to the present invention, even when the current collector is thinned, heat generation is difficult to occur, and therefore deterioration in cycle characteristics is suppressed or safety is reduced. It has been improved.
以下では、本発明の一実施形態に係る非水電解質二次電池をより詳細に説明する。必要に応じて図面を参照して説明を行うものの、図面における各種の要素は、本発明の理解のために模式的かつ例示的に示したにすぎず、外観や寸法比などは実物と異なり得る。 Hereinafter, the nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described in more detail. Although the description will be made with reference to the drawings as necessary, the various elements in the drawings are merely schematically and exemplarily shown for the understanding of the present invention, and the appearance and size ratio may be different from the actual ones. .
本明細書において「非水電解質二次電池」といった用語は、充電・放電の繰り返しが可能な電池であって、電解質として有機電解質・有機溶媒などの“非水系”が用いられた電池のことを指している。特に、本発明における非水電解質二次電池では、セパレータを介して正極と負極とが積み重なった積層構造体に非水電解質が用いられている。 In this specification, the term “non-aqueous electrolyte secondary battery” refers to a battery that can be repeatedly charged and discharged, and uses a non-aqueous battery such as an organic electrolyte or an organic solvent as an electrolyte. pointing. In particular, in the nonaqueous electrolyte secondary battery according to the present invention, a nonaqueous electrolyte is used in a laminated structure in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween.
本明細書において説明される「密度」（具体的には“正極材層密度”）、含有量（具体的には“炭素繊維材の含有量”）ならびに「厚み」（具体的には例えば“正極集電体厚み”および“負極集電体厚み”）などの値は、“放電時”におけるものを実質的に指している。あくまでも例示にすぎないが、これらの値は、充電と放電とがなされる充放電を１サイクルとすると、製造した非水電解質二次電池について少なくとも１サイクル以上の充放電がなされた放電後（１つの指標として公称電圧の８０％の電圧となった放電状態）における値を実質的に意味している。なお、本明細書で直接的または間接的に説明される“厚み”の方向は、非水電解質二次電池を構成する電極材の積層方向に基づいており、即ち、“厚み”は正極と負極との積層方向における寸法に相当する。 “Density” (specifically “positive electrode material layer density”), content (specifically “content of carbon fiber material”) and “thickness” (specifically “ Values such as “positive electrode current collector thickness” and “negative electrode current collector thickness”) substantially refer to those at “during discharge”. These values are merely examples, but these values are assumed to be one cycle after charging / discharging (1) for the manufactured nonaqueous electrolyte secondary battery, assuming that charging / discharging is one cycle. As one index, it substantially means a value in a discharge state where the voltage becomes 80% of the nominal voltage. In addition, the direction of “thickness” described directly or indirectly in the present specification is based on the stacking direction of the electrode material constituting the nonaqueous electrolyte secondary battery, that is, “thickness” is the positive electrode and the negative electrode This corresponds to the dimension in the stacking direction.
［本発明の非水電解質二次電池の構成］
本発明に係る非水電解質二次電池は、正極、負極、セパレータおよび非水電解質から少なくとも構成されている。図１に示されるように、正極１と負極２とはセパレータ３を介して積層した構造を有しており、そのような積層構造体１００’が非水電解質と共に外装に封入されている。
[Configuration of Nonaqueous Electrolyte Secondary Battery of the Present Invention]
The nonaqueous electrolyte secondary battery according to the present invention includes at least a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. As shown in FIG. 1, the positive electrode 1 and the negative electrode 2 have a structure in which they are stacked via a separator 3, and such a stacked structure 100 ′ is enclosed in an exterior together with a nonaqueous electrolyte.
正極１は正極材層および正極集電箔から少なくとも構成されており、図１に示すように正極集電箔１０の少なくとも片面に正極材層１５が設けられている。正極材層１５には正極活物質が含まれている。同様に、負極２は負極材層および負極集電箔から少なくとも構成されており、図１に示すように負極集電箔２０の少なくとも片面に負極材層２５が設けられている。負極材層２５には負極活物質が含まれている。 The positive electrode 1 includes at least a positive electrode material layer and a positive electrode current collector foil, and a positive electrode material layer 15 is provided on at least one surface of the positive electrode current collector foil 10 as shown in FIG. The positive electrode material layer 15 contains a positive electrode active material. Similarly, the negative electrode 2 includes at least a negative electrode material layer and a negative electrode current collector foil, and a negative electrode material layer 25 is provided on at least one surface of the negative electrode current collector foil 20 as shown in FIG. The negative electrode material layer 25 contains a negative electrode active material.
正極活物質および負極活物質は、二次電池において電子の受け渡しに直接関与する物質であり、充放電、すなわち電池反応を担う正負極の主物質である。より具体的には、「正極材層に含まれる正極活物質」および「負極材層に含まれる負極活物質」に起因して非水電解質にイオンがもたらされ、かかるイオンが正極と負極との間で移動して電子の受け渡しが行われて充放電がなされる。後述でも触れるが、正極材層および負極材層は特にリチウムイオンを吸蔵放出可能な層であることが好ましい。つまり、非水電解質を介してリチウムイオンが正極と負極との間で移動して電池の充放電が行われる非水電解質二次電池となっていることが好ましい。充放電にリチウムイオンが関与する場合、本発明に係る非水電解質二次電池は、いわゆる“リチウムイオン電池”に相当する。また、本発明の１つの好適な実施態様では非水電解質二次電池の充電電圧は４．３５Ｖ以上である。 The positive electrode active material and the negative electrode active material are materials directly involved in the transfer of electrons in the secondary battery, and are the main materials of the positive and negative electrodes responsible for charge / discharge, that is, the battery reaction. More specifically, ions are brought into the non-aqueous electrolyte due to the “positive electrode active material contained in the positive electrode material layer” and the “negative electrode active material contained in the negative electrode material layer”, and these ions are Between the two, the electrons are transferred and charged and discharged. As will be described later, the positive electrode material layer and the negative electrode material layer are particularly preferably layers capable of occluding and releasing lithium ions. That is, it is preferable to be a nonaqueous electrolyte secondary battery in which lithium ions move between the positive electrode and the negative electrode through the nonaqueous electrolyte and the battery is charged and discharged. When lithium ions are involved in charge / discharge, the nonaqueous electrolyte secondary battery according to the present invention corresponds to a so-called “lithium ion battery”. Moreover, in one suitable embodiment of this invention, the charging voltage of a nonaqueous electrolyte secondary battery is 4.35V or more.
正極材層の正極活物質は例えば粒状体から成るところ、粒子同士の十分な接触と形状保持のためにバインダー（“結着材”とも称される）が正極材層に含まれていることが好ましい。更には、電池反応を推進する電子の伝達を円滑にするために導電助剤が正極材層に含まれていることも好ましい。同様にして、負極材層の負極活物質は例えば粒状体から成るところ、粒子同士の十分な接触と形状保持のためにバインダーが含まれることが好ましく、電池反応を推進する電子の伝達を円滑にするために導電助剤が負極材層に含まれていてもよい。このように、複数の成分が含有されて成る形態ゆえ、正極材層および負極材層はそれぞれ“正極合材層”および“負極合材層”などと称すこともできる。 The positive electrode active material of the positive electrode material layer is made of, for example, a granular material, and a binder (also referred to as a “binder”) is included in the positive electrode material layer for sufficient contact between the particles and shape retention. preferable. Furthermore, it is also preferable that a conductive additive is included in the positive electrode material layer in order to facilitate the transmission of electrons that promote the battery reaction. Similarly, the negative electrode active material of the negative electrode material layer is made of, for example, a granular material, and it is preferable that a binder is included for sufficient contact and shape retention between the particles, and smooth transmission of electrons that promote the battery reaction. In order to do so, a conductive aid may be included in the negative electrode material layer. Thus, because of the form in which a plurality of components are contained, the positive electrode material layer and the negative electrode material layer can also be referred to as “positive electrode composite material layer” and “negative electrode composite material layer”, respectively.
正極活物質は、リチウムイオンの吸蔵放出に資する物質であることが好ましい。かかる観点でいえば、正極活物質は例えばリチウム含有複合酸化物であることが好ましい。より具体的には、正極活物質は、リチウムと、コバルト、ニッケル、マンガンおよび鉄から成る群から選択される少なくとも１種の遷移金属とを含むリチウム遷移金属複合酸化物であることが好ましい。つまり、本発明に係る非水電解質二次電池の正極材層においては、そのようなリチウム遷移金属複合酸化物が正極活物質として好ましくは含まれている。例えば、正極活物質はコバルト酸リチウム、ニッケル酸リチウム、マンガン酸リチウム、リン酸鉄リチウム、または、それらの遷移金属の一部を別の金属で置き換えたものであってよい。このような正極活物質は、単独種として含まれてよいものの、二種以上が組み合わされて含まれていてもよい。本発明の１つの好適な実施態様では正極材層に含まれる正極活物質がコバルト酸リチウムとなっている。 The positive electrode active material is preferably a material that contributes to occlusion and release of lithium ions. From this point of view, the positive electrode active material is preferably, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material is preferably a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron. That is, in the positive electrode material layer of the nonaqueous electrolyte secondary battery according to the present invention, such a lithium transition metal composite oxide is preferably included as a positive electrode active material. For example, the positive electrode active material may be lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, or a part of those transition metals replaced with another metal. Although such a positive electrode active material may be included as a single species, two or more types may be included in combination. In one preferred embodiment of the present invention, the positive electrode active material contained in the positive electrode material layer is lithium cobalt oxide.
