JP2009176720A - Manufacturing method of composite material for positive electrode of lithium battery - Google Patents
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Abstract
Description
本発明は、正極活物質粒子と繊維状炭素とを含む複合粒子から構成されるリチウム電池正極用複合材料の製造方法に関する。 The present invention relates to a method for producing a composite material for a lithium battery positive electrode composed of composite particles containing positive electrode active material particles and fibrous carbon.
近年、石油資源の高騰、国際的な地球環境保護運動の高まりを背景として、電気自動車、ハイブリッド自動車、燃料電池車の導入を促進すべく研究が行われている。これらの駆動システムには、補助用電源としてバッテリーが不可欠であり、しかも自動車の急発進急加速に追随できる高出力な電池が望まれている。また、車への重量負荷、燃費向上の観点から、エネルギー密度の高い電池が望まれる。このような背景から、二次電池の中で最もエネルギー密度が高く、かつ高出力を発現できるリチウムイオン二次電池が有望視されている。 In recent years, research has been conducted to promote the introduction of electric vehicles, hybrid vehicles, and fuel cell vehicles against the backdrop of soaring oil resources and the international movement for protecting the global environment. In these drive systems, a battery is indispensable as an auxiliary power source, and a high output battery capable of following the sudden start and rapid acceleration of an automobile is desired. In addition, a battery having a high energy density is desired from the viewpoint of weight load on the vehicle and improvement in fuel consumption. From such a background, a lithium ion secondary battery that has the highest energy density among the secondary batteries and can exhibit high output is promising.
一般にリチウムイオン二次電池は、リチウムイオン含有酸化物を含む正極と、炭素物質を含む負極とで電極が構成されている。正極では、リチウムイオン含有酸化物（正極活物質）自体の導電性が低いことから、導電性を向上させるために、カーボンブラックやカーボンファイバー等の導電材が添加されている。カーボンファイバーにおいては、近年、気相法による繊維径がナノオーダーのＶＧＣＦ（登録商標）やカーボンナノチューブが開発され、電池用途への応用が検討されている。 Generally, in a lithium ion secondary battery, an electrode is composed of a positive electrode including a lithium ion-containing oxide and a negative electrode including a carbon material. In the positive electrode, since the conductivity of the lithium ion-containing oxide (positive electrode active material) itself is low, a conductive material such as carbon black or carbon fiber is added to improve the conductivity. In recent years, VGCF (registered trademark) and carbon nanotubes having a fiber diameter of nano-order by a gas phase method have been developed for carbon fibers, and application to battery applications is being studied.
例えば特許文献１では、正極活物質とカーボンナノチューブ、グラファイトおよびバインダーを混合してペースト状にしたものを塗布し、正極を作製した例が開示されている。 For example, Patent Document 1 discloses an example in which a positive electrode active material, carbon nanotubes, graphite, and a binder are mixed and applied in a paste form to produce a positive electrode.
また、特許文献２には、粒径５〜３０μｍの球状正極活物質とカーボンナノファイバーを遠心ボールミルで機械的に強いせん断力を加えながら混合し、カーボンナノファイバーを分断して活物質表面に付着させる手法が試みられている。 Also, in Patent Document 2, a spherical positive electrode active material having a particle size of 5 to 30 μm and carbon nanofibers are mixed with a centrifugal ball mill while applying mechanically strong shearing force, and the carbon nanofibers are divided to adhere to the active material surface. Attempts have been made.
更に、特許文献３には、遷移金属化合物とリチウム化合物とを混合・焼成して得られた正極活物質と、炭素粉等の導電助剤とを噴霧乾燥して複合化するリチウム電池正極用複合材料の製造方法が開示されている。 Further, Patent Document 3 discloses a composite for a lithium battery positive electrode in which a positive electrode active material obtained by mixing and firing a transition metal compound and a lithium compound and a conductive auxiliary agent such as carbon powder are spray-dried to form a composite. A method for manufacturing the material is disclosed.
しかしながら、カーボンナノチューブのような繊維状炭素は、繊維状炭素同士が絡み合って糸玉状になっているため、特許文献１に記載されたような混合方法では、繊維状炭素をほぐして均一に正極活物質と混合することは非常に困難であり、カーボンナノチューブのポテンシャルを十分に引き出すことができない。 However, since fibrous carbon such as carbon nanotubes is in the form of a yarn ball by entanglement of the fibrous carbon, in the mixing method described in Patent Document 1, the fibrous carbon is loosened and the positive electrode is uniformly formed. It is very difficult to mix with the active material, and the potential of the carbon nanotube cannot be sufficiently extracted.
また、特許文献２に開示されているように、遠心ボールミルで機械的に強いせん断力を加えながら混合する方法では、カーボンナノファイバーが分断してしまうため、カーボンナノファイバーの特徴である高いアスペクト比による長距離の導電パスが阻害されてしまうという問題がある。 In addition, as disclosed in Patent Document 2, in the method of mixing while applying a mechanically strong shearing force with a centrifugal ball mill, the carbon nanofibers are divided, so that a high aspect ratio that is characteristic of the carbon nanofibers. There is a problem in that the long-distance conductive path due to is obstructed.
更に、特許文献３に記載の正極用複合材料の製造方法においても、噴霧乾燥に用いるスラリーを調製する際に繊維状炭素を正極活物質と均一に混合することが困難であるため、この製造方法における導電助剤として、炭素粉に代えて繊維状炭素を用いることは困難であった。 Furthermore, also in the manufacturing method of the composite material for positive electrodes described in Patent Document 3, it is difficult to uniformly mix the fibrous carbon with the positive electrode active material when preparing the slurry used for spray drying. It was difficult to use fibrous carbon instead of carbon powder as a conductive auxiliary in
そこで、本発明の目的は、高速放電特性に優れたリチウム電池を与える、Ｌｉの拡散経路が十分確保され、導電性が高い、リチウム電池正極用複合材料の製造方法を提供することにある。 Accordingly, an object of the present invention is to provide a method for producing a lithium battery positive electrode composite material that provides a lithium battery excellent in high-speed discharge characteristics, has a sufficiently secured Li diffusion path, and has high conductivity.
本発明者らは、溶媒中に正極活物質粒子と繊維状炭素とが十分に分散したスラリーを噴霧造粒することで、前記正極活物質粒子と前記繊維状炭素とを含有する造粒物が得られ、高速放電特性に優れた正極用複合材料となることを見出し、本発明を完成するに至った。 The present inventors spray granulate a slurry in which positive electrode active material particles and fibrous carbon are sufficiently dispersed in a solvent, whereby a granulated product containing the positive electrode active material particles and the fibrous carbon is obtained. As a result, it was found that the composite material for positive electrode was excellent in high-speed discharge characteristics, and the present invention was completed.
即ち、本発明のリチウム電池正極用複合材料の製造方法は、以下の工程１及び工程２を含む、正極活物質粒子と繊維状炭素とを含む複合粒子から構成されるリチウム電池正極用複合材料の製造方法である。
［工程１］溶媒中に正極活物質粒子と繊維状炭素とが分散した状態で含まれるスラリーを得る工程、
［工程２］前記工程１で得たスラリーを噴霧造粒して、前記正極活物質粒子と前記繊維状炭素とを含有する造粒物を得る工程。
That is, the method for producing a composite material for a lithium battery positive electrode of the present invention comprises a composite material for a lithium battery positive electrode comprising composite particles containing positive electrode active material particles and fibrous carbon, comprising the following steps 1 and 2. It is a manufacturing method.
[Step 1] A step of obtaining a slurry containing positive electrode active material particles and fibrous carbon dispersed in a solvent,
[Step 2] A step of spray granulating the slurry obtained in Step 1 to obtain a granulated product containing the positive electrode active material particles and the fibrous carbon.
本発明のリチウム電池正極用複合材料の製造方法によると、噴霧造粒に用いるスラリーとして、溶媒中に正極活物質粒子と繊維状炭素とが分散したものを使用することにより、導電性が高くかつＬｉの拡散経路が十分確保されるため、高速放電特性に優れたリチウム電池正極用複合材料が得られると考えられる。 According to the method for producing a composite material for a lithium battery positive electrode of the present invention, as a slurry used for spray granulation, by using a slurry in which positive electrode active material particles and fibrous carbon are dispersed in a solvent, high conductivity and Since a sufficient diffusion path of Li is secured, it is considered that a composite material for a lithium battery positive electrode having excellent high-speed discharge characteristics can be obtained.
本発明のリチウム電池正極用複合材料（以下、単に「正極用複合材料」という場合がある）の製造方法は、正極活物質粒子と繊維状炭素とを含む複合粒子から構成されるリチウム電池正極用複合材料の製造方法であって、以下で述べる工程１及び工程２を含むものである。まず、工程１では、溶媒中に正極活物質粒子と繊維状炭素とが分散した状態で含まれるスラリーを得る。 The method for producing a composite material for a lithium battery positive electrode of the present invention (hereinafter sometimes simply referred to as “a composite material for a positive electrode”) is for a lithium battery positive electrode composed of composite particles containing positive electrode active material particles and fibrous carbon. It is a manufacturing method of a composite material, Comprising: The process 1 and the process 2 which are described below are included. First, in step 1, a slurry is obtained that contains positive electrode active material particles and fibrous carbon dispersed in a solvent.
正極活物質粒子の材料としては、従来公知の何れの材料も使用でき、例えば、ＬｉＭｎ２Ｏ４などのＬｉ・Ｍｎ系複合酸化物、ＬｉＣｏＯ２などのＬｉ・Ｃｏ系複合酸化物、ＬｉＮｉＯ２などのＬｉ・Ｎｉ系複合酸化物、ＬｉＦｅＯ２などのＬｉ・Ｆｅ系複合酸化物などが挙げられ、ＬｉｘＣｏＯ２，ＬｉｘＮｉＯ２，ＭｎＯ２，ＬｉＭｎＯ２，ＬｉｘＭｎ２Ｏ４，ＬｉｘＭｎ２−ｙＯ４，α−Ｖ２Ｏ５，ＴｉＳ２等が挙げられる。なかでも、熱的安定性、及び容量、出力特性に優れるという観点から、ＬｉＭｎ２Ｏ４などのマンガン酸リチウム，ＬｉＣｏＯ２などのコバルト酸リチウム，ＬｉＮｉＯ２などのニッケル酸リチウムが好ましく、ＬｉＭｎ２Ｏ４などのマンガン酸リチウムがより好ましい。 As the material of the positive electrode active material particles, any conventionally known material can be used. For example, a Li / Mn composite oxide such as LiMn 2 O 4, a Li / Co composite oxide such as LiCoO 2 , LiNiO 2, etc. of Li · Ni-based composite oxide, is like Li · Fe-based composite oxides such as LiFeO 2, Li x CoO 2, Li x NiO 2, MnO 2, LiMnO 2, Li x Mn 2 O 4, Li x Mn 2-y O 4, α -V 2 O 5, TiS 2 and the like. Among these, from the viewpoint of excellent thermal stability, capacity, and output characteristics, lithium manganate such as LiMn 2 O 4, lithium cobaltate such as LiCoO 2, and lithium nickelate such as LiNiO 2 are preferable, and LiMn 2 O More preferred is lithium manganate such as 4 .
