JP2004220909A - Positive electrode activator and positive electrode using the same, lithium ion battery and lithium polymer battery using positive electrode - Google Patents

Positive electrode activator and positive electrode using the same, lithium ion battery and lithium polymer battery using positive electrode Download PDF

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JP2004220909A
JP2004220909A JP2003006636A JP2003006636A JP2004220909A JP 2004220909 A JP2004220909 A JP 2004220909A JP 2003006636 A JP2003006636 A JP 2003006636A JP 2003006636 A JP2003006636 A JP 2003006636A JP 2004220909 A JP2004220909 A JP 2004220909A
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positive electrode
carbon
active material
graphite
conductive additive
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Yusuke Watarai
祐介 渡会
Akio Mizuguchi
暁夫 水口
Hiroyuki Imai
浩之 今井
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Mitsubishi Materials Corp
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Mitsubishi Materials Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode activator restraining the lowering of the energy density of a battery, capable of improving output characteristics. <P>SOLUTION: The positive electrode activator contains grain-shaped lithium-containing transition metal oxide 11 with average grain size of 3 μm to 40 μm, and a conductive additive material 14 composed of carbon nanofiber 13 as main component constructed by laminating a plurality of flat-shaped graphite nets 12 with average diameter of 10 nm to 500 nm which is substantially perpendicular to the vertical axis of the fiber. The carbon nanofiber 13 contained in the conductive additive material 14 has a length of not less than 1,000 nm and an aspect ratio of not less than 10. The content of the conductive additive material 14 to the total weight of the activator is 0.5 wt.% to 15 wt.%. In addition to the carbon nanofiber, the conductive additive material of the positive electrode activator contains grain-shaped aggregates 16 composed of carbon fine powder having graphite structure. The content of the carbon nanofiber is 80 to 99.5 wt.% and that of the grain-shaped aggregate is 0.5 to 20 wt.%. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、電池のエネルギ密度の低下を抑制し、出力特性の向上が可能になる、正極活物質及びこれを用いた正極、並びにこの正極を用いたリチウムイオン電池及びリチウムポリマー電池に関する。