正極材層に含まれる得るバインダーとしては、特に制限されるわけではないが、ポリフッ化ビリニデン、ビリニデンフルオライド−ヘキサフルオロプロピレン共重合体、ビリニデンフルオライド−テトラフルオロチレン共重合体およびポリテトラフルオロチレンなどから成る群から選択される少なくとも１種を挙げることができる。本発明の１つの好適な実施態様では正極材層のバインダーがポリフッ化ビニリデンとなっている。正極材層に含まれる得る導電助剤としては、特に制限されるわけではないが、サーマルブラック、ファーネスブラック、チャンネルブラック、ケッチェンブラックおよびアセチレンブラック等のカーボンブラック、黒鉛、カーボンナノチューブや気相成長炭素繊維等の炭素繊維、銅、ニッケル、アルミニウムおよび銀等の金属粉末、ならびに、ポリフェニレン誘導体などから選択される少なくとも１種を挙げることができる。 Binders that can be included in the positive electrode material layer are not particularly limited, but include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and Mention may be made of at least one selected from the group consisting of polytetrafluoroethylene and the like. In one preferred embodiment of the present invention, the binder of the positive electrode material layer is polyvinylidene fluoride. The conductive auxiliary agent that can be included in the positive electrode material layer is not particularly limited, but carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black, graphite, carbon nanotube, and vapor phase growth. Examples thereof include at least one selected from carbon fibers such as carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives.
負極活物質は、リチウムイオンの吸蔵放出に資する物質であることが好ましい。かかる観点でいえば、負極活物質は例えば各種の炭素材料、酸化物、または、リチウム合金などであることが好ましい。 The negative electrode active material is preferably a material that contributes to occlusion and release of lithium ions. From this point of view, the negative electrode active material is preferably, for example, various carbon materials, oxides, or lithium alloys.
負極活物質の各種の炭素材料としては、黒鉛（天然黒鉛、人造黒鉛）、ハードカーボン、ソフトカーボン、ダイヤモンド状炭素などを挙げることができる。特に、黒鉛は電子伝導性が高く、負極集電体との接着性が優れる点などで好ましい。負極活物質の酸化物としては、酸化シリコン、酸化スズ、酸化インジウム、酸化亜鉛および酸化リチウムなどから成る群から選択される少なくとも１種を挙げることができる。負極活物質のリチウム合金は、リチウムと合金形成され得る金属であればよく、例えば、Ａｌ、Ｓｉ、Ｐｂ、Ｓｎ、Ｉｎ、Ｂｉ、Ａｇ、Ｂａ、Ｃａ、Ｈｇ、Ｐｄ、Ｐｔ、Ｔｅ、Ｚｎ、Ｌａなどの金属とリチウムとの２元、３元またはそれ以上の合金であってよい。このような酸化物は、その構造形態としてアモルファスとなっていることが好ましい。結晶粒界または欠陥といった不均一性に起因する劣化が引き起こされにくくなるからである。本発明に係る非水電解質二次電池の１つの好適な実施態様では負極材層の負極活物質が人造黒鉛となっている。 Examples of various carbon materials of the negative electrode active material include graphite (natural graphite, artificial graphite), hard carbon, soft carbon, diamond-like carbon, and the like. In particular, graphite is preferable in that it has high electron conductivity and excellent adhesion to the negative electrode current collector. Examples of the oxide of the negative electrode active material include at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, and the like. The lithium alloy of the negative electrode active material may be any metal that can be alloyed with lithium. For example, Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, It may be a binary, ternary or higher alloy of a metal such as La and lithium. Such an oxide is preferably amorphous in its structural form. This is because deterioration due to non-uniformity such as crystal grain boundaries or defects is less likely to be caused. In one preferred embodiment of the nonaqueous electrolyte secondary battery according to the present invention, the negative electrode active material of the negative electrode material layer is artificial graphite.
負極材層に含まれる得るバインダーとしては、特に制限されるわけではないが、スチレンブタジエンゴム、ポリアクリル酸、ポリフッ化ビニリデン、ポリイミド系樹脂およびポリアミドイミド系樹脂から成る群から選択される少なくとも１種を挙げることができる。本発明の１つの好適な実施態様では負極材層に含まれるバインダーがスチレンブタジエンゴムとなっている。負極材層に含まれる得る導電助剤としては、特に制限されるわけではないが、サーマルブラック、ファーネスブラック、チャンネルブラック、ケッチェンブラックおよびアセチレンブラック等のカーボンブラック、黒鉛、カーボンナノチューブや気相成長炭素繊維等の炭素繊維、銅、ニッケル、アルミニウムおよび銀等の金属粉末、ならびに、ポリフェニレン誘導体などから選択される少なくとも１種を挙げることができる。なお、負極材層には、電池製造時に使用された増粘剤成分（例えばカルボキシルメチルセルロース）に起因する成分が含まれていてもよい。 The binder that can be included in the negative electrode material layer is not particularly limited, but is at least one selected from the group consisting of styrene butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resin, and polyamideimide resin. Can be mentioned. In one preferred embodiment of the present invention, the binder contained in the negative electrode material layer is styrene butadiene rubber. The conductive auxiliary agent that can be included in the negative electrode material layer is not particularly limited, but carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black, graphite, carbon nanotube, and vapor phase growth. Examples thereof include at least one selected from carbon fibers such as carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives. In addition, the component resulting from the thickener component (for example, carboxymethylcellulose) used at the time of battery manufacture may be contained in the negative electrode material layer.
本発明に係る非水電解質二次電池のより好適な実施態様では、負極材層における負極活物質およびバインダーが人造黒鉛とスチレンブタジエンゴムとの組合せとなっている。 In a more preferred embodiment of the nonaqueous electrolyte secondary battery according to the present invention, the negative electrode active material and the binder in the negative electrode material layer are a combination of artificial graphite and styrene butadiene rubber.
正極および負極に用いられる正極集電体および負極集電体は、電池反応に起因して活物質で発生した電子を集めたり供給したりするのに資する部材である。このような集電体は、シート状の金属部材であってよく、多孔または穿孔の形態を有していてよい。例えば、集電体は金属箔、パンチングメタル、網またはエキスパンドメタル等であってよい。正極に用いられる正極集電体は、アルミニウム、ステンレスおよびニッケル等から成る群から選択される少なくとも１種を含んだ金属箔から成るものが好ましく、例えばアルミニウム箔であってよい。一方、負極に用いられる負極集電体は、銅、ステンレスおよびニッケル等から成る群から選択される少なくとも１種を含んだ金属箔から成るものが好ましく、例えば銅箔であってよい。 The positive electrode current collector and the negative electrode current collector used for the positive electrode and the negative electrode are members that contribute to collecting and supplying electrons generated in the active material due to the battery reaction. Such a current collector may be a sheet-like metal member and may have a porous or perforated form. For example, the current collector may be a metal foil, a punching metal, a net or an expanded metal. The positive electrode current collector used for the positive electrode is preferably made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel and the like, and may be, for example, an aluminum foil. On the other hand, the negative electrode current collector used for the negative electrode is preferably made of a metal foil containing at least one selected from the group consisting of copper, stainless steel, nickel and the like, and may be, for example, a copper foil.
正極および負極のそれぞれにおいては、集電体の少なくとも片面に電極材層が設けられている。図１に示すように、正極１では正極集電体１０の少なくとも片面に正極材層１５が設けられている。好ましくは、正極集電体１０の両面に正極材層１５が設けられている。“両面”の場合、正極集電体１０は２つの正極材層１５に挟まれた形態を有している。同様にして、図１に示すように、負極２では負極集電体２０の少なくとも片面に負極材層２５が設けられている。好ましくは、負極集電体２０の両面に負極材層２５が設けられている。“両面”の場合、負極集電体２０は２つの負極材層２５に挟まれた形態を有している。 In each of the positive electrode and the negative electrode, an electrode material layer is provided on at least one surface of the current collector. As shown in FIG. 1, in the positive electrode 1, a positive electrode material layer 15 is provided on at least one surface of a positive electrode current collector 10. Preferably, the positive electrode material layer 15 is provided on both surfaces of the positive electrode current collector 10. In the case of “double-sided”, the positive electrode current collector 10 has a form sandwiched between two positive electrode material layers 15. Similarly, as shown in FIG. 1, in the negative electrode 2, a negative electrode material layer 25 is provided on at least one surface of the negative electrode current collector 20. Preferably, the negative electrode material layer 25 is provided on both surfaces of the negative electrode current collector 20. In the case of “both sides”, the negative electrode current collector 20 has a form sandwiched between two negative electrode material layers 25.