正極活物質粒子の平均凝集粒径としては、正極活物質の安全性や安定性、サイクル特性の観点から、好ましくは０．１μｍ以上、より好ましくは０．３μｍ以上、さらに好ましくは、０．５μｍ以上、また、反応性、高速放電性の観点から１０μｍ以下が好ましく、より好ましくは５μｍ以下、さらに好ましくは２μｍ以下である。これらの観点を総合すると、正極活物質粒子の平均凝集粒径は、０．１〜１０μｍが好ましく、０．３〜５μｍがより好ましく、０．５〜２μｍが更に好ましい。 The average agglomerated particle size of the positive electrode active material particles is preferably 0.1 μm or more, more preferably 0.3 μm or more, and further preferably 0.5 μm, from the viewpoints of safety and stability of the positive electrode active material and cycle characteristics. From the viewpoints of reactivity and high-speed discharge, the thickness is preferably 10 μm or less, more preferably 5 μm or less, and still more preferably 2 μm or less. Taking these viewpoints together, the average aggregate particle diameter of the positive electrode active material particles is preferably 0.1 to 10 μm, more preferably 0.3 to 5 μm, and still more preferably 0.5 to 2 μm.
繊維状炭素の選択については、次の観点が考慮される。即ち、本発明では各繊維が絡み合って糸玉状に凝集している繊維状炭素を、溶媒中で後述する程度の分散状態にまで分散せしめ（好ましくは分散剤を用いて分散せしめ）、これに正極活物質を混合することで繊維状炭素と正極活物質粒子が均一に混合したスラリーを形成し、それを噴霧乾燥し、前記正極活物質と前記繊維状炭素とを有する球状の複合粒子を構築させるのが好ましい。さらに噴霧造粒を行う際に、正極活物質に分散した繊維状炭素が絡まることにより、近傍の正極活物質が繊維状炭素により保持されていることが好ましく、包み込んだ状態で保持されて球状粒子が形成されることが更に好ましい。なお、ここで、「正極活物質粒子が繊維状炭素により保持されている」とは、噴霧造粒で得られる造粒物に含まれる正極活物質粒子が繊維状炭素により保持されて、造粒物の形状が維持される状態を指し、後述する方法により確認することができる。 The following aspects are considered for the selection of fibrous carbon. That is, in the present invention, the fibrous carbon in which the fibers are intertwined and aggregated in the form of a thread ball is dispersed in a solvent to a dispersion state as described later (preferably dispersed using a dispersant). By mixing the positive electrode active material, a slurry in which fibrous carbon and positive electrode active material particles are uniformly mixed is formed and spray-dried to construct spherical composite particles having the positive electrode active material and the fibrous carbon. It is preferable to do so. Further, when spray granulation is performed, fibrous carbon dispersed in the positive electrode active material is entangled, so that the positive electrode active material in the vicinity is preferably held by the fibrous carbon, and is held in an encapsulated state to be spherical particles More preferably, is formed. Here, “positive electrode active material particles are held by fibrous carbon” means that the positive electrode active material particles contained in the granulated product obtained by spray granulation are held by fibrous carbon and granulated. It refers to the state in which the shape of the object is maintained, and can be confirmed by the method described later.
繊維状炭素のアスペクト比については、上記のように各繊維状炭素が絡み合いながら正極活物質が繊維状炭素により保持されている造粒粒子を構築することが重要で、繊維径が細く、かつ繊維長が長い繊維状炭素を用いることが好ましい。このような観点から、繊維状炭素の繊維長（Ｌ）に対する繊維径（Ｗ）のアスペクト比、すなわちＬ／Ｗが重要になる。繊維状炭素のアスペクト比は、更に導電性の観点から、好ましくは５０以上、より好ましくは１００以上、更に好ましくは２００以上であり、繊維状炭素の分散性の観点から、好ましくは２００００以下、より好ましくは５０００以下、さらに好ましくは１０００以下である。これらの観点を総合すると、アスペクト比は、５０〜２００００が好ましく、１００〜５０００がより好ましく、２００〜１０００が更に好ましい。 Regarding the aspect ratio of the fibrous carbon, it is important to construct granulated particles in which the positive electrode active material is held by the fibrous carbon while the fibrous carbons are intertwined as described above. It is preferable to use fibrous carbon having a long length. From such a viewpoint, the aspect ratio of the fiber diameter (W) to the fiber length (L) of the fibrous carbon, that is, L / W is important. The aspect ratio of the fibrous carbon is preferably 50 or more, more preferably 100 or more, still more preferably 200 or more from the viewpoint of conductivity, and preferably 20000 or less, from the viewpoint of the dispersibility of the fibrous carbon. Preferably it is 5000 or less, More preferably, it is 1000 or less. From these viewpoints, the aspect ratio is preferably 50 to 20000, more preferably 100 to 5000, and still more preferably 200 to 1000.
同様の観点から、繊維状炭素はからまりやすい構造のものが好ましく、繊維状炭素の繊維長は、好ましくは５０ｎｍ以上、より好ましくは５００ｎｍ以上、更に好ましくは１μｍ以上である。また、本発明の正極用複合材料を用いて作製された、正極電極表面の平滑性の観点から、繊維状炭素の繊維長は、好ましくは５０μｍ以下、より好ましくは３０μｍ以下、さらに好ましくは１０μｍ以下である。これらの観点を総合すると、繊維状炭素の繊維長は、５０ｎｍ〜５０μｍが好ましく、５００ｎｍ〜３０μｍがより好ましく、１μｍ〜１０μｍが更に好ましい。また、繊維状炭素の繊維長と正極活物質粒子の平均凝集粒径（活物質粒径）の比（繊維状炭素の繊維長／活物質粒径）は、正極活物質を繊維状炭素に保持する観点から、好ましくは１以上、より好ましくは２以上、さらに好ましくは３以上である。また、同様の観点から、繊維状炭素の繊維長と活物質粒径の比は、好ましくは５００以下、より好ましくは１００以下、さらに好ましくは２０以下である。これらの観点を総合すると、繊維状炭素の繊維長と活物質粒径の比は、１〜５００が好ましく、２〜１００がより好ましく、３〜２０がさらに好ましい。 From the same viewpoint, it is preferable that the fibrous carbon is easily entangled, and the fiber length of the fibrous carbon is preferably 50 nm or more, more preferably 500 nm or more, and further preferably 1 μm or more. From the viewpoint of the smoothness of the surface of the positive electrode produced using the composite material for positive electrode of the present invention, the fiber length of the fibrous carbon is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less. It is. Taking these viewpoints together, the fiber length of the fibrous carbon is preferably 50 nm to 50 μm, more preferably 500 nm to 30 μm, and even more preferably 1 μm to 10 μm. In addition, the ratio of the fiber carbon fiber length to the average aggregated particle size (active material particle size) of the positive electrode active material particles (fiber length of fiber carbon / active material particle size) holds the positive electrode active material in the fibrous carbon. In view of the above, it is preferably 1 or more, more preferably 2 or more, and still more preferably 3 or more. From the same viewpoint, the ratio between the fiber length of the fibrous carbon and the active material particle size is preferably 500 or less, more preferably 100 or less, and still more preferably 20 or less. When these viewpoints are put together, 1-500 are preferable, as for the ratio of the fiber length of fibrous carbon, and an active material particle size, 2-100 are more preferable, and 3-20 are more preferable.
同様の観点から、繊維状炭素はからまりやすい構造のものが好ましいことと、正極活物質表面とより多く接触して導電経路を確立させる観点とから、繊維状炭素の繊維径は、１〜１０００ｎｍが好ましく、１〜５００ｎｍがより好ましく、１〜１００ｎｍが更に好ましく、１〜５０ｎｍが更により好ましい。 From the same point of view, the fiber diameter of the fibrous carbon is preferably 1 to 1000 nm from the viewpoint that the fibrous carbon has a structure that can easily become entangled and that the conductive path is established by making more contact with the surface of the positive electrode active material. Is preferred, 1 to 500 nm is more preferred, 1 to 100 nm is still more preferred, and 1 to 50 nm is even more preferred.
繊維状炭素としては、前述の好適なアスペクト比、繊維長及び繊維径を形成し易く、正極活物質粒子が繊維状炭素により保持された造粒物が噴霧造粒により得られ易い観点から、ポリアクリロニトリル（ＰＡＮ）に代表される高分子を原料とした繊維状炭素、ピッチを原料としたピッチ系繊維状炭素も使用可能であるが、カーボンナノチューブ（グラファイトの１枚面つまりグラフェンシートを巻いて筒状にした形状物（微粒子工学大系第I巻P651、株式会社フジ・テクノシステム））であって、炭化水素ガスを原料とする気相成長系の繊維状炭素（例えば、ＶＧＣＦ：登録商標）、アーク放電法、レーザー蒸発法、化学気相成長法などで得られる、いわゆる狭義のカーボンナノチューブ（以下、狭義のカーボンナノチューブを単にカーボンナノチューブという）などが好適に用いられる。より多くの導電経路を構築させる観点から、繊維径の細い繊維状炭素が好ましく、ＶＧＣＦやカーボンナノチューブが好適に用いられ、中でもカーボンナノチューブを用いることが好ましい。カーボンナノチューブは、例えば、ＨｅやＡｒ、ＣＨ４、Ｈ２などの雰囲気ガスのもとで、黒鉛電極をアーク放電で蒸発させるアーク放電法、ＮｉやＣｏ、Ｙ、Ｆｅなどの金属触媒を含む黒鉛電極をアーク放電で蒸発させるアーク放電法、Ｎｉ−Ｃｏ、Ｐｄ−Ｒｄなどの金属触媒を混ぜた黒鉛にＹＡＧレーザーを当て蒸発させ、Ａｒの気流で１２００℃程度に加熱された電気炉に送り出すレーザー蒸発法、触媒にペンタカルボニル鉄（Ｆｅ（ＣＯ）５）を用い、一酸化炭素を高圧で熱分解するＨｉＰＣＯ法等で得ることができる。カーボンナノチューブのアスペクト比については、例えば、炭化水素（ベンゼン等）と水素ガス等の雰囲気ガスの濃度比が小さいほど、生成するカーボンナノチューブの直径が細くなり、アスペクト比が大きくなる。また、反応時間が短いほど、生成するカーボンナノチューブの直径が細くなり、やはりアスペクト比が大きくなる。 From the viewpoint of easily forming the above-mentioned preferred aspect ratio, fiber length, and fiber diameter as fibrous carbon, and easily obtaining a granulated product in which positive electrode active material particles are held by fibrous carbon by spray granulation. Fibrous carbon made from a polymer represented by acrylonitrile (PAN) and pitch-based fibrous carbon made from pitch can also be used. Vapor-grown fibrous carbon (for example, VGCF: registered trademark) using a hydrocarbon gas as a raw material (fine particle engineering, Vol. I, P651, Fuji Techno System Co., Ltd.) , So-called narrow carbon nanotubes (hereinafter, simply defined as carbon nanotubes obtained by arc discharge method, laser evaporation method, chemical vapor deposition method, etc.) Such that the tube) is suitably used. From the viewpoint of constructing more conductive paths, fibrous carbon having a small fiber diameter is preferable, and VGCF and carbon nanotubes are preferably used. Among them, carbon nanotubes are preferably used. The carbon nanotube is, for example, an arc discharge method in which a graphite electrode is evaporated by arc discharge under an atmospheric gas such as He, Ar, CH 4 , or H 2 , and graphite containing a metal catalyst such as Ni, Co, Y, or Fe. An arc discharge method in which electrodes are evaporated by arc discharge, a YAG laser is applied to graphite mixed with a metal catalyst such as Ni-Co, Pd-Rd, and the laser is sent to an electric furnace heated to about 1200 ° C. with an Ar air stream. It can be obtained by an evaporation method, a HiPCO method in which pentacarbonyl iron (Fe (CO) 5 ) is used as a catalyst, and carbon monoxide is thermally decomposed at high pressure. As for the aspect ratio of the carbon nanotube, for example, the smaller the concentration ratio of the hydrocarbon (benzene or the like) and the atmospheric gas such as hydrogen gas, the smaller the diameter of the generated carbon nanotube and the larger the aspect ratio. In addition, the shorter the reaction time, the thinner the carbon nanotubes that are produced, and the higher the aspect ratio.