【０００２】
【従来の技術】
近年、携帯電話やノート型パソコン等のポータブル電子機器の発達や、電気自動車の実用化等に伴い、小型軽量でかつ高容量の二次電池が必要とされるようになってきた。現在、この要求に応える高容量二次電池として、正極材料としてＬｉＣｏＯ２等のリチウム含有遷移金属酸化物を用い、負極活物質として炭素系材料を用いたリチウムイオン二次電池が商品化されている。上記リチウムイオン二次電池は、エネルギ密度が高く、かつ小型、軽量化が図れることから、ポータブル電子機器の電源として注目されている。
正極活物質の電子伝導性はさほど高くなく半導体に属するものが多いので、電極の導電性を確保するため、導電剤を加えて結着剤を用いて正極合剤を作製する。従来、導電剤にはカーボン、アセチレンブラック、グラファイト等が用いられている。電池の高率放電特性を高めるには、正極中の導電剤の割合を高めることでその特性が得られるが、多量の導電剤の含有は、リチウム含有遷移金属酸化物の含有割合を低下させるため、放電容量が減少する問題を生じる。
【０００３】
上記問題点を解決する技術として、正極活物質と導電剤とバインダを備えた合剤層が金属の基材に形成されてなる正極と、負極と有機電解質よりなり、該正極活物質がマンガンを主体とするリチウム複合酸化物である有機電解質電池において、該導電剤がカーボンナノチューブである有機電解質電池が開示されている（例えば特許文献１参照。）。このカーボンナノチューブを導電剤として使用した有機電解質電池は、正極活物質同士の導電性を改良でき、高率放特性や充放電サイクル特性に優れた有機電解質電池を実現することができる。
また、含リチウム複合酸化物を正極活物質とし、導電助剤として平均粒径が１００ｎｍ以下の非晶質炭素材料と平均粒径が１〜１０μｍの黒鉛系炭素材料とを用いた非水二次電池用正極も開示されている（例えば、特許文献２参照。）。この導電助剤に用いられている平均粒径１００μｍの非晶質炭素材料には、アセチレンブラック、ケッチェンブラックのようなカーボンブラック、気相成長炭素繊維、カーボンナノチューブ、ピッチを紡糸して炭化処理した炭化繊維等が用いられる。平均粒径１００μｍの非晶質炭素材料の粒子を用いることにより、活物質粒子の間隙に入り込みやすく、充填性を高められるので、４．５Ｖ以上の高い作動電圧を有する材料を正極活物質として用いた場合でも、サイクル特性及び付加特性が優れる。
【０００４】
【特許文献１】
特開平１１−２８３６２９号公報
【特許文献２】
特開２００２−２７９９９８号公報
【０００５】
【発明が解決しようとする課題】
しかし、上記特許文献１及び特許文献２に示された電池では、正極の導電性を得るために導電剤として粒径の小さい炭素材料やカーボンナノチューブ等が用いられているが、図８に示すように、カーボンナノチューブはグラファイト網面が繊維軸に平行に配向しているため、軸方向に平行に導電し易い。従って、従来より導電剤として用いられてきたカーボン、アセチレンブラック、グラファイト等と大差ない導電性しか得られず、リチウム含有遷移金属酸化物同士の導電性を十分に高めることができていない問題があった。
本発明の目的は、電池のエネルギ密度の低下を抑制し、出力特性の向上が可能になる、正極活物質及びこれを用いた正極、並びにこの正極を用いたリチウムイオン電池及びリチウムポリマー電池を提供することにある。
【０００６】
【課題を解決するための手段】
請求項１に係る発明は、図１に示すように、平均粒径３μｍ〜４０μｍの粒子状のリチウム含有遷移金属酸化物１１と平均直径１０ｎｍ〜５００ｎｍの平面状のグラファイト網１２が複数積層され、グラファイト網がファイバの縦軸に対して実質的に垂直であるカーボンナノファイバ１３を主成分とする導電性添加材料１４をそれぞれ含み、この導電性添加材料１４に含まれるカーボンナノファイバ１３が１０００ｎｍ以上の長さと、１０以上のアスペクト比を有し、導電性添加材料１４が活物質全体重量に対して０．５重量％〜１５重量％であることを特徴とする正極活物質である。