このような正極１および負極２はセパレータ３を介して積層した形態を有している（図１参照）。セパレータは、正負極の接触による短絡防止および非水電解質保持などの観点から設けられる部材である。換言すれば、セパレータは、正極と負極と間の電子的接触を防止しつつイオンを通過させる部材であるといえる。好ましくは、セパレータは多孔性または微多孔性の絶縁性部材であり、その小さい厚みに起因して膜形態を有している。あくまでも例示にすぎないが、ポリオレフィン製の微多孔膜がセパレータとして用いられてよい。この点、セパレータとして用いられる微多孔膜は、例えば、ポリオレフィンとしてポリエチレン（ＰＥ）のみ又はポリエチレン（ＰＰ）のみを含んだものであってよい。更にいえば、セパレータは、“ＰＥ製の微多孔膜”と“ＰＰ製の微多孔膜”とから構成される積層体であってもよい。セパレータの表面が無機粒子コート層や接着層等により覆われていてもよい。セパレータの表面が接着性を有していてもよい。なお、本発明において、セパレータは、その名称によって特に拘泥されるべきでなく、同様の機能を有する固体電解質、ゲル状電解質、絶縁性の無機粒子などであってもよい。 Such a positive electrode 1 and a negative electrode 2 have the form laminated | stacked through the separator 3 (refer FIG. 1). The separator is a member provided from the viewpoints of preventing short circuit due to contact between the positive and negative electrodes and holding the nonaqueous electrolyte. In other words, the separator can be said to be a member that allows ions to pass while preventing electronic contact between the positive electrode and the negative electrode. Preferably, the separator is a porous or microporous insulating member and has a film form due to its small thickness. Although only illustrative, a polyolefin microporous film may be used as the separator. In this regard, the microporous film used as the separator may include, for example, only polyethylene (PE) or only polyethylene (PP) as the polyolefin. Furthermore, the separator may be a laminate composed of “a microporous membrane made of PE” and “a microporous membrane made of PP”. The surface of the separator may be covered with an inorganic particle coat layer, an adhesive layer, or the like. The surface of the separator may have adhesiveness. In the present invention, the separator is not particularly limited by its name, and may be a solid electrolyte, a gel electrolyte, insulating inorganic particles or the like having the same function.
本発明の非水電解質二次電池では、セパレータを介して構成された正極・負極の積層構造体が非水電解質と共に外装に封入されている。非水電解質は、有機電解質・有機溶媒などの“非水系”の溶媒と、溶質とを含む電解質である。かかる電解質においては電極（正極・負極）から放出された金属イオンが存在することになり、それゆえ、電解質は電池反応における金属イオンの移動を助力する。本発明における非水電解質は液体状またはゲル状などの形態を有し得る（なお、本明細書において“液体状”の非水電解質は「非水電解質液」とも称される）。 In the non-aqueous electrolyte secondary battery of the present invention, a laminated structure of positive and negative electrodes configured via a separator is enclosed in an exterior together with the non-aqueous electrolyte. The non-aqueous electrolyte is an electrolyte containing a “non-aqueous” solvent such as an organic electrolyte / organic solvent and a solute. In such an electrolyte, metal ions released from the electrodes (positive electrode / negative electrode) exist, and therefore the electrolyte assists the movement of metal ions in the battery reaction. The nonaqueous electrolyte in the present invention may have a form such as liquid or gel (in the present specification, the “liquid” nonaqueous electrolyte is also referred to as “nonaqueous electrolyte solution”).
具体的な非水電解質の溶媒としては、少なくともカーボネートを含んで成るものが好ましい。かかるカーボネートは、環状カーボネート類および／または鎖状カーボネート類であってもよい。特に制限されるわけではないが、環状カーボネート類としては、プロピレンカーボネート（ＰＣ）、エチレンカーボネート（ＥＣ）、ブチレンカーボネート（ＢＣ）およびビニレンカーボネート（ＶＣ）から成る群から選択される少なくとも１種を挙げることができる。鎖状カーボネート類としては、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）およびジプロピルカーボネート（ＤＰＣ）から成る群から選択される少なくも１種を挙げることができる。本発明の１つの好適な実施態様では、非水電解質として環状カーボネート類と鎖状カーボネート類との組合せが用いられ、例えばエチレンカーボネートとジエチルカーボネートとの混合物が用いられる。
具体的な非水電解質の溶質としては、例えば、ＬｉＰＦ６および／またはＬｉＢＦ４などのＬｉ塩が好ましく用いられる。
As a specific non-aqueous electrolyte solvent, a solvent containing at least carbonate is preferable. Such carbonates may be cyclic carbonates and / or chain carbonates. Although not particularly limited, examples of the cyclic carbonates include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC). be able to. Examples of the chain carbonates include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dipropyl carbonate (DPC). In one preferred embodiment of the present invention, a combination of cyclic carbonates and chain carbonates is used as the non-aqueous electrolyte, for example, a mixture of ethylene carbonate and diethyl carbonate.
As a specific nonaqueous electrolyte solute, for example, a Li salt such as LiPF 6 and / or LiBF 4 is preferably used.
［本発明の非水電解質二次電池の特徴］
本発明の非水電解質二次電池は正極材層の構成材および密度の点で少なくとも特徴を有している。具体的には、正極材層に炭素繊維材が含まれていると共に、正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下となっている。図１に示すように、炭素繊維材５０は、あくまでも“繊維”状であり、全体形状が細長くなっており、そのような“繊維”が正極材層に全体的に分散した状態となっていることが好ましい。このように本発明の非水電解質二次電池では正極材層が炭素繊維材５０を含んで成り、かかる炭素繊維材５０を含んだ正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下となっている。
[Features of Nonaqueous Electrolyte Secondary Battery of the Present Invention]
The nonaqueous electrolyte secondary battery of the present invention has at least characteristics in terms of the constituent material and density of the positive electrode material layer. Specifically, a carbon fiber material is included in the positive electrode material layer, and the density of the positive electrode material layer is 3.85 g / cm 3 or more and 4.15 g / cm 3 or less. As shown in FIG. 1, the carbon fiber material 50 is in the form of “fiber” to the last, the entire shape is elongated, and such “fiber” is dispersed in the positive electrode material layer as a whole. It is preferable. Thus, in the non-aqueous electrolyte secondary battery of the present invention, the positive electrode material layer includes the carbon fiber material 50, and the density of the positive electrode material layer including the carbon fiber material 50 is 3.85 g / cm 3 or more and 4.15 g. / Cm 3 or less.
正極材層に炭素繊維材が含まれると共に、正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下となる場合、非水電解質二次電池の局所発熱が好適に抑制され得ることになる。そのような発熱の抑制は、電池の熱暴走が抑えられること意味しており、それゆえ、本発明の１つの好適な実施形態に係る非水電解質二次電池は、サイクル特性の低下が抑えられ得ると共に、安全性がより改善され得る。 When the carbon material is included in the positive electrode material layer and the density of the positive electrode material layer is 3.85 g / cm 3 or more and 4.15 g / cm 3 or less, local heat generation of the nonaqueous electrolyte secondary battery is suitably suppressed. Will get. Such suppression of heat generation means that thermal runaway of the battery is suppressed. Therefore, the non-aqueous electrolyte secondary battery according to one preferred embodiment of the present invention can suppress deterioration of cycle characteristics. And safety can be further improved.
本発明は、正極集電体を薄くした場合に特に有用な効果がもたらされる。なぜなら、非水電解質二次電池の高エネルギー密度や小型化の観点で正極集電体を薄くすると、“局所発熱”が発生し易い傾向が出てくるからである。具体的には、正極集電箔を薄くすると、サイクル特性や釘刺し安全性が悪化し得る。特定の理論に拘束されるわけではないが、これは、正極の熱伝導性の低下が要因と考えられる。サイクル特性の悪化は蓄熱による正極の劣化につながり得、また、安全性の悪化は正極活物質の熱分解による電池の熱暴走につながり得る。この点、本発明の非水電解質二次電池では、正極集電体が薄い場合であっても、そのような不都合が抑制され得る。 The present invention provides a particularly useful effect when the positive electrode current collector is thinned. This is because if the positive electrode current collector is thinned from the viewpoint of high energy density and miniaturization of the nonaqueous electrolyte secondary battery, “local heat generation” tends to occur. Specifically, when the positive electrode current collector foil is thinned, cycle characteristics and nail penetration safety may be deteriorated. Although not bound by a specific theory, this is considered to be caused by a decrease in the thermal conductivity of the positive electrode. Deterioration of cycle characteristics can lead to deterioration of the positive electrode due to heat storage, and deterioration of safety can lead to thermal runaway of the battery due to thermal decomposition of the positive electrode active material. In this regard, in the nonaqueous electrolyte secondary battery of the present invention, such inconvenience can be suppressed even when the positive electrode current collector is thin.