スラリー中の繊維状炭素の添加量は、正極材料の体積抵抗の低減の観点から、正極活物質１００重量部に対して、好ましくは０．０１重量部以上、より好ましくは、０．１重量部以上、更に好ましくは０．５重量部以上である。また、正極活物質表面への被覆性の観点から、好ましくは１５重量部以下、より好ましくは１０重量部以下、更に好ましくは５重量部以下である。これらの観点を総合すると、繊維状炭素の添加量は、０．０１〜１５重量部が好ましく、０．１〜１０重量部がより好ましく、０．５〜５重量部が更に好ましい。 From the viewpoint of reducing the volume resistance of the positive electrode material, the amount of fibrous carbon added in the slurry is preferably 0.01 parts by weight or more, more preferably 0.1 parts by weight with respect to 100 parts by weight of the positive electrode active material. Above, more preferably 0.5 parts by weight or more. Further, from the viewpoint of coverage on the surface of the positive electrode active material, it is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and still more preferably 5 parts by weight or less. When these viewpoints are put together, 0.01-15 weight part is preferable, as for the addition amount of fibrous carbon, 0.1-10 weight part is more preferable, and 0.5-5 weight part is still more preferable.
本発明では、繊維状炭素の他に導電性を補助する炭素材料を配合しても良い。そのような炭素材料としては、グラファイトやカーボンブラックが挙げられ、これらのうちカーボンブラックを使用することが好ましい。 In this invention, you may mix | blend the carbon material which assists electroconductivity other than fibrous carbon. Examples of such a carbon material include graphite and carbon black. Among these, it is preferable to use carbon black.
カーボンブラックとしては、サーマルブラック法、アセチレンブラック法等の分解法、チャンネルブラック法、ガスファーネスブラック法、オイルファーネスブラック法、松煙法、ランプブラック法等の不完全燃焼法のいずれの製法で製造されたものも使用できるが、導電性の観点からファーネスブラック、アセチレンブラックが好ましく用いられる。これらは単独で用いても良いし、２種以上を混合しても良い。 Carbon black is produced by any of the following methods: thermal black method, decomposition method such as acetylene black method, channel black method, gas furnace black method, oil furnace black method, pine smoke method, lamp black method, etc. However, furnace black and acetylene black are preferably used from the viewpoint of conductivity. These may be used alone or in combination of two or more.
カーボンブラックのＤＢＰ吸収量は、繊維状炭素の導電性を好適に補助する観点から、４０〜３００ｃｍ３／１００ｇが好ましく、８０〜２００ｃｍ３／１００ｇがより好ましい。 DBP absorption of carbon black, from the viewpoint of suitably assist the conductivity of the fibrous carbon is preferably 40~300cm 3 / 100g, 80~200cm 3 / 100g and more preferably.
繊維状炭素以外の炭素材料を添加する場合、このような炭素材料は、繊維状炭素の分散液の中に添加し、繊維状炭素とともに正極活物質粒子と複合するのに使用しても良い。また、繊維状炭素と正極活物質の分散液を噴霧造粒して得られた粒子と炭素材料を混合して、造粒物間の導電性を向上させる目的に利用しても良い。 When a carbon material other than fibrous carbon is added, such a carbon material may be added to a dispersion of fibrous carbon and used to combine with the positive electrode active material particles together with the fibrous carbon. Alternatively, particles obtained by spray granulating a dispersion of fibrous carbon and a positive electrode active material and a carbon material may be mixed and used for the purpose of improving the conductivity between the granulated products.
繊維状炭素以外の炭素材料の配合量は、導電性を補助しつつ造粒物の形状を保持する観点から、正極活物質１００重量部に対して、好ましくは０〜２０重量部、より好ましくは０〜１０重量部、更に好ましくは０〜５重量部である。 The blending amount of the carbon material other than fibrous carbon is preferably 0 to 20 parts by weight, more preferably 100 parts by weight with respect to 100 parts by weight of the positive electrode active material from the viewpoint of maintaining the shape of the granulated product while assisting conductivity. 0 to 10 parts by weight, more preferably 0 to 5 parts by weight.
炭素材料の総配合量、即ち、繊維状炭素と繊維状炭素以外の炭素材料の総配合量は、正極用複合材料の体積抵抗低減の観点から、正極活物質１００重量部に対して、好ましくは０．０２重量部以上、より好ましくは０．１重量部以上、更に好ましくは０．５重量部以上である。また、正極用複合材料のエネルギー密度を高める観点から、好ましくは３０重量部以下、より好ましくは２０重量部以下、更に好ましくは１０重量部以下である。これらの観点を総合すると、繊維状炭素と繊維状炭素以外の炭素材料の総配合量は、０．０２〜３０重量部が好ましく、０．１〜２０重量部がより好ましく、０．５〜１０重量部が更に好ましい。 The total blending amount of the carbon material, that is, the total blending amount of the carbon material other than the fibrous carbon and the fibrous carbon is preferably based on 100 parts by weight of the positive electrode active material from the viewpoint of reducing the volume resistance of the positive electrode composite material. It is 0.02 parts by weight or more, more preferably 0.1 parts by weight or more, and further preferably 0.5 parts by weight or more. Moreover, from a viewpoint of raising the energy density of the composite material for positive electrodes, Preferably it is 30 weight part or less, More preferably, it is 20 weight part or less, More preferably, it is 10 weight part or less. If these viewpoints are put together, 0.02-30 weight part is preferable, as for the total compounding quantity of carbon materials other than fibrous carbon and fibrous carbon, 0.1-20 weight part is more preferable, 0.5-10 Part by weight is more preferred.
本発明では、主として２つの工程、好ましくは３つの工程により正極用複合材料を作製する。 In the present invention, the composite material for positive electrode is produced mainly by two steps, preferably three steps.
まず［工程１］として、溶媒中に正極活物質粒子と繊維状炭素とが分散した状態で含まれるスラリーを得る。ここに、正極活物質粒子と繊維状炭素とが分散した状態とは、スラリーをサンプリングして所定濃度に希釈し、遅滞なく粒度分布測定装置で平均粒径を測定した際に、当該平均粒径が正極活物質の平均凝集粒径の１３０％以内になるような分散状態を指す（具体的な測定方法は後述する）。つまり、初期の凝集状態からこのような分散状態に移行することによって、測定される平均粒径が正極活物質の平均凝集粒径に近づき（繊維状炭素の分散状態もこの測定値に反映される）、この現象から上記の分散状態を把握することができる。 First, as [Step 1], a slurry containing positive electrode active material particles and fibrous carbon dispersed in a solvent is obtained. Here, the state in which the positive electrode active material particles and the fibrous carbon are dispersed means that when the slurry is sampled and diluted to a predetermined concentration and the average particle size is measured with a particle size distribution measuring device without delay, the average particle size is measured. Indicates a dispersion state in which the average aggregate particle size of the positive electrode active material is within 130% (a specific measurement method will be described later). That is, by shifting from the initial aggregated state to such a dispersed state, the measured average particle size approaches the average aggregated particle size of the positive electrode active material (the dispersed state of fibrous carbon is also reflected in this measured value. ), The above dispersion state can be grasped from this phenomenon.
このように正極活物質粒子と繊維状炭素とが分散した状態にする方法としては、繊維状炭素を溶媒中、分散剤を用いて分散させた後、正極活物質、場合によっては繊維状炭素以外の炭素材料を添加して、超音波を照射する方法が例示できる。 In this way, the positive electrode active material particles and the fibrous carbon are dispersed in a state in which the fibrous carbon is dispersed in a solvent using a dispersant and then the positive electrode active material, and in some cases other than the fibrous carbon. The method of adding the carbon material of this and irradiating an ultrasonic wave can be illustrated.
次いで、［工程２］として、工程１で得たスラリーを噴霧造粒して、正極活物質粒子と繊維状炭素とを含有する造粒物を得る。好ましくは、スラリーを噴霧し球形状の液滴を生成させた後、熱で溶媒を蒸発させて乾燥し、球形状の造粒粉体を形成する、いわゆる噴霧造粒を行うものである。 Next, as [Step 2], the slurry obtained in Step 1 is spray-granulated to obtain a granulated product containing positive electrode active material particles and fibrous carbon. Preferably, the slurry is sprayed to generate spherical droplets, and then the solvent is evaporated by heat and dried to form a spherical granulated powder, so-called spray granulation is performed.
更に工程２において又は工程２の後に、任意の工程である［工程３］として、造粒物から分散剤を除去して複合粒子を得ることが好ましい。 Furthermore, in Step 2 or after Step 2, it is preferable to obtain composite particles by removing the dispersant from the granulated product as [Step 3], which is an optional step.
また、上記３つの工程により得られた粒子間の導電パスを好適に構築するために、繊維状炭素以外の炭素材料を混合する工程を加えても良い。 Moreover, in order to construct | assemble the electrically conductive path between the particles obtained by the said three processes suitably, you may add the process of mixing carbon materials other than fibrous carbon.
工程１で分散に用いる溶媒としては、Ｎ−メチル−２−ピロリドン（ＮＭＰ、沸点２０２℃）、ジメチルホルムアミド（ＤＭＦ、沸点１５３℃）、ジメチルアセトアミド（沸点１６５℃）、水（沸点１００℃）、メチルエチルケトン（沸点７９．５℃）、テトラヒドロフラン（沸点６６℃）、アセトン（沸点５６．３℃）、エタノール（沸点７８．３℃）、酢酸エチル（沸点７６．８℃）などが好適に用いられる。コスト面および繊維状炭素の分散のさせやすさの観点から水を用いることが好ましい。 As a solvent used for dispersion in Step 1, N-methyl-2-pyrrolidone (NMP, boiling point 202 ° C.), dimethylformamide (DMF, boiling point 153 ° C.), dimethylacetamide (boiling point 165 ° C.), water (boiling point 100 ° C.), Methyl ethyl ketone (boiling point 79.5 ° C.), tetrahydrofuran (boiling point 66 ° C.), acetone (boiling point 56.3 ° C.), ethanol (boiling point 78.3 ° C.), ethyl acetate (boiling point 76.8 ° C.) and the like are preferably used. Water is preferably used from the viewpoint of cost and ease of dispersion of fibrous carbon.