請求項１に係る発明では、本発明の正極活物質を用いて電池の電極を作製した場合、粒子状のリチウム含有遷移金属酸化物１１が形成する空隙に平均直径１０ｎｍ〜５００ｎｍの平面状のグラファイト網１２が複数積層されて形成されたカーボンナノファイバ１３を主成分とする導電性添加材料１４が充填されることで導電性が高まり、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。
また、図３に示すように、本発明の導電性添加材料１４の主成分である１０００ｎｍ以上の長さと、１０以上のアスペクト比を有するカーボンナノファイバ１３はグラファイト網１２が複数積層された構造を持ち、繊維軸に垂直に配向しており、軸方向に垂直に導電し易い。従って、従来の炭素材料やカーボンナノチューブを添加する場合に比べて少量の添加で導電性が大幅に高まる。
【０００７】
請求項２に係る発明は、請求項１に係る発明であって、図４に示すように、導電性添加材料１４はカーボンナノファイバ１３に加えて、更に黒鉛構造を有する炭素微粉からなる粒子状凝集体１６を含み、カーボンナノファイバ１３が８０重量％〜９９．５重量％、粒子状凝集体１６が０．５重量％〜２０重量％の割合である正極活物質である。
請求項２に係る発明では、導電性添加材料１４に粒子状凝集体１６を含むことによって主成分であるカーボンナノファイバ１３同士の接触が良好になり、高率充放電特性が更に向上する。
【０００８】
請求項３に係る発明は、請求項１又は２に係る発明であって、導電性添加材料１４に含まれるカーボンナノファイバ又は、カーボンナノファイバ及び粒子状凝集体をそれぞれ含む混合物のＸ線回折において測定されるグラファイト網１２平面の積層間隔ｄ００２が０．３３５４ｎｍ〜０．３３９ｎｍである正極活物質である。
請求項４に係る発明は、請求項１ないし３いずれか１項に係る発明であって、導電性添加材料１４に平均粒径１０ｎｍ〜５００ｎｍの金属又は金属酸化物１７のどちらか一方又はその双方を０．５重量％〜１０重量％更に含む正極活物質である。
請求項４に係る発明では、導電性添加材料１４に平均粒径１０ｎｍ〜５００ｎｍの金属又は金属酸化物１７を更に含ませることで、金属又は金属酸化物が電子伝導の基点となるため、より高率の放電が可能となる。
【０００９】
請求項５に係る発明は、請求項１ないし４いずれか１項に係る発明であって、カーボンナノファイバ１３の露出部又は、カーボンナノファイバ１３及び粒子状凝集体１６をそれぞれ含む混合物の露出部の少なくとも８５％がグラファイト網の端部である正極活物質である。
請求項６に係る発明は、請求項１ないし５いずれか１項に係る発明であって、金属又は金属酸化物のどちらか一方又はその双方がカーボンナノファイバの長軸上にある正極活物質である。
請求項７に係る発明は、請求項４又は６に係る発明であって、金属がＦｅ、Ｃｏ、Ｎｉ、Ｍｇ、Ａｌ及びＭｎからなる群より選ばれた少なくとも１種の元素である正極活物質である。
【００１０】
請求項８に係る発明は、請求項１に係る発明であって、粒子状のリチウム含有遷移金属酸化物１１がＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４からなる群より選ばれた少なくとも１種か、又はＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４の組成の一部を金属元素で置換した非化学量論的化合物からなる群より選ばれた少なくとも１種のどちらか一方又は双方を含む正極活物質である。
請求項９に係る発明は、請求項１ないし８いずれか１項に係る発明であって、導電性添加材料に粒子状の炭素系材料を更に含み、この炭素系材料が石炭、コークス、ポリアクリロニトリル系炭素繊維、ピッチ系炭素繊維、有機物の炭素化品、天然黒鉛、人造黒鉛、合成黒鉛、メソカーボンマイクロビーズ、有機物の黒鉛化品及び黒鉛繊維からなる群より選ばれた少なくとも１種を含む正極活物質である。
請求項９に係る発明では、粒子状の炭素系材料によってカーボンナノファイバ同士の接触が良好になり、高率充放電特性が更に向上する。また活物質の有効利用率が向上し、容量の増加に繋がる。
【００１１】
請求項１０に係る発明は、請求項１ないし９いずれか１項に記載の正極活物質と、バインダとを用いて形成された正極である。
この請求項１０に記載された正極では、グラファイト網が複数積層されて形成されたカーボンナノファイバが粒子状のリチウム含有遷移金属酸化物が形成する空隙に充填されることで導電性が高まり、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。
【００１２】
請求項１１に係る発明は、請求項１０記載の正極を用いて形成されたリチウムイオン電池である。
請求項１２に係る発明は、請求項１０記載の正極を用いて形成されたリチウムポリマー電池である。