例えば、本発明の１つの好適な実施形態に係る非水電解質二次電池では、正極集電体の厚みが小さい場合であっても、本発明の非水電解質二次電池は、“炭素繊維材の含有および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層”に起因して局所発熱が抑制されており、それゆえ、サイクル特性の低下が好適に抑えられ得、および／または、安全性がより改善され得る。正極集電体の薄い厚みは、好ましくは１２μｍ以下、より好ましくは１１μｍ以下（例えば、１０μｍ以下）である。かかる場合、正極集電体は金属箔（例えばアルミニウム箔）であってよく、かかる金属箔が好ましくは１２μｍ以下、より好ましくは１１μｍ以下（例えば、１０μｍ以下）となっていてよい。なお、正極集電体の厚みの下限値は、集電体としての機能および／または構造強度を損なわないものであれば特に制限はなく、例えば２μｍ以上４μｍ以下程度（例えば３μｍ）であってよい。 For example, in the non-aqueous electrolyte secondary battery according to one preferred embodiment of the present invention, the non-aqueous electrolyte secondary battery of the present invention is “carbon fiber material” even when the thickness of the positive electrode current collector is small. Content and a positive electrode material layer having a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less ”, local heat generation is suppressed, and therefore, deterioration of cycle characteristics can be suitably suppressed, and Or, safety can be further improved. The thin thickness of the positive electrode current collector is preferably 12 μm or less, more preferably 11 μm or less (for example, 10 μm or less). In such a case, the positive electrode current collector may be a metal foil (for example, an aluminum foil), and the metal foil may be preferably 12 μm or less, more preferably 11 μm or less (for example, 10 μm or less). The lower limit of the thickness of the positive electrode current collector is not particularly limited as long as it does not impair the function and / or structural strength of the current collector, and may be, for example, about 2 μm to 4 μm (for example, 3 μm). .
このように本発明では炭素繊維材の含有および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層が非水電解質二次電池の発熱の抑制に特に有利に寄与する。特定の理論に拘束されるわけではないが、これは、正極の熱伝導性が高くなり、かつ、正極材層から正極集電体または電解液への熱移動がスムーズに行われることが要因として考えられる。正極材層の密度が３．８５ｇ／ｃｍ３未満の場合、正極材層を構成する粒状物質同士の密着性が低下するので、正極の熱伝導性が悪くなり、サイクル特性や安全性が悪くなるものと推測される。一方、正極材層の密度が４．１５ｇ／ｃｍ３よりも大きくなると、正極材層内へと非水電解質が入る空隙が小さくなり、電解液が含浸した状態の正極の比熱が低くなってしまうので、局所的に熱が発生しやすくなり、サイクル特性や安全性が悪くなるものと推測される。 Thus, in the present invention, the inclusion of the carbon fiber material and the positive electrode material layer having a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less contribute particularly advantageously to suppression of heat generation of the nonaqueous electrolyte secondary battery. While not being bound by any particular theory, this is because the positive electrode has higher thermal conductivity and smooth heat transfer from the positive electrode material layer to the positive electrode current collector or electrolyte. Conceivable. When the density of the positive electrode material layer is less than 3.85 g / cm 3, the adhesiveness between the particulate materials constituting the positive electrode material layer is lowered, so that the thermal conductivity of the positive electrode is deteriorated and the cycle characteristics and safety are deteriorated. Presumed to be. On the other hand, when the density of the positive electrode material layer is larger than 4.15 g / cm 3 , the gap into which the non-aqueous electrolyte enters the positive electrode material layer is reduced, and the specific heat of the positive electrode impregnated with the electrolytic solution is lowered. Therefore, it is presumed that heat is likely to be generated locally, and cycle characteristics and safety are deteriorated.
なお、本明細書における「密度」は、正極材層の厚さ寸法および電極作製時の正極材層原料の使用量から算出したものであってよい。具体的には、例えば以下の測定手法で得られた密度値を本発明における“密度”（正極材層の密度）としてよい。
・密度測定：放電状態の非水電解質二次電池をアルゴン雰囲気下のグローブボックス内で解体し、正極を取り出す。そのようにして取り出された正極についてデジタルマイクロメーター（ミツトヨ製ＭＤＨ−２５Ｍ）で厚み測定を行う。得られた厚み（μｍ）と、「電極作製時に正極集電体上に塗布された正極材原料の塗布量（ｍｇ／ｃｍ２）」を用いて正極材層の密度を算出する。
The “density” in the present specification may be calculated from the thickness dimension of the positive electrode material layer and the amount of the positive electrode material layer raw material used at the time of electrode preparation. Specifically, for example, the density value obtained by the following measurement method may be used as the “density” in the present invention (the density of the positive electrode material layer).
Density measurement : Discharged nonaqueous electrolyte secondary battery is disassembled in a glove box under an argon atmosphere, and the positive electrode is taken out. The thickness of the positive electrode thus taken out is measured with a digital micrometer (Mitutoyo MDH-25M). The density of the positive electrode material layer is calculated using the obtained thickness (μm) and “the applied amount (mg / cm 2 ) of the positive electrode material raw material applied on the positive electrode current collector during electrode production”.
本発明の非水電解質二次電池では正極材層に含まれる炭素繊維材は、あまり多くなくてよい。例えば、炭素繊維材の含有量が正極材層の全体基準で０．５重量％以上となっており、好ましくは０．５重量％以上１０重量％以下程度、より好ましくは０．５重量％以上５重量％以下程度、更に好ましくは０．５重量％以上１．５重量％以下程度である。このような少ない炭素繊維材の含有量であっても、本発明の非水電解質二次電池では正極の熱伝導性、放熱性、さらには導電性などが向上することになり、その結果、不都合な“局所発熱”が抑制されることになる。 In the nonaqueous electrolyte secondary battery of the present invention, the carbon fiber material contained in the positive electrode material layer may not be so much. For example, the content of the carbon fiber material is 0.5% by weight or more based on the entire positive electrode material layer, preferably about 0.5% by weight to 10% by weight, more preferably 0.5% by weight or more. It is about 5% by weight or less, more preferably about 0.5% by weight or more and 1.5% by weight or less. Even with such a small amount of carbon fiber material, the non-aqueous electrolyte secondary battery of the present invention improves the thermal conductivity, heat dissipation, and conductivity of the positive electrode. "Local heat generation" is suppressed.
本発明の１つの好適な実施形態に係る非水電解質二次電池では、炭素繊維材はカーボンナノチューブとなっている。カーボンナノチューブは、六角網目状の炭素原子配列のグラフアイトシートが円筒状に巻かれた構造を有する炭素同素体の１つであり、その直径がナノメートルのオーダーを有している。カーボンナノチューブの種類としては、単層カーボンナノチューブおよび多層カーボンナノチューブがある。単層カーボンナノチューブは、グラフアイトシートが一枚だけ円筒状に巻かれたものであるのに対して、多層カーボンナノチューブは、グラフアイトシートが同心円状に略等間隔に何重にも重なったものである。本発明で正極材層に含まれる炭素繊維材としてのカーボンナノチューブは、単層カーボンナノチューブ、多層カーボンナノチューブ、または、これらの混合物であってよい。 In the nonaqueous electrolyte secondary battery according to one preferred embodiment of the present invention, the carbon fiber material is a carbon nanotube. The carbon nanotube is one of carbon allotropes having a structure in which a hexagonal-shaped carbon atom array graphite sheet is wound in a cylindrical shape, and has a diameter in the order of nanometers. The types of carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled carbon nanotubes are made by winding only one graphite sheet in a cylindrical shape, whereas multi-walled carbon nanotubes are made by overlapping multiple graphite sheets at almost equal intervals in a concentric manner It is. In the present invention, the carbon nanotube as the carbon fiber material contained in the positive electrode material layer may be a single-walled carbon nanotube, a multi-walled carbon nanotube, or a mixture thereof.
カーボンナノチューブの直径について例示しておく。正極材層に含まれる炭素繊維材としてのカーボンナノチューブは、その直径が、好ましくは２ｎｍ以上１５ｎｍ以下、より好ましくは５ｎｍ以上１２ｎｍ以下となっている。また、カーボンナノチューブが炭素繊維材として用いられる場合、かかるカーボンナノチューブ自体が好適な伝導性を有しているので、カーボンブラックなどの導電助剤が正極材層に含まれていなくてよい。 The diameter of the carbon nanotube will be exemplified. The carbon nanotube as the carbon fiber material contained in the positive electrode material layer has a diameter of preferably 2 nm to 15 nm, more preferably 5 nm to 12 nm. In addition, when carbon nanotubes are used as the carbon fiber material, the carbon nanotubes themselves have suitable conductivity, so that a conductive aid such as carbon black may not be included in the positive electrode material layer.