工程１における溶媒の使用量は、繊維状炭素を十分に分散させ、かつ、工程２である噴霧造粒を行うのに十分な粘度とする観点から、正極活物質１００重量部に対して、６０重量部以上が好ましく、１００重量部以上がより好ましく、２００重量部以上が更に好ましい。また、生産性の観点から、３０００重量部以下が好ましく、２０００重量部以下がより好ましく、１５００重量部以下が更に好ましい。 The amount of the solvent used in step 1 is 60 with respect to 100 parts by weight of the positive electrode active material from the viewpoint of sufficiently dispersing the fibrous carbon and setting the viscosity to be sufficient for spray granulation which is step 2. It is preferably at least 100 parts by weight, more preferably at least 200 parts by weight. Moreover, from a viewpoint of productivity, 3000 weight part or less is preferable, 2000 weight part or less is more preferable, 1500 weight part or less is still more preferable.
工程１では、分散剤を使用することも可能であり、その場合に使用する分散剤としては、アニオン性、ノニオン性もしくはカチオン性界面活性剤、または高分子分散剤を用いることが出来る。繊維状炭素は、直径が１０００ｎｍ以下の微細炭素繊維であるが、炭素六角網面のネットワークが円筒状に延びた構造を呈している。このような構造と親和性の良好な分散剤の特徴として、炭素六角網面とサイズおよび形状が似ている芳香族の官能基を有しているものや、脂環化合物を官能基ユニットとして有する分散剤が特に繊維状炭素に吸着しやすい性質を有しているため好ましい。つまり、使用する分散剤としては、芳香族環及び／又は脂肪族環を含む官能基を有することが好ましい。 In step 1, a dispersant can be used, and as the dispersant used in that case, an anionic, nonionic or cationic surfactant, or a polymer dispersant can be used. Fibrous carbon is a fine carbon fiber having a diameter of 1000 nm or less, but has a structure in which a network of carbon hexagonal mesh surfaces extends in a cylindrical shape. Dispersants with good structure and affinity are characterized by aromatic functional groups that are similar in size and shape to the carbon hexagonal network surface, and alicyclic compounds as functional group units. The dispersant is preferable because it has a property of being easily adsorbed on the fibrous carbon. That is, the dispersant to be used preferably has a functional group containing an aromatic ring and / or an aliphatic ring.
高分子分散剤としては種々の化合物を使用することができるが、分子内に複数のカルボキシル基を有するポリカルボン酸系高分子分散剤、分子内に複数のアミノ基を有するポリアミン系高分子分散剤、分子内に複数のアミド基を有する高分子分散剤や分子内に複数の多環式芳香族化合物を含有する高分子分散剤が好ましい。 Although various compounds can be used as the polymer dispersant, a polycarboxylic acid polymer dispersant having a plurality of carboxyl groups in the molecule and a polyamine polymer dispersant having a plurality of amino groups in the molecule A polymer dispersant having a plurality of amide groups in the molecule and a polymer dispersant containing a plurality of polycyclic aromatic compounds in the molecule are preferred.
ポリカルボン酸系高分子分散剤としてはポリ（メタ）アクリル酸とその誘導体が挙げられる。その誘導体の具体例としては、（メタ）アクリル酸と（メタ）アクリル酸エステルとの共重合体、（メタ）アクリル酸と無水マレイン酸との共重合体、更にはそのアミド化物やエステル化物、（メタ）アクリル酸とマレイン酸との共重合体、および（メタ）アクリル酸ユニットを持つくし型ポリマー等を挙げることができる。なお、本明細書において、（メタ）アクリル酸は、アクリル酸又はメタクリル酸を指す。 Examples of the polycarboxylic acid polymer dispersant include poly (meth) acrylic acid and derivatives thereof. Specific examples of the derivative include a copolymer of (meth) acrylic acid and (meth) acrylic acid ester, a copolymer of (meth) acrylic acid and maleic anhydride, and an amidated or esterified product thereof. Examples thereof include a copolymer of (meth) acrylic acid and maleic acid, and a comb polymer having a (meth) acrylic acid unit. In the present specification, (meth) acrylic acid refers to acrylic acid or methacrylic acid.
ポリアミン系高分子分散剤としてはポリアルキレンアミンおよびその誘導体、ポリアリルアミンおよびその誘導体、ポリジアリルアミンおよびその誘導体、ポリＮ，Ｎ−ジメチルアミノエチルメタクリレートおよびその誘導体、更には上記ポリアミンにポリエステルをグラフトさせたくし型ポリマー等を挙げることができる。 Examples of the polyamine-based polymer dispersant include polyalkyleneamine and derivatives thereof, polyallylamine and derivatives thereof, polydiallylamine and derivatives thereof, poly N, N-dimethylaminoethyl methacrylate and derivatives thereof, and polyesters to be grafted onto the above polyamines. Type polymer and the like.
分子内に複数のアミド基を有する高分子分散剤としては、縮合反応によって得られるポリアミドおよびその誘導体やポリビニルピロリドンおよびその誘導体やポリＮ，Ｎ−ジメチルアクリルアミドおよびその誘導体、更にはこれらポリアミドにポリエステルやポリアルキレングリコールをグラフトさせたくし型ポリマー等を挙げることができる。 Examples of the polymer dispersant having a plurality of amide groups in the molecule include polyamides obtained by condensation reaction and derivatives thereof, polyvinylpyrrolidone and derivatives thereof, poly N, N-dimethylacrylamide and derivatives thereof, and polyesters and derivatives thereof. Examples thereof include a comb-type polymer grafted with polyalkylene glycol.
多環式芳香族化合物を含有する高分子分散剤としては、ピレンやキナクリドン骨格を有するビニルモノマーと各種モノマーとの共重合体を挙げることが出来る。 Examples of the polymeric dispersant containing a polycyclic aromatic compound include copolymers of vinyl monomers having a pyrene or quinacridone skeleton and various monomers.
これらの分散剤は単独で、あるいは二種以上の分散剤を混合して用いることができる。分散剤を用いる場合の好適な添加量は、スラリーの分散を好適に行いながらスラリー粘度を下げる観点から、スラリーに対して０．０５〜２０重量％であり、より好ましくは０．０５〜１０重量％である。 These dispersing agents can be used alone or in admixture of two or more kinds of dispersing agents. A suitable addition amount in the case of using a dispersant is 0.05 to 20% by weight, more preferably 0.05 to 10% by weight based on the slurry from the viewpoint of lowering the slurry viscosity while suitably dispersing the slurry. %.
また、分散剤が本発明の正極用複合材料に残留していると、それ自体が抵抗成分となり、電池の高速放電性能を阻害する場合がある。従って、後ほど詳細に説明する工程３のように、分散剤を除去するのが好ましい。除去法は、分散剤を洗浄により除去する手法と熱処理により分解する手法が主として用いられるが、そのような観点から、洗浄しやすい分散剤として、界面活性剤を用いることが好ましい。また、熱処理により完全に分解し、カウンターイオンを残留させず気化してしまう性質のものが好ましい観点から、ノニオン性の界面活性剤が更に好ましい。 Further, if the dispersant remains in the positive electrode composite material of the present invention, the dispersant itself becomes a resistance component, which may hinder the high-speed discharge performance of the battery. Accordingly, it is preferable to remove the dispersant as in Step 3 described in detail later. As the removal method, a method of removing the dispersant by washing and a method of decomposing by the heat treatment are mainly used. From such a viewpoint, it is preferable to use a surfactant as a dispersant that is easy to wash. In addition, a nonionic surfactant is more preferable from the viewpoint that it can be completely decomposed by heat treatment and can be vaporized without leaving counter ions.
工程１における分散剤の配合量は、繊維状炭素を分散させる観点から、繊維状炭素１００重量部に対して、好ましくは１重量部以上、より好ましくは５重量部以上、１０重量部以上が更に好ましい。また、工程３である分散剤除去工程での負荷を軽減させる観点から、好ましくは２００重量部以下、より好ましくは１５０重量部以下、１００重量部以下が更に好ましい。これらの観点を総合すると、分散剤の配合量は、１〜２００重量部が好ましく、５〜１５０重量部がより好ましく、１０〜１００重量部が更に好ましい。 From the viewpoint of dispersing the fibrous carbon, the blending amount of the dispersant in step 1 is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and more preferably 10 parts by weight or more with respect to 100 parts by weight of the fibrous carbon. preferable. Further, from the viewpoint of reducing the load in the dispersant removing step, which is step 3, it is preferably 200 parts by weight or less, more preferably 150 parts by weight or less and even more preferably 100 parts by weight or less. Taking these viewpoints together, the amount of the dispersing agent is preferably 1 to 200 parts by weight, more preferably 5 to 150 parts by weight, and still more preferably 10 to 100 parts by weight.
繊維状炭素をスラリー化する際、分散に先立って解凝集（予備分散）を行うことが好ましい。即ち、カーボンナノファイバー等の繊維状炭素は、一般的に糸玉状に凝集しているが、これを分散剤で分散する前に、ある程度機械的に解砕し、解凝集させることが好ましい。このような事前の解凝集には、乾式粉砕機を用いることが好ましく、具体的には、ロータースピードミル、ハンマーミル等の衝撃式粉砕機、乾式転動ボールミル、乾式振動ボールミル、乾式遊星ミル、媒体撹拌ミル等の乾式媒体粉砕機、ジェットミル等の気流式粉砕機、などを用いる方法が挙げられる。なかでも、適度な粉砕を行う観点から、ロータースピードミル、ハンマーミル等の衝撃式粉砕機を用いる方法が好ましい。 When slurrying the fibrous carbon, it is preferable to perform deagglomeration (preliminary dispersion) prior to dispersion. That is, fibrous carbon such as carbon nanofibers is generally aggregated in the form of yarn balls, but it is preferable to disintegrate mechanically to some extent and disaggregate before dispersing it with a dispersant. For such prior deagglomeration, it is preferable to use a dry pulverizer, specifically, an impact pulverizer such as a rotor speed mill and a hammer mill, a dry rolling ball mill, a dry vibration ball mill, a dry planetary mill, Examples thereof include a method using a dry medium pulverizer such as a medium stirring mill, an airflow pulverizer such as a jet mill, and the like. Among these, a method using an impact pulverizer such as a rotor speed mill or a hammer mill is preferable from the viewpoint of appropriate pulverization.