この請求項１１又は１２に記載されたリチウムイオン電池又はリチウムポリマー電池では、グラファイト網が複数積層されて形成されたカーボンナノファイバが粒子状のリチウム含有遷移金属酸化物が形成する空隙に充填されることで導電性が高まり、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。また、従来より用いられてきた炭素材料に比べて、サイズの小さいカーボンナノファイバを用いているため、高密度での充電が可能となり、電池のエネルギ密度向上につながる。
【００１３】
【発明の実施の形態】
次に本発明の実施の形態を図面に基づいて説明する。
図１及び図２に示すように、リチウムイオン電池又はリチウムポリマー電池の正極は、平均粒径３μｍ〜４０μｍの粒子状のリチウム含有遷移金属酸化物１１と平均直径１０ｎｍ〜５００ｎｍの平面状のグラファイト網１２が複数積層され、グラファイト網がファイバの縦軸に対して実質的に垂直であるカーボンナノファイバ１３を主成分とする導電性添加材料１４をそれぞれ含む正極活物質が用いられる。導電性添加材料１４に含まれるカーボンナノファイバ１３は１０００ｎｍ以上の長さと、１０以上のアスペクト比を有するように構成される。平均直径が２０ｎｍ〜３００ｎｍ、長さが１０００ｎｍ〜６０００ｎｍ、アスペクト比が２０〜２００を有するように構成されることが好ましい。平均粒径の大きな粒子状のリチウム含有遷移金属酸化物１１とナノサイズの導電性添加材料１４をそれぞれ含む本発明の正極活物質を用いて電池の電極を作製した場合、リチウム含有遷移金属酸化物１１が形成する空隙に導電性添加材料１４が充填されるため、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。本発明の導電性添加材料１４の主成分である１０００ｎｍ以上の長さと、１０以上のアスペクト比を有するカーボンナノファイバ１３はグラファイト網１２が複数積層された構造を持つため、繊維軸に垂直に配向しており、軸方向に垂直に導電し易い。従って、従来の炭素材料やカーボンナノチューブを添加する場合に比べて少量の添加で導電性が大幅に高まる。また図５に示すように、グラファイト網１２のある端部１２ａの一辺が別のグラファイト網の端部の一辺と接合し、更に別の端部の一辺が更に別のグラファイト網の端部の一辺と接合して形成され、各辺から折り畳んだ構造を有するカーボンナノファイバ１３を用いてもよい。
【００１４】
本発明の正極活物質は導電性添加材料１４が活物質全体重量に対して０．５重量％〜１５重量％の割合で構成される。導電性添加材料１４は活物質全体重量に対して１重量％〜１０重量％の割合が好ましい。導電性添加材料１４の割合が活物質全体重量に対して０．５重量％未満の正極活物質を用いて正極を形成すると十分な導電性が得られず、容量が低く、出力特性も悪くなる不具合を生じ、導電性添加材料１４の割合が活物質全体重量に対して１５重量％を越える正極活物質を用いて正極を形成すると、電極中の活物質の割合が低下し、電極のエネルギー密度が低下する不具合を生じる。
【００１５】
また、グラファイト網１２の平均直径を１０ｎｍ〜５００ｎｍの範囲内とすることで最適な導電性向上効果が得られる。グラファイト網１２の平均直径が１０ｎｍ未満では隣接しているリチウム含有遷移金属酸化物同士の接触が十分に得られない不具合があり、５００ｎｍを越えるとリチウム含有遷移金属酸化物の空隙に収まり難くなる不具合を生じる。
また、カーボンナノファイバは従来より用いられてきた導電性添加材料に比べて、サイズの小さい材料であるため、電池の電極を作製した場合、高密度での充電が可能となり、電池のエネルギ密度向上につながる。
【００１６】
また本発明の導電性添加材料１４は、図４に示すように、カーボンナノファイバ１３に加えて、更に黒鉛構造を有する炭素微粉からなる粒子状凝集体１６を含む。導電性添加材料中のカーボンナノファイバ１３の含有量は８０重量％〜９９．５重量％、粒子状凝集体１６の含有量は０．５重量％〜２０重量％の割合である。好ましくはカーボンナノファイバ１３が９０重量％〜９９重量％、粒子状凝集体１６が１重量％〜１０重量％の割合である。カーボンナノファイバ１３の含有量を８０重量％〜９９．５重量％の範囲に限定したのは、８０重量％未満では導電性添加の効果が十分ではなく、９９．５重量％を越えるとカーボンナノファイバ同士の電気的接触が低下し、やはり導電性添加の効果が十分に得られないからである。
【００１７】
カーボンナノファイバ又は、カーボンナノファイバ及び粒子状凝集体をそれぞれ含む混合物をＸ線回折において測定したとき、得られるグラファイト網平面の積層間隔ｄ００２は０．３３５４ｎｍ〜０．３３９ｎｍの範囲内である。好ましい積層間隔ｄ００２は０．３３５４ｎｍ〜０．３３７ｎｍである。