あくまでも一例にすぎないが、炭素繊維材の含有（例えば、０．５重量％以上の含有）および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層を備えた非水電解質二次電池は、２５℃温度条件下の充放電サイクル５００回後の容量維持率が８９％以上（例えば、８９％以上９４％以下）となり得るのに対して、そのような条件にない正極材層を備えた非水電解質二次電池は、２５℃温度条件下で充放電サイクル５００回後の容量維持率が８９％未満（例えば、７１％以上８４％以下）となり得る。「７１％〜８４％」（平均７７．５％）から「８９％〜９４％」（平均９１．５％）へと増加することに鑑みれば、本発明に係る非水電解質二次電池では容量維持率が１．８割程度向上し得るといえる。 Although it is only an example to the last, the non-aqueous electrolyte provided with the positive electrode material layer containing carbon fiber material (for example, containing 0.5% by weight or more) and having a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less In the secondary battery, the capacity retention rate after 500 charge / discharge cycles at 25 ° C. can be 89% or more (for example, 89% or more and 94% or less), whereas the positive electrode material which does not satisfy such conditions A non-aqueous electrolyte secondary battery including a layer can have a capacity retention rate of less than 89% (for example, 71% or more and 84% or less) after 500 charge / discharge cycles under a temperature condition of 25 ° C. In view of the increase from “71% to 84%” (average 77.5%) to “89% to 94%” (average 91.5%), the non-aqueous electrolyte secondary battery according to the present invention has a capacity. It can be said that the maintenance rate can be improved by about 1.8%.
なお、本明細書にいう「２５℃温度条件下の充放電サイクル５００回後の容量維持率」とは、以下の“１サイクル”に基づいて、２５℃の恒温槽環境下で充電（“定電流定電圧充電”）と放電とを繰り返し行うことを前提条件とした５００サイクル後の容量維持率（％）を示している。
・１サイクル：作製した非水電解質二次電池につき、１Ｃの電流値で電圧４．３５Ｖまで定電流充電を行った後、電圧４．３５Ｖで１時間の定電圧充電を行う充電と、かかる充電後に１０分の休止時間を取ってから１Ｃの電流値で電圧３．０Ｖまで定電流放電を行う放電との組合せを１サイクルとする（なお、サイクル間では１０分の休止時間を取る）
・容量維持率（％）：（５００サイクル目の放電容量／１サイクル目の放電容量）×１００
The “capacity maintenance rate after 500 charge / discharge cycles under 25 ° C. temperature condition” in this specification is based on the following “one cycle” and is charged in a constant temperature bath environment at 25 ° C. The capacity retention rate (%) after 500 cycles is shown on the precondition that the current constant voltage charging ") and discharging are repeated.
-1 cycle : after the constant current charge to the voltage 4.35V with the electric current value of 1C about the produced nonaqueous electrolyte secondary battery, the charge which performs the constant voltage charge for 1 hour with the voltage 4.35V, and this charge A combination of a discharge with constant current discharge to a voltage of 3.0 V at a current value of 1 C after taking a pause time of 10 minutes later is defined as one cycle (note that a pause time of 10 minutes is taken between cycles).
Capacity retention rate (%) : (discharge capacity at 500th cycle / discharge capacity at the first cycle) × 100
また、同様にあくまでも一例にすぎないが、炭素繊維材の含有（例えば、０．５重量％以上の含有）および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層を備えた非水電解質二次電池は、以下の安全性試験において発火が生じないのに対して、そのような条件にない正極材層を備えた非水電解質二次電池は、発火が生じ得る。
・安全性試験：作製した非水電解質二次電池につき、１Ｃの電流値で電圧４．３５Ｖまで定電流充電を行った後、電圧４．３５Ｖで１時間の定電圧充電を行って満充電状態にする。次いで、満充電状態の電池の中心部分に直径３ｍｍの鉄製の釘を１００ｍｍ／ｍｉｎの速度で刺して発火の有無（発火有：ＮＧ、発火無：Ｇ）を評価する。なお、付加的には、釘を刺した直後から１２０秒後までの電池表面の温度を電池表面に取り付けた熱電対で測定し、温度測定中における電池表面の最高温度を確認する。
Similarly, although it is merely an example, it includes a positive electrode material layer having a carbon fiber material content (for example, 0.5% by weight or more) and a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less. The non-aqueous electrolyte secondary battery does not ignite in the following safety test, whereas the non-aqueous electrolyte secondary battery including the positive electrode material layer not in such a condition can ignite.
・Safety test : The manufactured nonaqueous electrolyte secondary battery was charged at a constant current up to a voltage of 4.35 V at a current value of 1 C, and then charged at a voltage of 4.35 V for 1 hour to be fully charged. To. Next, an iron nail having a diameter of 3 mm is pierced into the center portion of the fully charged battery at a speed of 100 mm / min to evaluate the presence or absence of ignition (ignition: NG, no ignition: G). In addition, the temperature of the battery surface from 120 seconds after the nail is stabbed is measured with a thermocouple attached to the battery surface, and the maximum temperature of the battery surface during temperature measurement is confirmed.
上記の安全性試験において、炭素繊維材の含有（例えば、０．５重量％以上の含有）および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層を備えた非水電解質二次電池の表面最高温度が１０５℃以上１３２℃以下となり得るのに対して、そのような条件にない正極材層を備えた非水電解質二次電池の表面最高温度が４２４℃以上５２１℃以下となり得る。 In the safety test, a non-aqueous electrolyte provided with a positive electrode material layer having a carbon fiber material content (for example, 0.5% by weight or more) and a density of 3.85 g / cm 3 to 4.15 g / cm 3 The maximum surface temperature of the secondary battery can be 105 ° C. or more and 132 ° C. or less, whereas the maximum surface temperature of the nonaqueous electrolyte secondary battery including the positive electrode material layer that does not satisfy such conditions is 424 ° C. or more and 521 ° C. or less. Can be.
本発明の１つの好適な実施態様に係る非水電解質二次電池は、その充電電圧が４．３５Ｖ以上であり、および／または、負極の正極と対向する部分における可逆容量の割合を示すＮ／Ｐ比が１．０５以下となっている。充電電圧が４．３５Ｖ以上の場合、例えば、４．３５Ｖ以上４．４５Ｖ以下などは従前の充電電圧よりも高く、いわゆる“次世代”の位置付けに相当する充電電圧となっている。このような高い充電電圧は電池容量が増すので高エネルギー密度を達成するうえで好ましい。また、「Ｎ／Ｐ比」は、本明細書では非水電解質二次電池の定格容量（Ｎ、ｍＡｈ）に対する負極の正極と対向する部分における可逆容量（Ｐ、ｍＡｈ）の割合を示すものであり、本発明の非水電解質二次電池ではそれが好ましくは１．０５以下（１＜Ｎ／Ｐ比≦１．０５）となっている。なお、Ｐの値は非水電解質二次電池に用いられる負極の単位面積当たりの可逆容量（ｍＡｈ／ｃｍ２）と非水電解質二次電池における正極と負極の対向部分の面積（ｃｍ２）との積から求めることができる。負極の単位面積当たりの可逆容量は、例えば、非水電解質二次電池の解体により取り出した負極を用いて、対極をリチウム、作用極を負極とした電池の定電流充放電測定を行うことで得ることができる。正極と負極の対向部分の面積は、例えば、非水電解質二次電池の解体時に正極の寸法を測定することにより算出することができる。Ｎ／Ｐ比の値は、このようにして得られたＮの値とＰの値から得ることができる。“１．０５以下のＮ／Ｐ比”は、電池内の負極活物質のうちで無駄となる部分がより少なく高エネルギー密度を達成するうえで好ましい。しかしながら、“１．０５以下のＮ／Ｐ比”は、一般的にはデンドライトが析出し易くなるので、繰り返される充電・放電に伴う容量低下を促進することなり、過充電に起因した発熱・発火を引き起こしやすかったりする。この点、本発明では、そのような不都合を引き起こしやすいと考えられる条件でありながらも、それらをより抑制した状態で高い容量維持率を達成することができる。 The nonaqueous electrolyte secondary battery according to one preferred embodiment of the present invention has a charging voltage of 4.35 V or more and / or N / which indicates a ratio of reversible capacity in a portion of the negative electrode facing the positive electrode. The P ratio is 1.05 or less. When the charging voltage is 4.35 V or higher, for example, 4.35 V or higher and 4.45 V or lower is higher than the conventional charging voltage, which corresponds to the so-called “next generation” positioning. Such a high charging voltage is preferable for achieving a high energy density because the battery capacity increases. In addition, the “N / P ratio” in this specification indicates the ratio of the reversible capacity (P, mAh) at the portion facing the positive electrode of the negative electrode to the rated capacity (N, mAh) of the nonaqueous electrolyte secondary battery. In the non-aqueous electrolyte secondary battery of the present invention, it is preferably 1.05 or less (1 <N / P ratio ≦ 1.05). Note that the value of P is the reversible capacity per unit area (mAh / cm 2 ) of the negative electrode used in the nonaqueous electrolyte secondary battery, and the area (cm 2 ) of the opposing portion of the positive electrode and negative electrode in the nonaqueous electrolyte secondary battery. It can be calculated from the product of The reversible capacity per unit area of the negative electrode is obtained, for example, by performing a constant current charge / discharge measurement of the battery using the negative electrode taken out by disassembly of the nonaqueous electrolyte secondary battery and using the counter electrode as lithium and the working electrode as the negative electrode. be able to. The area of the opposing part of the positive electrode and the negative electrode can be calculated, for example, by measuring the dimensions of the positive electrode when the nonaqueous electrolyte secondary battery is disassembled. The value of the N / P ratio can be obtained from the values of N and P thus obtained. The “N / P ratio of 1.05 or less” is preferable for achieving a high energy density with fewer wasted portions of the negative electrode active material in the battery. However, “N / P ratio of 1.05 or less” generally facilitates the precipitation of dendrites, which promotes a decrease in capacity due to repeated charge / discharge, and generates heat / ignition caused by overcharge. It is easy to cause. In this respect, the present invention can achieve a high capacity retention rate in a state in which they are further suppressed, although the conditions are likely to cause such inconvenience.