工程１では、分散剤を使って溶媒中で繊維状炭素を分散させることが好ましいが、その際、分散を促進するために、分散剤をスラリーに加えながら、もしくは加える前又は後、好ましくは後に、分散機を用いて強制的に分散することがより好ましい。分散機としては、例えば超音波型分散機、攪拌型分散機、高速回転せん断型分散機、ミル型分散機、高圧噴射型分散機などが挙げられるが、強制分散させる工程に使用する場合、超音波型分散機、高圧噴射型分散機が好適に用いられる。 In step 1, it is preferable to disperse the fibrous carbon in a solvent using a dispersant. At this time, in order to promote the dispersion, the dispersant is added to the slurry, or before or after the addition, preferably after. It is more preferable to forcibly disperse using a disperser. Examples of the disperser include an ultrasonic disperser, a stirring disperser, a high-speed rotary shear disperser, a mill disperser, a high-pressure jet disperser, and the like. Sonic dispersers and high-pressure jet dispersers are preferably used.
工程１により、繊維状炭素は溶媒中に分散するが、その際の繊維状炭素の平均凝集粒径としては、繊維状炭素を単繊維までほぐす観点から、０．１〜４０μｍが好ましく、０．１〜１０μｍがより好ましく、０．１〜５μｍが更に好ましい。 Although the fibrous carbon is dispersed in the solvent by the step 1, the average aggregate particle diameter of the fibrous carbon at that time is preferably 0.1 to 40 μm from the viewpoint of loosening the fibrous carbon to single fibers. 1-10 micrometers is more preferable and 0.1-5 micrometers is still more preferable.
工程１で得られるスラリーの固形分濃度（正極活物質＋繊維状炭素＋その他の炭素材料＋分散剤）としては、次工程の噴霧造粒の生産性を高める観点から、１重量％以上が好ましく、２重量％以上がより好ましく、５重量％以上が更に好ましい。また、工程２で得られる造粒物の粒径を好ましい範囲にする観点から、６０重量％以下が好ましく、５０重量％以下がより好ましく、４０重量％以下が更に好ましい。これらの観点を総合すると、スラリーの固形分濃度は、１〜６０重量％が好ましく、２〜５０重量％がより好ましく、５〜４０重量％が更に好ましい。また、工程１で得られるスラリーの粘度は、工程２で得られる造粒物の粒径を好ましい範囲に制御する観点から、５０００ｍＰａ・ｓ以下が好ましく、１０００ｍＰａ・ｓ以下がより好ましく、１００ｍＰａ・ｓ以下が更に好ましい。 The solid content concentration of the slurry obtained in step 1 (positive electrode active material + fibrous carbon + other carbon material + dispersant) is preferably 1% by weight or more from the viewpoint of increasing the productivity of spray granulation in the next step. 2% by weight or more is more preferable, and 5% by weight or more is more preferable. Moreover, from a viewpoint which makes the particle size of the granulated material obtained at the process 2 into a preferable range, 60 weight% or less is preferable, 50 weight% or less is more preferable, and 40 weight% or less is still more preferable. From these viewpoints, the solid content concentration of the slurry is preferably 1 to 60% by weight, more preferably 2 to 50% by weight, and still more preferably 5 to 40% by weight. Further, the viscosity of the slurry obtained in step 1 is preferably 5000 mPa · s or less, more preferably 1000 mPa · s or less, and more preferably 100 mPa · s, from the viewpoint of controlling the particle size of the granulated product obtained in step 2 within a preferable range. The following is more preferable.
工程２では、工程１で得られたスラリーを噴霧造粒するが、噴霧造粒の方法としては、スラリーをノズル、アトマイザー等により液滴化し、これをごく短時間に乾燥する、いわゆる噴霧乾燥法のほか、前記液滴を短時間に凍結した後、減圧下等で乾燥する噴霧凍結乾燥法や、噴霧乾燥と焼成を組み合わせた噴霧熱分解法等の方法を用いることができる。このうち、噴霧乾燥法が好ましい。 In step 2, the slurry obtained in step 1 is spray-granulated. As a method of spray granulation, the slurry is formed into droplets with a nozzle, an atomizer, etc., and dried in a very short time. In addition, a method such as a spray freeze-drying method in which the droplets are frozen in a short time and then dried under reduced pressure, or a spray pyrolysis method in which spray drying and baking are combined can be used. Of these, the spray drying method is preferred.
工程２において、噴霧により得られた液滴の乾燥温度は、繊維状炭素や他の炭素材料が、燃焼されない温度で乾燥することが好ましく、具体的には、４００℃以下が好ましく、３００℃以下がより好ましい。 In step 2, the drying temperature of the droplets obtained by spraying is preferably dried at a temperature at which the fibrous carbon or other carbon material is not combusted. Specifically, the drying temperature is preferably 400 ° C. or lower, and 300 ° C. or lower. Is more preferable.
工程２における造粒物の平均凝集粒径は、Ｌｉの挿入・脱離能を向上させ、かつ塗膜の平滑性を維持する観点から、２０μｍ以下が好ましく、１５μｍ以下がより好ましく、１０μｍ以下が更に好ましい。また、電池の正極として、塗膜を作製する際に、バインダーの量を減らす観点から、１μｍ以上が好ましく、３μｍ以上がより好ましく、５μｍ以上が更に好ましい。これらの観点を総合すると、造粒物の平均凝集粒径は、１〜２０μｍが好ましく、３〜１５μｍがより好ましく、５〜１０μｍが更に好ましい。 The average agglomerated particle diameter of the granulated product in step 2 is preferably 20 μm or less, more preferably 15 μm or less, and more preferably 10 μm or less from the viewpoint of improving the insertion / desorption ability of Li and maintaining the smoothness of the coating film. Further preferred. Moreover, when producing a coating film as a positive electrode of a battery, 1 micrometer or more is preferable from a viewpoint of reducing the quantity of a binder, 3 micrometers or more are more preferable, and 5 micrometers or more are still more preferable. Taking these viewpoints together, the average aggregate particle size of the granulated product is preferably 1 to 20 μm, more preferably 3 to 15 μm, and even more preferably 5 to 10 μm.
工程３は、工程２により得られた粒子内に、繊維状炭素を分散するために加えた分散剤が含まれる場合に有効である。分散剤が残留していると、分散剤が抵抗成分となってしまい、電池の高速放電特性を阻害するだけでなく、電池中で分解することによる、ガスの発生や、充放電のサイクル特性の低下要因になる。したがって、残留した分散剤を除去する必要があり、これの処理が工程３である。 Step 3 is effective when the particles obtained in Step 2 contain a dispersant added to disperse the fibrous carbon. If the dispersant remains, the dispersant becomes a resistance component, which not only hinders the high-speed discharge characteristics of the battery, but also the generation of gas due to decomposition in the battery and the cycle characteristics of charge / discharge. It becomes a decrease factor. Therefore, it is necessary to remove the remaining dispersant, and this process is step 3.
具体的な手法としては２つの手法が挙げられ、（１）分散剤を溶解できる溶媒で洗浄して除去する方法と、（２）分散剤を熱処理により分解気化させて除去する方法である。（１）の方法はほとんどの分散剤に適用できる面で好ましく、（２）の方法は、（１）の方法よりも低コストで生産性の高い手法である面で好ましい。 Specific methods include two methods: (1) a method in which the dispersant is removed by washing with a solvent that can dissolve the dispersant, and (2) a method in which the dispersant is removed by decomposition and vaporization by heat treatment. The method (1) is preferable because it can be applied to most dispersants, and the method (2) is preferable because it is a lower cost and higher productivity method than the method (1).
工程３において、熱処理を行って分散剤を除去する場合（上記（２）の手法）、分散剤を効率よく分解させる観点から、加熱温度は、１００℃以上が好ましく、１５０℃以上がより好ましい。また、繊維状炭素を分解させない観点から、４００℃以下が好ましく、３００℃以下がより好ましい。 In Step 3, when the heat treatment is performed to remove the dispersant (method (2) above), the heating temperature is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, from the viewpoint of efficiently decomposing the dispersant. Moreover, from a viewpoint which does not decompose fibrous carbon, 400 degrees C or less is preferable and 300 degrees C or less is more preferable.
以上の工程１〜３によって得られた正極用複合材料の形状は、球形状であるが、必ずしも真球状のもののみが得られるわけではなく、粒子表面に多少凸凹があるもの、球全体が多少歪んだもの、一部がへこんだものや、欠けたもの、球状粒子がいくつか合体して凝集したものなど、噴霧造粒で得られうる粒子形態のものが得られうる。また、繊維状炭素として、繊維径の大きいカーボンファイバーを含有する場合、カーボンファイバーが、球形状の粒子表面から突き出た形態を示すものも得られうる。 The shape of the composite material for a positive electrode obtained by the above steps 1 to 3 is a spherical shape, but it is not always possible to obtain only a true spherical shape. Particles that can be obtained by spray granulation, such as those that are distorted, partly dented, chipped, or agglomerated by aggregation of several spherical particles, can be obtained. Moreover, when carbon fiber with a large fiber diameter is contained as the fibrous carbon, a carbon fiber having a form protruding from the spherical particle surface can be obtained.
工程３を経て得られた複合粒子の平均凝集粒径は、電池の正極として、塗膜を作製する際に、バインダーの量を減らす観点から、１μｍ以上が好ましく、３μｍ以上がより好ましく、５μｍ以上が更に好ましい。また、本複合粒子を用いて得られる正極電極の表面性の観点から、好ましくは２０μｍ以下、より好ましくは１５μｍ以下、１０μｍ以下が更に好ましい。これらの観点を総合すると、複合粒子の平均凝集粒径は、１〜２０μｍが好ましく、３〜１５μｍがより好ましく、５〜１０μｍが更に好ましい。 The average aggregate particle diameter of the composite particles obtained through the step 3 is preferably 1 μm or more, more preferably 3 μm or more, and more preferably 5 μm or more from the viewpoint of reducing the amount of the binder when producing a coating film as the positive electrode of the battery. Is more preferable. Moreover, from the viewpoint of the surface property of the positive electrode obtained using the composite particles, it is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. Taking these viewpoints together, the average aggregate particle size of the composite particles is preferably 1 to 20 μm, more preferably 3 to 15 μm, and even more preferably 5 to 10 μm.
本発明で得られたリチウム電池正極用複合材料の体積抵抗は、正極において十分な導電性を付与する観点から、０〜３Ω・ｃｍが好ましく、０〜２Ω・ｃｍがより好ましく、０〜１．５Ω・ｃｍが更に好ましい。 The volume resistance of the lithium battery positive electrode composite material obtained in the present invention is preferably 0 to 3 Ω · cm, more preferably 0 to 2 Ω · cm, and more preferably 0 to 1. 5Ω · cm is more preferable.