図４に示すように、平均粒径１０ｎｍ〜５００ｎｍの金属又は金属酸化物１７のどちらか一方又はその双方を０．５重量％〜１０重量％更に含ませることにより、平均粒径１０ｎｍ〜５００ｎｍの金属又は金属酸化物１７が電子伝導の基点となるため、より高率の放電が可能となる。カーボンナノファイバ１３の露出部又は、カーボンナノファイバ１３及び粒子状凝集体１６をそれぞれ含む混合物の露出部の少なくとも８５％がグラファイト網の端部であることが好ましい。ここでグラファイト網の端部とは図２及び図５においては符号１２ａで表される箇所を示す。金属又は金属酸化物のどちらか一方又はその双方がカーボンナノファイバの長軸上に位置するように構成される。金属としてはＦｅ、Ｃｏ、Ｎｉ、Ｍｇ、Ａｌ及びＭｎからなる群より選ばれた少なくとも１種の元素が選ばれ、単一金属や合金、金属酸化物の形態で使用される。
【００１８】
粒子状のリチウム含有遷移金属酸化物１１の材質には、ＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４からなる群より選ばれた少なくとも１種か、又はＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４の組成の一部を金属元素で置換した非化学量論的化合物からなる群より選ばれた少なくとも１種のどちらか一方又は双方が含まれる。
導電性添加材料１４に粒子状の炭素系材料を更に含むことにより、粒子状の炭素系材料によってカーボンナノファイバ同士の接触が良好になり、高率充放電特性が更に向上する。また活物質の有効利用率が向上し、容量の増加に繋がる。この炭素系材料としては、石炭、コークス、ポリアクリロニトリル系炭素繊維、ピッチ系炭素繊維、有機物の炭素化品、天然黒鉛、人造黒鉛、合成黒鉛、メソカーボンマイクロビーズ、有機物の黒鉛化品及び黒鉛繊維からなる群より選ばれた少なくとも１種が含まれる。
【００１９】
次に、本発明の正極活物質の製造方法を説明する。
先ず、本発明の導電性添加材料を製造するために必要な触媒を合成する。この触媒の平均粒径は１０ｎｍ〜５００ｎｍの範囲内の微粉末が導電性添加材料を製造する際に好適な大きさである。触媒としてはＦｅ系微粉末、具体的には、Ｆｅ−Ｎｉ合金、Ｆｅ−Ｃｏ合金、Ｆｅ−Ｍｎ合金、Ｃｕ−Ｎｉ合金、Ｃｏ金属、Ｆｅ金属、Ａｌ２Ｏ３やＭｇＯ金属酸化物等が挙げられる。触媒は導電性添加材料を製造する前に前処理を施し、活性化させる。触媒をＨｅ及びＨ２を含む混合ガス雰囲気下で加熱することにより活性化される。
【００２０】
図６に本発明の導電性添加材料１４を製造する熱処理炉２０を示す。この熱処理炉２０は断熱性材質からなる装置本体２１から構成され、装置本体２１内部は所定の間隔をあけて２枚の仕切板２６により水平に仕切られる。仕切板２６，２６により仕切られた装置本体２１内部の頂部及び底部には発熱体２２がそれぞれ設置される。熱処理炉内で熱処理に用いられる発熱体２２の加熱源としては白熱ランプ、ハロゲンランプ、アークランプ、グラファイトヒータ等が挙げられる。
仕切板２６，２６で仕切られた空間に原料ガスを供給するように装置本体２１の一方の側部には、ガス供給口２４が設けられる。原料ガスとしては、ＣＯ及びＨ２を含む混合ガスが挙げられる。ＣＯの代わりにＣ２Ｈ２、Ｃ６Ｈ６等を用いてもよい。仕切板２６，２６により仕切られた空間２７は、微粉末の触媒をばらまいたテーブル２８が収容可能な大きさを有し、装置本体２１の他方の側部には系外へ熱処理炉２０内に供給した原料ガスを排出するガス排出口２９が設けられる。空間２７内に収容されるテーブル２８は取出し台３１の上に載置されて、熱処理炉内に収容、搬出可能に設けられる。
【００２１】
テーブル２８に微粉末の触媒３２を載せた後、そのテーブル２８を取出し台３１の上に載せて熱処理炉２０まで搬送し、装置本体２１の空間２７内に収納する。その後、原料ガスをガス供給口２４から供給し、発熱体２２，２２により加熱する。原料ガスの供給量は０．２Ｌ／ｍｉｎ〜１０Ｌ／ｍｉｎ、加熱温度は５００℃〜７００℃に設定される。原料ガスを供給しながら加熱し、１時間〜１０時間保持しておくことにより、触媒３２を介してカーボンナノファイバ及び粒子状凝集体をそれぞれ含む混合物３３が成長する。得られたカーボンナノファイバ及び粒子状凝集体を含む混合物３３には触媒が含まれているので、熱処理炉２０内よりテーブル２８を搬出して得られた混合物３３を取出し、この混合物３３を硝酸、硫酸、フッ酸等の酸性溶液に浸漬させて、混合物３３に含まれる触媒３２を除去する。なお、触媒３２をそのまま混合物中に含ませ、この触媒を金属又は金属酸化物としてもよい。
【００２２】