なお、“充電電圧４．３５Ｖ以上”および／または“Ｎ／Ｐ比１．０５以下”の非水電解質二次電池は、従来の当業者の認識からいえば、所望の高エネルギー密度を達成でき得る可能性はあるものの、安全性および／またはサイクル特性などが損なわれる虞がある。本発明に係る非水電解質二次電池は、そのように“充電電圧４．３５Ｖ以上”および／または“Ｎ／Ｐ比１．０５以下”であったとしても、安全性および／またはサイクル特性などを実質的に損なわず、高エネルギー密度が達成され得る。より具体的には、“充電電圧４．３５Ｖ以上”および／または“Ｎ／Ｐ比１．０５以下”の本発明に係る非水電解質二次電池では、上述の如く「２５℃温度条件下の充放電サイクル５００回後の容量維持率」が９０％以上となり得る。 A non-aqueous electrolyte secondary battery having a “charging voltage of 4.35 V or more” and / or “N / P ratio of 1.05 or less” can achieve a desired high energy density according to the knowledge of those skilled in the art. Although there is a possibility of being obtained, safety and / or cycle characteristics may be impaired. Even if the non-aqueous electrolyte secondary battery according to the present invention has a “charging voltage of 4.35 V or more” and / or “N / P ratio of 1.05 or less”, safety and / or cycle characteristics, etc. High energy density can be achieved without substantially impairing. More specifically, in the non-aqueous electrolyte secondary battery according to the present invention having a “charging voltage of 4.35 V or higher” and / or “N / P ratio of 1.05 or lower”, as described above, The capacity retention rate after 500 charge / discharge cycles can be 90% or more.
本発明の非水電解質二次電池は種々の態様で具現化され得る。 The nonaqueous electrolyte secondary battery of the present invention can be embodied in various modes.
例えば、本発明の非水電解質二次電池１００は、図２に示すように、好ましくは正極１、負極２およびセパレータ３が平面状に積層した平面積層構造を有している。換言すれば、本発明の好適な非水電解質二次電池は、いわゆるフォールディング型（捲回型）ではなく、“積層型”（即ち、“ラミネート型”または“スタック型”）である。 For example, as shown in FIG. 2, the nonaqueous electrolyte secondary battery 100 of the present invention preferably has a planar laminated structure in which a positive electrode 1, a negative electrode 2, and a separator 3 are laminated in a planar shape. In other words, the preferred nonaqueous electrolyte secondary battery of the present invention is not a so-called folding type (winding type) but a “stacked type” (that is, “laminated type” or “stacked type”).
“積層型”の非水電解質二次電池では、電極材層が全体として平面状に延在した形態となっているのに対して、“フォールディング型”の非水電解質二次電池では、電極材層が全体として巻回状に大きく湾曲した形態となっている。このような形態の相違に起因して、“積層型”と“フォールディング型”とでは電極材層にかかる応力がそもそも異なっており、それゆえ、電極材層の構成材および密度などはそれ相当に考慮する必要があるといえる。 In the “stacked type” non-aqueous electrolyte secondary battery, the electrode material layer extends in a planar shape as a whole, whereas in the “folding type” non-aqueous electrolyte secondary battery, the electrode material layer The layer as a whole is greatly curved in a winding shape. Due to the difference in form, the stress applied to the electrode material layer is different between the “stacked type” and the “folding type”. It can be said that it is necessary to consider.
“積層型”の場合、本発明の非水電解質二次電池は、平面状に延在した正極材層および負極材層が相互に積み重なった形態を有しているが、そのような平面状の電極材層のうち、特に正極材層に炭素繊維材が含まれていると共に、かかる正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下となっている。１つ例示すると、本発明に係る非水電解質二次電池は、図２に示すように平面積層構造を有する“積層型”であるところ、“充電電圧４．３５Ｖ以上”および“Ｎ／Ｐ比１．０５以下”を有していると共に、平面状に延在する正極材層における炭素繊維材の含有量が正極材層の全体基準で０．５重量％以上であり、かつ、そのように平面状に延在する正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下となっている。 In the case of the “stacked type”, the nonaqueous electrolyte secondary battery of the present invention has a configuration in which a positive electrode material layer and a negative electrode material layer extending in a planar shape are stacked on each other. Among the electrode material layers, a carbon fiber material is included in the positive electrode material layer, and the density of the positive electrode material layer is 3.85 g / cm 3 or more and 4.15 g / cm 3 or less. As an example, the non-aqueous electrolyte secondary battery according to the present invention is a “stacked type” having a planar stacked structure as shown in FIG. 2, and has a “charging voltage of 4.35 V or more” and an “N / P ratio”. 1.05 or less ", and the content of the carbon fiber material in the positive electrode material layer extending in a planar shape is 0.5% by weight or more based on the total amount of the positive electrode material layer, and as such The density of the positive electrode material layer extending in a planar shape is 3.85 g / cm 3 or more and 4.15 g / cm 3 or less.
また、本発明の１つの好適な実施態様では、正極材層に含まれる正極活物質の平均粒径が１０μｍ以上となっている。つまり、正極材層の正極活物質は好ましくは複数の粒状物から成るところ、かかる粒状物の平均粒径が１０μｍ以上となっている。正極活物質の平均粒径が１０μｍ以上となる場合、非水電解質二次電池において、所望の活物質としての機能を維持しつつも“局所発熱”の抑制に寄与し得る。正極活物質の平均粒径は、好ましくは１１μｍ以上、より好ましくは１２μｍ以上、更に好ましくは１３μｍ以上（例えば、１５μｍ以上または２０μｍ以上）である。なお、正極活物質の平均粒径の上限値は、活物質としての機能を損なわないものであれば特に制限はなく、例えば２５μｍ以上３０μｍ以下程度（例えば２８μｍ）であってよい。 Moreover, in one suitable embodiment of this invention, the average particle diameter of the positive electrode active material contained in a positive electrode material layer is 10 micrometers or more. That is, the positive electrode active material of the positive electrode material layer is preferably composed of a plurality of granular materials, and the average particle size of the granular materials is 10 μm or more. When the average particle diameter of the positive electrode active material is 10 μm or more, it can contribute to the suppression of “local heat generation” while maintaining the function as a desired active material in the nonaqueous electrolyte secondary battery. The average particle diameter of the positive electrode active material is preferably 11 μm or more, more preferably 12 μm or more, and further preferably 13 μm or more (for example, 15 μm or more or 20 μm or more). The upper limit of the average particle diameter of the positive electrode active material is not particularly limited as long as it does not impair the function as the active material, and may be, for example, about 25 μm to 30 μm (for example, 28 μm).
また、本発明の１つの好適な実施態様では、負極集電体の厚みが８μｍ以下となっている。例えば、負極集電体が金属箔（銅箔など）であって、かかる金属箔の厚みが８μｍ以下となっている。このように負極集電体の厚みが小さくなると、“局所発熱”の抑制に寄与しつつも非水電解質二次電池の小型化に寄与し得る。このような負極集電体の厚みは、好ましくは７μｍ以下、より好ましくは６μｍ以下である。なお、負極集電体の厚みの下限値は、集電体としての機能および／または構造強度を損なわないものであれば特に制限はなく、例えば２μｍ以上４μｍ以下程度（例えば３μｍ）であってよい。 In one preferred embodiment of the present invention, the thickness of the negative electrode current collector is 8 μm or less. For example, the negative electrode current collector is a metal foil (such as a copper foil), and the thickness of the metal foil is 8 μm or less. Thus, when the thickness of the negative electrode current collector is reduced, it can contribute to the miniaturization of the nonaqueous electrolyte secondary battery while contributing to the suppression of “local heat generation”. The thickness of such a negative electrode current collector is preferably 7 μm or less, more preferably 6 μm or less. The lower limit of the thickness of the negative electrode current collector is not particularly limited as long as it does not impair the function and / or structural strength as the current collector, and may be, for example, about 2 μm to 4 μm (for example, 3 μm). .