また、得られたリチウム電池正極用複合材料は、繊維状炭素の絡みあった部分の隙間や正極活物質間の隙間により微細孔が形成され易い。微細孔が形成される場合、Ｌｉの移動がスムーズに行われる観点から０．０１〜１μｍの細孔容量の合計が、０．３ｍｌ／ｇ以上が好ましく、０．４ｍｌ／ｇ以上がより好ましい。また、バインダー添加量を少なくさせる観点から、０．０１〜１μｍの細孔容量の合計が０．８ｍｌ／ｇ以下が好ましく、０．６ｍｌ／ｇ以下がより好ましい。 In addition, in the obtained composite material for a lithium battery positive electrode, micropores are easily formed due to the gap between the portions where the fibrous carbon is entangled and the gap between the positive electrode active materials. When fine pores are formed, the total pore volume of 0.01 to 1 μm is preferably 0.3 ml / g or more, more preferably 0.4 ml / g or more, from the viewpoint of smooth movement of Li. Further, from the viewpoint of reducing the amount of binder added, the total pore volume of 0.01 to 1 μm is preferably 0.8 ml / g or less, and more preferably 0.6 ml / g or less.
本発明の製造方法によれば、正極活物質粒子が繊維状炭素により保持された構造を容易に得ることができるため、全ての正極活物質粒子に導電ネットワークが構築され、非常に導電性が高い正極用複合材料が得られると考えられる。また、繊維状炭素の絡み合いによって微細な空間ができ易いため、この隙間を介してリチウムイオンがスムーズに拡散できることから、高速放電に優れた正極用複合材料が得られると考えられる。さらに、繊維状炭素からなるネットが正極活物質を包み込んでいる場合は、このネットが柔軟性に富んでいるため、電極を作製する際のプレスにより球形構造が押しつぶされて崩壊することを抑制できる。このようなことから、本発明の正極用複合材料は、従来のものよりも電池の内部抵抗を小さくできるため、高速放電特性に優れたリチウム電池を提供することができると考えられる。 According to the production method of the present invention, since a structure in which the positive electrode active material particles are held by fibrous carbon can be easily obtained, a conductive network is constructed in all the positive electrode active material particles, and the conductivity is very high. It is considered that a composite material for positive electrode can be obtained. In addition, since a fine space is easily formed by the entanglement of fibrous carbon, lithium ions can be smoothly diffused through the gap, so that it is considered that a positive electrode composite material excellent in high-speed discharge can be obtained. Furthermore, when the net made of fibrous carbon wraps the positive electrode active material, the net is rich in flexibility, so that it is possible to suppress the spherical structure from being crushed and collapsed by the press when manufacturing the electrode. . For this reason, the composite material for positive electrode according to the present invention can reduce the internal resistance of the battery as compared with the conventional one, and thus it is considered that a lithium battery excellent in high-speed discharge characteristics can be provided.
つまり、本発明のリチウム電池正極用複合材料の複合粒子は、繊維状炭素の少なくとも一部が正極活物質粒子間隙に存在する形態を有することが好ましく、繊維状炭素の一部が正極活物質粒子間隙に存在するとともに、繊維状炭素が正極活物質粒子を網目状に包み込んだ形態を有することがより好ましい。このような形態は、後述する実施例で示すように、走査型電子顕微鏡観察により確認することができる。 That is, the composite particle of the composite material for a lithium battery positive electrode of the present invention preferably has a form in which at least a part of fibrous carbon is present in the gap between the positive electrode active material particles, and a part of the fibrous carbon is positive electrode active material particle. More preferably, the carbon atoms are present in the gaps and have a form in which the fibrous carbon wraps the positive electrode active material particles in a network. Such a form can be confirmed by observation with a scanning electron microscope, as shown in Examples described later.
本発明の正極用複合材料を用いた電池の用途は、特に限定されないが、例えばノートパソコン、電子ブックプレーヤー、ＤＶＤプレーヤー、携帯オーディオプレーヤー、ビデオムービー、携帯テレビ、携帯電話などの電子機器に使用できるほか、コードレス掃除機やコードレス電動工具、電気自動車、ハイブリッドカーなどのバッテリー、燃料電池車の補助電源などの民生用機器に使用できる。このうち特に高出力が求められる自動車用バッテリーとして好適に用いられる。 The use of the battery using the positive electrode composite material of the present invention is not particularly limited, but can be used for electronic devices such as notebook computers, electronic book players, DVD players, portable audio players, video movies, portable TVs, and mobile phones. In addition, it can be used for consumer devices such as cordless vacuum cleaners, cordless electric tools, batteries for electric vehicles, hybrid cars, etc., and auxiliary power sources for fuel cell vehicles. Among these, it is suitably used as a battery for automobiles that require particularly high output.
以下、本発明を具体的に示す実施例等について説明する。なお、実施例等における評価項目は下記のようにして測定を行った。 Examples and the like specifically showing the present invention will be described below. In addition, the evaluation item in an Example etc. measured as follows.
（１）ＤＢＰ吸収量
ＤＢＰ吸収量は、ＪＩＳ Ｋ ６２１７−４に基づいて測定した。
(1) DBP absorption amount DBP absorption amount was measured based on JIS K 6217-4.
（２）平均凝集粒径
レーザー回折／散乱式粒度分布測定装置ＬＡ９２０（堀場製作所製）を用い、水を分散媒とし、超音波３分照射後の粒度分布を相対屈折率１．５で測定したときの体積中位粒径（Ｄ５０）の値を繊維状炭素、カーボンブラックの平均凝集粒径、正極活物質、工程２における造粒物、及び工程３を経て得られた複合粒子の平均凝集粒径とした。
(2) Average agglomerated particle size Using a laser diffraction / scattering particle size distribution measuring apparatus LA920 (manufactured by Horiba, Ltd.), the particle size distribution after irradiation with ultrasonic waves for 3 minutes was measured at a relative refractive index of 1.5 using water as a dispersion medium. When the volume median particle size (D50) is the value, the average aggregate particle size of fibrous carbon, carbon black, the positive electrode active material, the granulated product in step 2, and the average aggregate particle of composite particles obtained through step 3 The diameter.
（３）カーボンブラックの一次粒径
電界放出形走査電子顕微鏡（日立製Ｓ−４０００）により撮影した倍率１００００〜５００００倍のＳＥＭ像から、一次粒子５０個を抽出し、それらの直径の平均値を一次粒子径とした。ただし、前記直径とは、（長軸径＋短軸径）／２で算出される値で、着目するカーボンブラックのＳＥＭ像を２本の平行線ではさんだ時、その２本の平行線の間隔が最小となるときの間隔を短軸径、この平行線に直角な方向の２本の平行線でこのカーボンブラックのＳＥＭ像をはさんだ時、その２本の平行線の間隔を長軸径とする。
(3) Primary particle diameter of carbon black 50 primary particles were extracted from an SEM image with a magnification of 10,000 to 50,000 times taken with a field emission scanning electron microscope (S-4000 manufactured by Hitachi), and the average value of their diameters was calculated. The primary particle size was used. However, the diameter is a value calculated by (major axis diameter + minor axis diameter) / 2, and when the SEM image of the carbon black of interest is sandwiched between two parallel lines, the distance between the two parallel lines When the SEM image of this carbon black is sandwiched between two parallel lines perpendicular to the parallel line, the distance between the two parallel lines is defined as the major axis diameter. To do.
（４）繊維状炭素の繊維径および繊維長さ
電界放出形走査電子顕微鏡（日立製Ｓ−４０００）により撮影した倍率２０００〜５００００倍のＳＥＭ像から、繊維状炭素３０個を抽出し、以下のように測定した線分の長さの平均値を繊維径とし、繊維の長さの平均値を繊維長とした。ここで、前記線分の長さとは、３０個の繊維状炭素のそれぞれについて、繊維状炭素の画像の長さ方向の輪郭が描く２本の曲線の一方の曲線の法線が、これら２本の曲線に切り取られる線分の長さをいう。
(4) Fiber diameter and fiber length of fibrous carbon 30 fibrous carbons were extracted from an SEM image with a magnification of 2000 to 50000 times taken with a field emission scanning electron microscope (S-4000 manufactured by Hitachi). The average value of the lengths of the measured line segments was defined as the fiber diameter, and the average value of the fiber lengths was defined as the fiber length. Here, the length of the line segment means that for each of the 30 fibrous carbons, the normal line of one of the two curves drawn by the contour in the length direction of the fibrous carbon image is the two normal lines. This is the length of the line segment cut out by the curve.
（５）繊維状炭素のアスペクト比
繊維状炭素の繊維長を繊維径で除することで求めた。
(5) Aspect ratio of fibrous carbon It was determined by dividing the fiber length of fibrous carbon by the fiber diameter.
（６）体積抵抗
ＪＩＳ Ｋ １４６９の方法において、粉体試料量を０．３ｇ、粉体圧縮時圧力を１００ｋｇ／ｃｍ２に変更して、円筒状に圧縮した圧縮粉体試料の電気抵抗値を測定し、測定抵抗値より下記の式１により体積抵抗率（電気抵抗率）を算出した。具体的には、絶縁性円筒（ベークライト製、外径２８ｍｍ、内径８ｍｍ）と（−）電極からなる円筒容器に粉体試料を０．３ｇ充填し、試料を詰めた絶縁性円筒容器に（＋）電極を挿入して粉体試料を挟み、プレス機架台上に設置した。プレス機により円筒容器内の試料に１００ｋｇ／ｃｍ２の力を加え、圧縮した。（＋）電極と（−）電極をデジタルマルチメーターの測定用入力ケーブルに接続し、圧縮開始から３分経過後、電気抵抗値を測定した。
(6) Volume resistance In the method of JIS K 1469, the amount of powder sample was changed to 0.3 g, the pressure at the time of powder compression was changed to 100 kg / cm 2, and the electric resistance value of the compressed powder sample compressed into a cylindrical shape was The volume resistivity (electrical resistivity) was calculated from the measured resistance value according to the following formula 1. Specifically, 0.3 g of a powder sample is filled in a cylindrical container composed of an insulating cylinder (made of Bakelite, outer diameter 28 mm, inner diameter 8 mm) and (−) electrode, and the insulating cylindrical container packed with the sample (+ ) The electrode was inserted and the powder sample was sandwiched, and placed on the press machine base. A force of 100 kg / cm 2 was applied to the sample in the cylindrical container by a press machine and compressed. The (+) electrode and the (−) electrode were connected to the input cable for measurement of a digital multimeter, and the electrical resistance value was measured after 3 minutes from the start of compression.
ρ＝Ｓ／ｈ×Ｒ （式１）
ここで、ρは電気抵抗率（Ω・ｃｍ）、Ｓは試料の断面積（ｃｍ２）、ｈは試料の充填高さ（ｃｍ）、Ｒは電気抵抗値（Ω）である。
ρ = S / h × R (Formula 1)
Here, ρ is the electrical resistivity (Ω · cm), S is the cross-sectional area (cm 2 ) of the sample, h is the filling height (cm) of the sample, and R is the electrical resistance value (Ω).
用いた（−）電極は、電池グレードの黄銅製であり、電極面は７．８±１ｍｍφで、高さ５ｍｍの突起部のある台座状電極であり、（＋）電極は、電池グレードの黄銅製であり、電極面は７．８±１ｍｍφで、長さ６０ｍｍの棒状電極であった。 The (−) electrode used was made of battery grade brass, the electrode surface was 7.8 ± 1 mmφ, and was a pedestal electrode with a protrusion of 5 mm in height, and the (+) electrode was a battery grade yellow It was made of copper, and the electrode surface was a rod-shaped electrode having a length of 7.8 ± 1 mmφ and a length of 60 mm.