次に、粒子状のリチウム含有遷移金属酸化物と上記導電性添加材料とを導電性添加材料１４が活物質全体重量に対して０．５重量％〜１５重量％の割合となるように混合することにより本発明の正極活物質が得られる。ここで粒子状のリチウム含有遷移金属酸化物１１としては、ＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４からなる群より選ばれた少なくとも１種か、又はＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４の組成の一部を金属元素で置換した非化学量論的化合物からなる群より選ばれた少なくとも１種のどちらか一方又は双方を含む平均粒径３μｍ〜４０μｍの材料を用意する。
【００２３】
このようにして得られた本発明の正極活物質を用いて正極を作製する。
先ず得られたリチウム含有遷移金属酸化物及び導電性添加材料を含む正極活物質と、バインダとを所定の割合で混合することにより正極スラリーを調製する。バインダとしては、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶｄＦ）、エチレン−プロピレン−ジエン共重合体（ＥＰＤＭ）、スチレン−ブタジエンゴム（ＳＢＲ）等が挙げられる。次に正極スラリーを正極集電体箔の上面に、スクリーン印刷法やドクターブレード法等により塗布して乾燥して正極を作製する。正極集電板としては、アルミニウム箔、ステンレス鋼箔、ニッケル箔等が挙げられる。なお、正極スラリーをガラス基板上に塗布し乾燥した後に、ガラス基板から剥離して正極フィルムを作製し、更にこの正極フィルムを正極集電体に重ねて所定の圧力でプレス成形することにより、正極を作製してもよい。このように製造された正極では、グラファイト網が複数積層されて形成されたカーボンナノファイバが粒子状のリチウム含有遷移金属酸化物１１が形成する空隙に充填されることで、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。
【００２４】
得られた本発明の正極と、非水電解液［例えば、エチレンカーボネート（ＥＣ）とジエチレンカーボネート（ＤＥＣ）からなる混合溶媒（混合重量比１：１）と過塩素酸リチウムを１モル／リットル溶解させたもの］を含む電解質層と、負極集電体上に負極活物質、結着剤及びバインダからなる負極スラリーをドクターブレード法によって塗布し乾燥することにより形成された負極とを積層することにより、リチウムイオン電池が得られる。
また本発明の正極と、ポリエチレンオキシドやポリフッ化ビニリデン等からなるポリマー電解質層と、負極集電体上に負極活物質、結着剤及びバインダからなる負極スラリーをドクターブレード法によって塗布し乾燥することにより形成された負極とを積層することにより、リチウムポリマー電池が得られる。
【００２５】
このように製造されたリチウムイオン電池やリチウムポリマー電池では、グラファイト網が複数積層されて形成されたカーボンナノファイバが粒子状のリチウム含有遷移金属酸化物が形成する空隙に充填されることで、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。また、従来より用いられてきた炭素材料に比べて、サイズの小さいカーボンナノファイバを用いているため、高密度での充電が可能となり、電池のエネルギ密度向上につながる。
【００２６】
【実施例】
次に本発明の実施例を比較例とともに詳しく説明する。
＜実施例１＞
（１） 導電性添加材料の製造
先ず、平均粒径０．２μｍのＦｅ−Ｎｉ合金を触媒とし、この触媒をＨｅ及びＨ２を含む混合ガス雰囲気下で加熱して活性化させた。次いで活性化させた触媒をテーブル上に載せ、テーブルを熱処理炉内に収容した。次に、熱処理炉内を５５０℃〜６３０℃の温度に加熱し、ＣＯとＨ２を含む混合ガスを原料ガスとしてこの原料ガスを流量１０Ｌ／分で熱処理炉内に供給しながら約１０時間保持してカーボンナノファイバ及び粒子状凝集体をそれぞれ含む混合物（以下、カーボンナノファイバと略す。）を合成した。得られたカーボンナノファイバを導電性添加材料とした。このカーボンナノファイバをＸ線回折により測定したところ、カーボンナノファイバのグラファイト網平面の積層間隔ｄ００２は０．３３６２ｎｍであった。
【００２７】
（２） 正極（作用極）の作製
先ず、リチウム含有遷移金属酸化物として平均粒径１５μｍのＬｉＣｏＯ２（容量１４０ｍＡｈ／ｇ）、バインダとしてポリフッ化ビニリデン（ＰＶｄＦ）をそれぞれ用意した。次いで、ＬｉＣｏＯ２とＰＶｄＦと上記得られたカーボンナノファイバとを９０重量％：９重量％：１重量％の割合で混合し、この混合物をｎ−メチルピロリドンに溶解分散させて正極スラリーを調製した。次に、上記正極スラリーを正極集電体上に塗布して乾燥した後に圧延することにより厚さ０．０９ｃｍの正極フィルムを作製した。正極集電体にはアルミ箔を用いた。この正極フィルムを縦×横がそれぞれ１ｃｍ×１ｃｍの正方形に切断して、正方形の正極（作用極）を得た。