以上、本発明の実施形態について説明してきたが、あくまでも典型例を例示したに過ぎない。従って、本発明はこれに限定されず、種々の態様が考えられることを当業者は容易に理解されよう。 As mentioned above, although embodiment of this invention has been described, it has only illustrated the typical example to the last. Therefore, those skilled in the art will easily understand that the present invention is not limited to this, and various modes are conceivable.
本発明の非水電解質二次電池の効果を確認すべく以下の実証試験を行った。 In order to confirm the effect of the nonaqueous electrolyte secondary battery of the present invention, the following demonstration test was conducted.
実施例１〜７、比較例１〜４
（正極の作製）
正極活物質として平均粒径が１５μｍであるＬｉＣｏＯ２を９７．５重量％、導電助剤として直径１０ｎｍのカーボンナノチューブを１．０重量％、バインダーとしてポリフッ化ビニリデンを１．５重量％用いた。これらをＮＭＰ（Ｎ−メチル−２−ピロリドン）と混合して正極材スラリーを得た。次いで、正極材スラリーを厚さ１０μｍのアルミニウム箔の両面に均一に塗布してロールプレス機で圧延することで、両面で４２．０ｍｇ／ｃｍ２の正極材重量の正極を得た。このとき、圧延後の正極材層密度の調整によって、後述する放電状態の正極材層密度を３．７５ｇ／ｃｍ３以上４．２５ｇ／ｃｍ３以下となるようにした。
Examples 1-7, Comparative Examples 1-4
(Preparation of positive electrode)
As the positive electrode active material, 97.5% by weight of LiCoO 2 having an average particle diameter of 15 μm, 1.0% by weight of carbon nanotubes having a diameter of 10 nm as a conductive assistant, and 1.5% by weight of polyvinylidene fluoride as a binder were used. These were mixed with NMP (N-methyl-2-pyrrolidone) to obtain a positive electrode material slurry. Next, the positive electrode material slurry was uniformly applied to both surfaces of an aluminum foil having a thickness of 10 μm and rolled with a roll press to obtain a positive electrode having a positive electrode material weight of 42.0 mg / cm 2 on both surfaces. At this time, by adjusting the cathode material layer density after rolling, it was set to a positive electrode material layer density of the discharge state described later becomes 3.75 g / cm 3 or more 4.25 g / cm 3 or less.
（負極の作製）
負極活物質として人造黒鉛を９７．０重量％、バインダーとしてスチレンブタジエンゴムを２．０重量％、増粘剤としてカルボキシルメチルセルロースを１．０重量％用いた。これらを水と混合して負極材スラリーを得た。次いで、負極材スラリーを厚さ６μｍの銅箔の両面に均一に塗布してロールプレス機で負極材層密度が１．７０ｇ／ｃｍ３になるように圧延することで、両面で２０．８ｍｇ／ｃｍ２の負極材重量の負極を得た。
(Preparation of negative electrode)
97.0% by weight of artificial graphite was used as the negative electrode active material, 2.0% by weight of styrene butadiene rubber was used as the binder, and 1.0% by weight of carboxymethyl cellulose was used as the thickener. These were mixed with water to obtain a negative electrode material slurry. Next, the negative electrode material slurry was uniformly applied to both sides of a 6 μm thick copper foil, and rolled to a negative electrode material layer density of 1.70 g / cm 3 with a roll press, so that 20.8 mg / cm on both sides. A negative electrode having a weight of negative electrode material of cm 2 was obtained.
（電解液の形成）
エチレンカーボネートとジエチルカーボネートとの体積比が３：７となる溶液に１モルのＬｉＰＦ６を溶解して非水電解質液を形成した。
(Formation of electrolyte)
1 mol of LiPF 6 was dissolved in a solution having a volume ratio of ethylene carbonate and diethyl carbonate of 3: 7 to form a non-aqueous electrolyte solution.
（非水電解質二次電池の製造）
正極、負極および電解液を用いて定格容量が２．１Ａｈのラミネート型非水電解質二次電池を製造した。かかる非水電解質二次電池のＮ／Ｐ比（電池容量（Ｐ、ｍＡｈ）に対する負極の正極と対向する部分における可逆容量（Ｎ、ｍＡｈ）の割合）は１．０５であった。
(Manufacture of non-aqueous electrolyte secondary batteries)
A laminate type nonaqueous electrolyte secondary battery having a rated capacity of 2.1 Ah was manufactured using the positive electrode, the negative electrode, and the electrolytic solution. The N / P ratio (ratio of reversible capacity (N, mAh) in the portion facing the positive electrode of the negative electrode to battery capacity (P, mAh)) of the nonaqueous electrolyte secondary battery was 1.05.
（充放電後の放電状態の正負極材層厚みの測定）
容量確認後の完全放電状態の非水電解質二次電池をアルゴン雰囲気下のグローブボックス内で解体し、正極を取り出し、正極の厚みをデジタルマイクロメーター（ミツトヨ製ＭＤＨ−２５Ｍ）で測定した。得られた正極の厚みと正極材の塗布量から、正極材層の密度を算出した。
(Measurement of thickness of positive and negative electrode material layers in a discharged state after charge / discharge)
The non-aqueous electrolyte secondary battery in a fully discharged state after capacity confirmation was disassembled in a glove box under an argon atmosphere, the positive electrode was taken out, and the thickness of the positive electrode was measured with a digital micrometer (Mitutoyo MDH-25M). The density of the positive electrode material layer was calculated from the thickness of the obtained positive electrode and the coating amount of the positive electrode material.
（安全性試験）
上記で解体したものとは別の非水電解質二次電池を用い、２５℃の恒温槽中で釘刺しによる安全性試験を行った。具体的には、非水電解質二次電池を電圧４．３５Ｖまで１Ｃの電流値で定電流充電した後、電圧４．３５Ｖで１時間の定電圧充電を行い満充電状態にした。満充電状態の電池の中心部分に直径３ｍｍの鉄製の釘を１００ｍｍ／ｍｉｎの速度で刺して発火の有無（発火有：ＮＧ、発火無：Ｇ）を評価した。また、釘を刺した直後から１２０秒後までの電池表面の温度を電池表面に取り付けた熱電対で測定し、温度測定中における電池表面の最高温度を確認した。
(Safety test)
Using a non-aqueous electrolyte secondary battery different from the one disassembled above, a safety test was performed by nail penetration in a thermostatic bath at 25 ° C. Specifically, the nonaqueous electrolyte secondary battery was charged at a constant current up to a voltage of 4.35 V at a current value of 1 C, and then charged at a voltage of 4.35 V for 1 hour to obtain a fully charged state. The presence or absence of ignition (ignition: NG, no ignition: G) was evaluated by piercing an iron nail having a diameter of 3 mm at the center of a fully charged battery at a speed of 100 mm / min. In addition, the temperature of the battery surface from immediately after piercing the nail to 120 seconds later was measured with a thermocouple attached to the battery surface, and the maximum temperature of the battery surface during temperature measurement was confirmed.
（サイクル試験）
上記で安全性試験をしたものとは別の非水電解質二次電池を用い、２５℃の恒温槽中でサイクル試験を行った。具体的には、充電は電圧４．３５Ｖまで１Ｃの電流値で定電流充電した後、電圧４．３５Ｖで１時間の定電圧充電を行った。充電完了後、１０分間休止した後、電圧３．０Ｖまで１Ｃの電流値で定電流放電を行い、放電後１０分間の休止をした。このサイクルを５００サイクル繰り返した。１サイクル目の放電容量に対する５００サイクル後の放電容量の割合を５００サイクル後の容量維持率（％）とした。
(Cycle test)
A cycle test was conducted in a thermostatic bath at 25 ° C. using a non-aqueous electrolyte secondary battery different from that subjected to the safety test. Specifically, the charge was a constant current charge at a current value of 1 C up to a voltage of 4.35 V, and then a constant voltage charge for 1 hour at a voltage of 4.35 V. After charging was completed, it was paused for 10 minutes, and then a constant current discharge was performed at a current value of 1 C up to a voltage of 3.0 V, followed by a pause for 10 minutes after discharging. This cycle was repeated 500 cycles. The ratio of the discharge capacity after 500 cycles to the discharge capacity at the first cycle was defined as the capacity retention rate (%) after 500 cycles.