（７）細孔容量
水銀圧入式細孔分布測定装置（ポアサイザー９３２０、島津製作所製）を用いて、０．０１〜１μｍの範囲の細孔容量の合計を測定し、得られた値を細孔容量とした。
(7) Pore volume Using a mercury intrusion pore distribution measuring device (pore sizer 9320, manufactured by Shimadzu Corporation), the total pore volume in the range of 0.01 to 1 μm was measured, and the obtained value was assigned to the pore. The capacity.
（８）溶媒中での分散状態の確認方法
レーザー回折／散乱式粒度分布測定装置ＬＡ９２０（堀場製作所製）に、スラリーと同一の溶媒１２０ｍＬを添加し、攪拌循環（循環レベル４）させた。そこに、サンプリングしたスラリー（溶媒中に正極活物質粒子と繊維状炭素とを含有するスラリー）を滴下し、装置のセル内のレーザーの透過率が７５％〜９５％の範囲になるようスラリー濃度を調節した。そして、装置のメモリ７で超音波３分照射後の粒度分布を相対屈折率１．５で測定し、このときの体積中位粒径（Ｄ５０）を上記（２）の条件で測定した正極活物質の平均凝集粒径で除して、これに１００を乗じて比率を算出した。本発明では、この比率が１３０％以内になるような状態を分散状態とする。
(8) Method for Confirming Dispersion State in Solvent 120 mL of the same solvent as the slurry was added to a laser diffraction / scattering particle size distribution measuring apparatus LA920 (manufactured by Horiba Seisakusho) and stirred and circulated (circulation level 4). The sampled slurry (slurry containing positive electrode active material particles and fibrous carbon in a solvent) is dropped therein, and the slurry concentration is set so that the laser transmittance in the cell of the apparatus is in the range of 75% to 95%. Adjusted. Then, the particle size distribution after irradiation with ultrasonic waves for 3 minutes was measured with a relative refractive index of 1.5 in the memory 7 of the apparatus, and the volume median particle size (D50) at this time was measured under the condition (2) above. The ratio was calculated by dividing this by the average agglomerated particle size of the substance and multiplying this by 100. In the present invention, a state in which this ratio is within 130% is defined as a dispersed state.
（９）正極活物質粒子が繊維状炭素により保持されている状態の確認方法
正極活物質と繊維状炭素とを有する一粒の複合粒子を、６００℃１時間加熱したとき、当該一粒の複合粒子が、複数の複合粒子に崩壊するか、又は繊維状炭素がほぼ消失した正極活物質粒子に崩壊した場合、当該一粒の複合粒子中の正極活物質粒子は繊維状炭素により保持されていたものとする。すなわち、６００℃１時間加熱した複合粒子を電界放出形走査電子顕微鏡（日立製S-4000）により撮影し、倍率1000〜50000倍のSEM画像を目視観察する。観察の結果、繊維状炭素がほぼ消失した正極活物質粒子のみ観察される場合、正極活物質粒子に繊維状炭素が絡んだ複合粒子のみ観察される場合、さらには、繊維状炭素がほぼ消失した正極活物質粒子と正極活物質粒子に繊維状炭素が絡んだ複合粒子の両方が観察される場合を正極活物質粒子が繊維状炭素により保持されていたものとする。一方、繊維状炭素がほぼ消失した正極活物質粒子と凝集した繊維状炭素の粒子が観察される場合、正極活物質粒子が繊維状炭素により保持されていなかったものとする。
(9) Method for confirming state in which positive electrode active material particles are held by fibrous carbon When a single composite particle having a positive electrode active material and fibrous carbon is heated at 600 ° C. for 1 hour, the single composite particle When the particles collapsed into a plurality of composite particles, or the cathode active material particles in which the fibrous carbon almost disappeared, the cathode active material particles in the one composite particle were held by the fibrous carbon. Shall. That is, the composite particles heated at 600 ° C. for 1 hour are photographed with a field emission scanning electron microscope (Hitachi S-4000), and SEM images with a magnification of 1000 to 50000 times are visually observed. As a result of observation, when only the positive electrode active material particles in which the fibrous carbon substantially disappears are observed, when only the composite particles in which the fibrous carbon is entangled with the positive electrode active material particles are observed, the fibrous carbon has almost disappeared. The case where both the positive electrode active material particles and the composite particles in which fibrous carbon is entangled with the positive electrode active material particles is observed is assumed to be held by the fibrous carbon. On the other hand, when positive electrode active material particles in which fibrous carbon has substantially disappeared and aggregated fibrous carbon particles are observed, it is assumed that the positive electrode active material particles are not retained by the fibrous carbon.
（１０）電池の作製
表２に示す配合比にて正極用複合材料、カーボンブラック、１２重量％ポリフッ化ビニリデン（ＰＶＤＦ）のＮメチルピロリドン溶液、Ｎメチルピロリドンを均一に混合し、塗工用ペーストを調製した。当該ペーストをコーター（ＹＢＡ型ベーカーアプリケーター）にて集電体として用いたアルミニウム箔（厚さ２０μｍ）上に均一に塗工（乾燥後に０．００９ｇ／ｃｍ２）し、８０℃にて１２時間以上かけて減圧（１００〜３００ｍｍＨｇ）乾燥した。乾燥後、所定の大きさ（２０ｍｍ×１５ｍｍ）に切断し、アルミニウム箔を含む全体の厚さが５５μｍになるようにプレス機で均一膜厚に成型して、試験用正極とした。
(10) Preparation of battery The composite material for positive electrode, carbon black, 12% by weight polyvinylidene fluoride (PVDF) N-methylpyrrolidone solution and N-methylpyrrolidone were uniformly mixed at the mixing ratio shown in Table 2, and the coating paste Was prepared. The paste was uniformly coated (0.009 g / cm 2 after drying) on an aluminum foil (thickness 20 μm) used as a current collector with a coater (YBA-type baker applicator), and at 80 ° C. for 12 hours or more And dried under reduced pressure (100 to 300 mmHg). After drying, it was cut into a predetermined size (20 mm × 15 mm), and formed into a uniform film thickness with a press so that the total thickness including the aluminum foil was 55 μm, to obtain a test positive electrode.
ハードカーボン１０重量部、１２重量％ポリフッ化ビニリデン（ＰＶＤＦ）のＮメチルピロリドン溶液９．３重量部、Ｎメチルピロリドン８．５重量部を均一に混合し、塗工用ペーストを調製した。当該ペーストをコーター（ＹＢＡ型ベーカーアプリケーター）にて集電体として用いた銅箔（厚さ１８μｍ）上に均一に塗工し、８０℃にて１２時間以上かけて減圧（１００〜３００ｍｍＨｇ）乾燥した。乾燥後、所定の大きさ（２０ｍｍ×１５ｍｍ）に切断し、プレス機で均一膜厚に成型して、試験用負極とした。このときの負極層の厚さは２５μｍとした。セパレータはセルガード＃２４００（セルガード製）を使用した。電解液は、１ｍｏｌ／ＬのＬｉＰＦ６のエチレンカーボネート：ジエチルカーボネート（１：１ｖｏｌ％）溶液を用いた。試験セルの組み立てはアルゴン雰囲気下のグローブボックス内で行った。試験セルの組み立て後、２５℃にて２４時間放置後、内部抵抗特性評価を行った。 10 parts by weight of hard carbon, 9.3 parts by weight of 12% by weight polyvinylidene fluoride (PVDF) in N-methylpyrrolidone and 8.5 parts by weight of N-methylpyrrolidone were uniformly mixed to prepare a coating paste. The paste was uniformly coated on a copper foil (thickness 18 μm) used as a current collector with a coater (YBA type baker applicator), and dried under reduced pressure (100 to 300 mmHg) at 80 ° C. over 12 hours. . After drying, it was cut into a predetermined size (20 mm × 15 mm) and molded into a uniform film thickness with a press machine to obtain a test negative electrode. The thickness of the negative electrode layer at this time was 25 μm. As the separator, Celgard # 2400 (manufactured by Celgard) was used. As the electrolytic solution, an ethylene carbonate: diethyl carbonate (1: 1 vol%) solution of 1 mol / L LiPF 6 was used. The test cell was assembled in a glove box under an argon atmosphere. After the test cell was assembled, it was left at 25 ° C. for 24 hours, and then the internal resistance characteristics were evaluated.
（１１）内部抵抗特性評価
後述する実施例３，４および比較例１により得られたリチウムイオン二次電池の内部抵抗を評価した。まず、０．２Ｃの定電流で４．０Ｖまで充電した後、４．０Ｖで定電位充電を１時間行うことにより、各電池を満充電の約６０％の充電状態に調整した。そして、５Ｃの定電流値で３０秒間放電を行い、電位降下値を測定した。この電位降下値を放電電流値で除した値を電池の内部抵抗値として、得られたリチウムイオン二次電池の内部抵抗を評価した。表２には比較例１の内部抵抗値を１００とした場合の実施例３，４の内部抵抗値の相対値を示す。
(11) Evaluation of internal resistance characteristics The internal resistance of the lithium ion secondary batteries obtained in Examples 3 and 4 and Comparative Example 1 described later were evaluated. First, after charging to 4.0 V with a constant current of 0.2 C, constant potential charging was performed at 4.0 V for 1 hour, thereby adjusting each battery to a charged state of about 60% of full charge. Then, discharging was performed at a constant current value of 5 C for 30 seconds, and a potential drop value was measured. The internal resistance of the obtained lithium ion secondary battery was evaluated using a value obtained by dividing the potential drop value by the discharge current value as the internal resistance value of the battery. Table 2 shows the relative values of the internal resistance values of Examples 3 and 4 when the internal resistance value of Comparative Example 1 is 100.