【００２８】
＜実施例２＞
ＬｉＣｏＯ２とＰＶｄＦとカーボンナノファイバの割合を８９重量％：９重量％：２重量％とした以外は実施例１と同様にして正極（作用極）を作製した。
＜実施例３＞
ＬｉＣｏＯ２とＰＶｄＦとカーボンナノファイバの割合を８８重量％：９重量％：３重量％とした以外は実施例１と同様にして正極（作用極）を作製した。
＜実施例４＞
ＬｉＣｏＯ２とＰＶｄＦとカーボンナノファイバの割合を８６重量％：９重量％：５重量％とした以外は実施例１と同様にして正極（作用極）を作製した。
＜実施例５＞
ＬｉＣｏＯ２とＰＶｄＦとカーボンナノファイバの割合を８１重量％：９重量％：１０重量％とした以外は実施例１と同様にして正極（作用極）を作製した。
【００２９】
＜実施例６＞
導電性添加材料として粒子状の炭素系材料（電気化学工業社製、デンカブラック）を更に加え、ＬｉＣｏＯ２とＰＶｄＦとカーボンナノファイバと炭素系材料の割合を８５重量％：９重量％：３重量％：３重量％とした以外は実施例１と同様にして正極（作用極）を作製した。
＜実施例７＞
ＬｉＣｏＯ２とＰＶｄＦとカーボンナノファイバと炭素系材料の割合を８６重量％：９重量％：２重量％：３重量％とした以外は実施例６と同様にして正極（作用極）を作製した。
【００３０】
＜比較例１＞
導電性添加材料としてカーボンナノファイバを加えず、ＬｉＣｏＯ２とＰＶｄＦと炭素系材料の割合を８１重量％：９重量％：１０重量％とした以外は実施例６と同様にして正極（作用極）を作製した。
＜比較例２＞
ＬｉＣｏＯ２とＰＶｄＦと炭素系材料の割合を８１重量％：９重量％：５重量％とした以外は比較例１と同様にして正極（作用極）を作製した。
＜比較例３＞
ＬｉＣｏＯ２とＰＶｄＦと炭素系材料の割合を８１重量％：９重量％：１０重量％とした以外は比較例１と同様にして正極（作用極）を作製した。
【００３１】
＜比較試験及び評価＞
図７に示すように、実施例１〜７及び比較例１〜３でそれぞれ作製した正極４１（作用極）を充放電サイクル試験装置５１に取付けた。この装置５１は、容器５２に電解液５３（リチウム塩を有機溶媒に溶かしたもの）が貯留され、上記正極４１が負極４２及び参照極４３とともに電解液５３に浸され、更に正極４１（作用極）、負極４２（対極）及び参照極４３がポテンシオスタット５４（ポテンショメータ）にそれぞれ電気的に接続された構成となっている。リチウム塩には１ＭのＬｉＰＦ６を、有機溶媒にはエチレンカーボネート及びジエチルカーボネートをそれぞれ含む溶液を用いた。この装置を用いて充放電サイクル試験を行い、各正極（作用極）の低率及び高率放電容量を測定した。なお、低率放電容量は２５ｍＡ／ｇにて、高率放電容量は１５０ｍＡ／ｇにてそれぞれ測定を行い、測定電圧範囲を４．３Ｖ〜３Ｖとした。実施例１〜７及び比較例１〜３の電極の測定結果を表１にそれぞれ示す。
【００３２】
【表１】

Figure 2004220909
【００３３】
表１より明らかなように、正極活物質にカーボンナノファイバを含まない比較例１〜３では、高率放電容量の低下が著しい結果となった。また、電極の重量に対する容量が明らかに低下した結果となった。これに対して本発明の正極活物質を用いた実施例１〜７では、低率放電容量と高率放電容量に大きな差はなく、この材料を用いて電極を作製した場合、高率放電特性が向上できることが判った。
また、電極重量に対する容量が著しく向上することが判った。
【００３４】
【発明の効果】
以上述べたように、本発明の正極活物質は、平均粒径３μｍ〜４０μｍの粒子状のリチウム含有遷移金属酸化物と平均直径１０ｎｍ〜５００ｎｍの平面状のグラファイト網が複数積層され、グラファイト網がファイバの縦軸に対して実質的に垂直であるカーボンナノファイバを主成分とする導電性添加材料をそれぞれ含み、この導電性添加材料に含まれるカーボンナノファイバが１０００ｎｍ以上の長さと、１０以上のアスペクト比を有し、導電性添加材料が活物質全体重量に対して０．５重量％〜１５重量％である。
導電性添加材料の主成分であるナノサイズのカーボンナノファイバを含む本発明の正極活物質を用いて電池の電極を作製した場合、粒子状のリチウム含有遷移金属酸化物が形成する空隙に導電性添加材料が充填されることで、エネルギ密度の低下を抑制し、出力特性の向上が可能になる。また、本発明の導電性添加材料の主成分である１０００ｎｍ以上の長さと、１０以上のアスペクト比を有するカーボンナノファイバはグラファイト網が複数積層された構造を持つため、軸方向に垂直な導電方向を有する。従って、従来の炭素材料やカーボンナノチューブを添加する場合に比べて少量の添加で導電性が大幅に高まる。