実施例８〜１１、比較例５
・実施例８
正極活物質として平均粒径が１５μｍであるＬｉＣｏＯ２を９８．０重量％、導電助剤として直径１０ｎｍのカーボンナノチューブを０．５重量％、バインダーとしてポリフッ化ビニリデンを１．５重量％用いて正極材層としたこと以外は実施例４と同様の方法で正極を作製した。
・実施例９
正極活物質として平均粒径が１５μｍであるＬｉＣｏＯ２を９７．０重量％、導電助剤として直径１０ｎｍのカーボンナノチューブを１．５重量％、バインダーとしてポリフッ化ビニリデンを１．５重量％用いて正極材層としたこと以外は実施例４と同様の方法で正極を作製した。
・実施例１０
正極活物質として平均粒径が１５μｍであるＬｉＣｏＯ２を９６．５重量％、導電助剤として直径１０ｎｍのカーボンナノチューブを２．０重量％、バインダーとしてポリフッ化ビニリデンを１．５重量％用いて正極材層としたこと以外は実施例４と同様の方法で正極を作製した。
・実施例１１
正極活物質として平均粒径が１５μｍであるＬｉＣｏＯ２を９５．５重量％、導電助剤として直径１０ｎｍのカーボンナノチューブを３．０重量％、バインダーとしてポリフッ化ビニリデンを１．５重量％用いて正極材層としたこと以外は実施例４と同様の方法で正極を作製した。
・比較例５
正極活物質として平均粒径が１５μｍであるＬｉＣｏＯ２を９７．５重量％、導電助剤としてアセチレンブラックを１．０重量％、バインダーとしてポリフッ化ビニリデンを１．５重量％用いて正極材層としたこと以外は実施例４と同様の方法で正極を作製した。
Examples 8-11, Comparative Example 5
Example 8
Positive electrode using 98.0% by weight of LiCoO 2 having an average particle diameter of 15 μm as a positive electrode active material, 0.5% by weight of carbon nanotubes having a diameter of 10 nm as a conductive additive, and 1.5% by weight of polyvinylidene fluoride as a binder. A positive electrode was produced in the same manner as in Example 4 except that the material layer was used.
Example 9
Positive electrode using 97.0% by weight of LiCoO 2 having an average particle diameter of 15 μm as a positive electrode active material, 1.5% by weight of carbon nanotubes having a diameter of 10 nm as a conductive additive, and 1.5% by weight of polyvinylidene fluoride as a binder. A positive electrode was produced in the same manner as in Example 4 except that the material layer was used.
Example 10
Positive electrode using 96.5% by weight of LiCoO 2 having an average particle diameter of 15 μm as a positive electrode active material, 2.0% by weight of carbon nanotubes having a diameter of 10 nm as a conductive assistant, and 1.5% by weight of polyvinylidene fluoride as a binder. A positive electrode was produced in the same manner as in Example 4 except that the material layer was used.
Example 11
Positive electrode using 95.5% by weight of LiCoO 2 having an average particle diameter of 15 μm as a positive electrode active material, 3.0% by weight of carbon nanotubes having a diameter of 10 nm as a conductive assistant, and 1.5% by weight of polyvinylidene fluoride as a binder. A positive electrode was produced in the same manner as in Example 4 except that the material layer was used.
Comparative example 5
A positive electrode material layer comprising 97.5% by weight of LiCoO 2 having an average particle diameter of 15 μm as a positive electrode active material, 1.0% by weight of acetylene black as a conductive additive, and 1.5% by weight of polyvinylidene fluoride as a binder, A positive electrode was produced in the same manner as in Example 4 except that.
結果を表１に示す。また、図３（ａ）および３（ｂ）には実施例１および比較例１に関する容量維持率の経時変化を示すと共に、釘刺し試験時の電池表面温度の経時変化を示す。 The results are shown in Table 1. 3 (a) and 3 (b) show the change over time of the capacity retention ratio with respect to Example 1 and Comparative Example 1, and also show the change over time of the battery surface temperature during the nail penetration test.
表１ならびに図３（ａ）および３（ｂ）からは少なくとも下記の事項を理解することができ、本発明の非水電解質二次電池が、局所発熱が好適に抑制されたものとなっていることが分かった。
● 炭素繊維材の含有（０．５重量％以上の含有）および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層を備えた非水電解質二次電池は、２５℃温度条件下で充放電サイクル５００回後の容量維持率が８９％以上９４％以下と８９％以上になるのに対して、そのような条件を有さない非水電解質二次電池は、２５℃温度条件下で充放電サイクル５００回後の容量維持率が７１％以上８４％以下と８９％未満となる。
● 炭素繊維材の含有（０．５重量％以上の含有）および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層を備えた非水電解質二次電池は、上記安全性試験において発火が生じないのに対して、そのような条件にない非水電解質二次電池は、発火が生じる。
●炭素繊維材の含有（０．５重量％以上の含有）および密度３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下の正極材層を備えた非水電解質二次電池の表面最高温度が１０５℃以上１３２℃以下となるのに対して、そのような条件にない非水電解質二次電池の表面最高温度が４２４℃以上５２１℃以下となる。
From Table 1 and FIGS. 3 (a) and 3 (b), at least the following matters can be understood, and the non-aqueous electrolyte secondary battery of the present invention is such that local heat generation is suitably suppressed. I understood that.
● The non-aqueous electrolyte secondary battery including the carbon fiber material (0.5 wt% or more) and the positive electrode material layer having a density of 3.85 g / cm 3 to 4.15 g / cm 3 is 25 ° C. Under the conditions, the capacity maintenance rate after 500 charge / discharge cycles is 89% or more and 94% or less and 89% or more, whereas a non-aqueous electrolyte secondary battery that does not have such a condition has a temperature of 25 ° C. Under these conditions, the capacity retention rate after 500 charge / discharge cycles is 71% or more and 84% or less and less than 89%.
● The non-aqueous electrolyte secondary battery including the carbon fiber material (containing 0.5% by weight or more) and the positive electrode material layer having a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less is the above-described safety. While non-ignition does not occur in the test, non-aqueous electrolyte secondary batteries not in such a condition are ignited.
● The maximum surface temperature of a non-aqueous electrolyte secondary battery having a positive electrode material layer containing carbon fiber material (containing 0.5% by weight or more) and having a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less While the temperature is 105 ° C. or more and 132 ° C. or less, the maximum surface temperature of the nonaqueous electrolyte secondary battery that does not satisfy such conditions is 424 ° C. or more and 521 ° C. or less.
本発明に係る非水電解質二次電池は、蓄電が想定される様々な分野に利用することができる。あくまでも例示にすぎないが、非水電解質二次電池は、モバイル機器などが使用される電気・情報・通信分野（例えば、携帯電話、スマートフォン、ノートパソコンおよびデジタルカメラなどのモバイル機器分野）、家庭・小型産業用途（例えば、電動工具、ゴルフカート、家庭用・介護用・産業用ロボットの分野）、大型産業用途（例えば、フォークリフト、エレベーター、湾港クレーンの分野）、交通システム分野（例えば、ハイブリッド車、電気自動車、バス、電車、電動アシスト自転車、電動二輪車などの分野）、電力系統用途（例えば、各種発電、ロードコンディショナー、スマートグリッド、一般家庭設置型蓄電システムなどの分野）、ならびに、宇宙・深海用途（例えば、宇宙探査機、潜水調査船などの分野）に利用することができる。 The nonaqueous electrolyte secondary battery according to the present invention can be used in various fields where power storage is assumed. The non-aqueous electrolyte secondary battery is merely an example, but the electric / information / communication field where mobile devices are used (for example, mobile devices such as mobile phones, smartphones, laptop computers and digital cameras), home / Small industrial applications (for example, power tools, golf carts, household / nursing / industrial robots), large industrial applications (forklifts, elevators, bay harbor cranes), transportation systems (for example, hybrid vehicles) , Electric vehicles, buses, trains, electric assist bicycles, electric motorcycles, etc.), power system applications (for example, various power generation, road conditioners, smart grids, general home storage systems, etc.), and space and deep seas To be used for applications (for example, space probes, submersible research vessels) It can be.
１ 正極
２ 負極
１０ 正極集電体
１５ 正極材層
２０ 負極集電体
２５ 正極材層
３ セパレータ
５０ 炭素繊維材
１００’非水電解質二次電池の積層構造体
１００ 非水電解質二次電池
DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 10 Positive electrode collector 15 Positive electrode material layer 20 Negative electrode collector 25 Positive electrode material layer 3 Separator 50 Carbon fiber material 100 'Nonaqueous electrolyte secondary battery laminated structure 100 Nonaqueous electrolyte secondary battery
Claims (13)
前記正極材層に炭素繊維材を含んで成り、前記正極材層の密度が３．８５ｇ／ｃｍ３以上４．１５ｇ／ｃｍ３以下であることを特徴とする、非水電解質二次電池。 A positive electrode in which a positive electrode material layer is provided on at least one side of the positive electrode current collector, a negative electrode in which a negative electrode material layer is provided on at least one side of the negative electrode current collector, a separator positioned between the positive electrode and the negative electrode, and A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte,
A nonaqueous electrolyte secondary battery comprising a carbon fiber material in the positive electrode material layer, wherein the positive electrode material layer has a density of 3.85 g / cm 3 or more and 4.15 g / cm 3 or less.
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