実施例１
水１００重量部にフェニル基を官能基にもつノニオン型分散剤（花王製エマルゲンＡ−９０）を０．３７５重量部添加し溶解させた。その溶液に繊維径２０ｎｍ、繊維長５μｍ、アスペクト比２５０のカーボンナノチューブを０．３７５重量部添加し、カーボンナノチューブの平均凝集粒径が３μｍになるまで超音波分散した。このカーボンナノチューブ分散液に超音波を照射しながら、平均凝集粒径２μｍ（一次粒子径２５ｎｍ）、ＤＢＰ吸収量１５５ｃｍ３／１００ｇのカーボンブラックを０．１５重量部添加し１分間超音波照射した後、平均凝集粒径１．２μｍのマンガン酸リチウム７．５重量部を添加し、更に超音波による分散を２分行った。得られた分散液を噴霧乾燥機（東京理化器械製ＳＤ−１０００）を用いて熱風温度１３５℃で噴霧乾燥した。得られた顆粒６ｇを円筒ろ紙にいれ、ソックスレー抽出機で、４００ｍｌのエタノールにより、８時間抽出し、顆粒に残留している分散剤を除去した。得られた正極用複合材料を図１に、物性を表１に示す。得られた正極用複合材料は、上記（９）に示す方法で確認したところ、正極活物質粒子がカーボンナノチューブにより保持された複合粒子であり、より詳細には、図１に示すように、カーボンナノチューブが正極活物質粒子間隙に存在するとともに、カーボンナノチューブが正極活物質粒子を網目状に包み込んだ形態を有していた。
Example 1
0.375 parts by weight of a nonionic dispersant having a phenyl group as a functional group (Emulgen A-90 manufactured by Kao) was added to 100 parts by weight of water and dissolved. 0.375 parts by weight of carbon nanotubes having a fiber diameter of 20 nm, a fiber length of 5 μm, and an aspect ratio of 250 were added to the solution, and ultrasonically dispersed until the average aggregate particle diameter of the carbon nanotubes reached 3 μm. While irradiating ultrasonic waves to the carbon nanotube dispersion liquid, the average aggregate particle size 2 [mu] m (primary particle size 25 nm), after ultrasonic irradiation of carbon black DBP absorption 155cm 3 / 100g 0.15 parts by weight added to 1 minute Then, 7.5 parts by weight of lithium manganate having an average agglomerated particle size of 1.2 μm was added, and further ultrasonic dispersion was performed for 2 minutes. The obtained dispersion was spray-dried at a hot air temperature of 135 ° C. using a spray dryer (Tokyo Rika Kikai SD-1000). 6 g of the obtained granule was put into a cylindrical filter paper, and extracted with 400 ml of ethanol for 8 hours with a Soxhlet extractor to remove the dispersant remaining in the granule. The obtained composite material for positive electrode is shown in FIG. The obtained composite material for positive electrode was confirmed by the method shown in (9) above. As a result, the positive electrode active material particles were composite particles held by carbon nanotubes. More specifically, as shown in FIG. The nanotubes existed in the gaps between the positive electrode active material particles, and the carbon nanotubes had a form in which the positive electrode active material particles were wrapped in a network.
実施例２
実施例１と同じ要領で噴霧乾燥して得た、分散剤が含有した顆粒１．５ｇを電気炉で２００℃、１０時間加熱し、分散剤を分解気化させ除去した。得られた正極用複合材料を図２に、物性を表１に示す。得られた正極用複合材料は、上記（９）に示す方法で確認したところ、正極活物質粒子がカーボンナノチューブにより保持された複合粒子であり、より詳細には、図２に示すように、カーボンナノチューブが正極活物質粒子間隙に存在するとともに、カーボンナノチューブが正極活物質粒子を網目状に包み込んだ形態を有していた。
Example 2
1.5 g of granules containing the dispersant obtained by spray-drying in the same manner as in Example 1 were heated in an electric furnace at 200 ° C. for 10 hours to decompose and remove the dispersant. The obtained composite material for positive electrode is shown in FIG. The obtained composite material for positive electrode was confirmed by the method shown in the above (9). As a result, the positive electrode active material particles were composite particles held by carbon nanotubes. More specifically, as shown in FIG. The nanotubes existed in the gaps between the positive electrode active material particles, and the carbon nanotubes had a form in which the positive electrode active material particles were wrapped in a network.
実施例３
フェニル基を官能基にもつノニオン型分散剤の使用量を０．１５重量部、カーボンナノチューブの使用量を０．１５重量部にしたこと以外は、実施例１と同じ手法で正極用複合材料を得た。得られた正極用複合材料を図３に、物性を表１、電池作製時の内部抵抗を表２に示す。得られた正極用複合材料は、上記（９）に示す方法で確認したところ、正極活物質粒子がカーボンナノチューブにより保持された複合粒子であり、より詳細には、図３に示すように、カーボンナノチューブが正極活物質粒子間隙に存在するとともに、カーボンナノチューブが正極活物質粒子を網目状に包み込んだ形態を有していた。
Example 3
The composite material for positive electrode was prepared in the same manner as in Example 1 except that the amount of nonionic dispersant having a phenyl group as a functional group was 0.15 parts by weight and the amount of carbon nanotubes was 0.15 parts by weight. Obtained. The obtained composite material for positive electrode is shown in FIG. 3, the physical properties are shown in Table 1, and the internal resistance during battery production is shown in Table 2. The obtained composite material for positive electrode was confirmed by the method shown in (9) above. As a result, positive electrode active material particles were composite particles held by carbon nanotubes. More specifically, as shown in FIG. The nanotubes existed in the gaps between the positive electrode active material particles, and the carbon nanotubes had a form in which the positive electrode active material particles were wrapped in a network.
実施例４
カーボンナノチューブの代わりに、繊維径１２０ｎｍ、繊維長１０μｍ、アスペクト比８３のＶＧＣＦ（０．２２５重量部）を用い、分散剤の使用量を０．２２５重量部としたこと以外は、実施例１と同じ手法により正極用複合材料を得た。得られた正極用複合材料を図４に、物性を表１、電池作製時の内部抵抗を表２に示す。得られた正極用複合材料は、上記（９）に示す方法で確認したところ、正極活物質粒子がＶＧＣＦにより保持された複合粒子であり、より詳細には、図４に示すように、ＶＧＣＦが正極活物質粒子間隙に存在するとともに、ＶＧＣＦが正極活物質粒子を網目状に包み込んだ形態を有していた。
Example 4
Example 1 except that VGCF (0.225 parts by weight) having a fiber diameter of 120 nm, a fiber length of 10 μm, and an aspect ratio of 83 was used instead of the carbon nanotubes, and the amount of the dispersant used was 0.225 parts by weight. The composite material for positive electrodes was obtained by the same method. FIG. 4 shows the obtained composite material for positive electrode, Table 1 shows the physical properties, and Table 2 shows the internal resistance during battery production. The obtained composite material for positive electrode was confirmed by the method shown in (9) above. As a result, the positive electrode active material particles were composite particles held by VGCF. In more detail, as shown in FIG. In addition to being present in the gaps between the positive electrode active material particles, the VGCF had a form in which the positive electrode active material particles were wrapped in a network.
比較例１
実施例１において、カーボンナノチューブ０．３７５重量部を使用する代わりに、カーボンブラック０．３７５重量部を使用することで、カーボンブラックの合計量を０．５２５重量部としたこと以外は、実施例１と同じ手法により正極用複合材料を得た。得られた正極用複合材料の物性を表１、電池作製時の内部抵抗を表２に示す。
Comparative Example 1
In Example 1, instead of using 0.375 parts by weight of carbon nanotubes, 0.375 parts by weight of carbon black was used, except that the total amount of carbon black was 0.525 parts by weight. 1 was used to obtain a composite material for positive electrode. Table 1 shows the physical properties of the obtained composite material for positive electrode, and Table 2 shows the internal resistance during battery production.
比較例２
実施例１において、分散剤を加えずに、同量のカーボンナノチューブ、カーボンブラック、及びマンガン酸リチウムをマグネチックスターラーにより混合して、スラリーを調製したこと以外は、実施例１と同じ手法により正極用複合材料を得た。得られた正極用複合材料の物性を表１に示す。なお、実施例１〜４では、噴霧乾燥前の分散液の状態について、上記（８）に示す方法で求めた比率が何れも１３０％以内であったが、この比較例２では、当該比率が４００％であり、分散状態とはいえなかった。また、比較例２の正極用複合材料は、上記（９）に示す方法で確認したところ、一粒の複合粒子が、繊維状炭素がほぼ消失した正極活物質粒子と凝集した繊維状炭素の粒子とに崩壊したため、正極活物質粒子が繊維状炭素（カーボンナノチューブ）により保持された複合粒子ではなかった。
Comparative Example 2
In Example 1, the same amount of carbon nanotubes, carbon black, and lithium manganate were mixed with a magnetic stirrer without adding a dispersant, and a slurry was prepared. A composite material was obtained. Table 1 shows the physical properties of the obtained composite material for positive electrode. In Examples 1 to 4, the ratios obtained by the method shown in (8) above were within 130% for the state of the dispersion before spray drying, but in Comparative Example 2, the ratio was It was 400% and could not be said to be in a dispersed state. Further, the composite material for positive electrode of Comparative Example 2 was confirmed by the method shown in (9) above. As a result, one composite particle was composed of positive carbon active material particles in which fibrous carbon almost disappeared and aggregated fibrous carbon particles. Therefore, the positive electrode active material particles were not composite particles held by fibrous carbon (carbon nanotubes).
表１の結果が示すように、実施例１〜４のリチウム電池正極用複合材料は、体積抵抗が小さく、細孔容量も十分であるため、電池の放電時にリチウムイオンの移動がスムーズになると考えられる。また、表２の結果が示すように、電池作製時の特性として、その内部抵抗をより小さくすることができた。 As the results in Table 1 show, the lithium battery positive electrode composite materials of Examples 1 to 4 have a small volume resistance and a sufficient pore capacity, so that the lithium ions move smoothly during battery discharge. It is done. Moreover, as the result of Table 2 shows, the internal resistance was able to be made smaller as a characteristic at the time of battery preparation.
一方、繊維状炭素を使用せずに得られたリチウム電池正極用複合材料（比較例１）では、体積抵抗が大きく、細孔容量も不十分であり、電池作製時の内部抵抗も大きい値となった。また、繊維状炭素の分散が不十分なスラリーを使用して噴霧造粒により得られたリチウム電池正極用複合材料（比較例２）では、体積抵抗が大きかった。 On the other hand, the composite material for a lithium battery positive electrode (Comparative Example 1) obtained without using fibrous carbon has a large volume resistance, insufficient pore capacity, and a large internal resistance during battery production. became. In addition, the lithium battery positive electrode composite material (Comparative Example 2) obtained by spray granulation using a slurry with insufficient fibrous carbon dispersion had a large volume resistance.
Claims (10)
［工程１］溶媒中に正極活物質粒子と繊維状炭素とが分散した状態で含まれるスラリーを得る工程、
［工程２］前記工程１で得たスラリーを噴霧造粒して、前記正極活物質粒子と前記繊維状炭素とを含有する造粒物を得る工程。 The manufacturing method of the composite material for lithium battery positive electrodes comprised from the composite particle containing the positive electrode active material particle and fibrous carbon including the following processes 1 and 2.
[Step 1] A step of obtaining a slurry containing positive electrode active material particles and fibrous carbon dispersed in a solvent,
[Step 2] A step of spray granulating the slurry obtained in Step 1 to obtain a granulated product containing the positive electrode active material particles and the fibrous carbon.
［工程３］前記造粒物から前記分散剤を除去して複合粒子を得る工程。 Furthermore, the manufacturing method of the composite material for lithium battery positive electrodes of Claim 2 or 3 including the following processes 3 in the said process 2 or after the said process 2. FIG.
[Step 3] A step of removing the dispersant from the granulated material to obtain composite particles.
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| JP2017201006A (en) * | 2016-04-28 | 2017-11-09 | 株式会社ＤＲ．ｇｏｏ | Method for producing granule of carbon having different bulk density and granule of carbon obtained by the same |
| JP7457227B1 (en) | 2023-06-30 | 2024-03-28 | ａｒｔｉｅｎｃｅ株式会社 | Secondary battery electrode composite |
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