また本発明の正極活物質は、導電性添加材料がカーボンナノファイバに加えて、更に黒鉛構造を有する炭素微粉からなる粒子状凝集体を含み、カーボンナノファイバが８０重量％〜９９．５、粒子状凝集体が０．５重量％〜２０重量％の割合である。導電性添加材料に粒子状凝集体を含むことによって主成分であるカーボンナノファイバ同士の接触が良好になり、高率充放電特性が更に向上する。
【図面の簡単な説明】
【図１】本発明の正極活物質の模式図。
【図２】本発明の導電性添加材料の主成分であるカーボンナノファイバの模式図。
【図３】本発明のカーボンナノファイバの導電方向を示す図。
【図４】カーボンナノファイバと粒子状凝集体を示す模式図。
【図５】図２に対応する別の構造を有するカーボンナノファイバの模式図。
【図６】本発明の導電性添加材料を作製する熱処理炉の断面構成図。
【図７】実施例及び比較例のリチウム二次電池用正極活物質の充放電サイクル試験に用いられる装置。
【図８】カーボンナノチューブの導電方向を示す図。
【符号の説明】
１１ リチウム含有遷移金属酸化物
１２ グラファイト網
１３ カーボンナノファイバ
１４ 導電性添加材料
１６ 粒子状凝集体[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a positive electrode active material, a positive electrode using the same, and a lithium ion battery and a lithium polymer battery using the positive electrode, which can suppress a decrease in energy density of a battery and improve output characteristics.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the development of portable electronic devices such as mobile phones and notebook computers and the practical use of electric vehicles, secondary batteries of small size, light weight and high capacity have been required. At present, as a high-capacity secondary battery that meets this demand, LiCoO 2 Lithium ion secondary batteries using lithium-containing transition metal oxides and the like and a carbon-based material as a negative electrode active material have been commercialized. The lithium ion secondary battery has attracted attention as a power source for portable electronic devices because it has a high energy density and can be reduced in size and weight.
Since the electron conductivity of the positive electrode active material is not so high and belongs to semiconductors in many cases, in order to secure the conductivity of the electrode, a positive electrode mixture is prepared by adding a conductive agent and using a binder. Conventionally, carbon, acetylene black, graphite, and the like have been used as the conductive agent. To increase the high-rate discharge characteristics of the battery, the characteristics can be obtained by increasing the ratio of the conductive agent in the positive electrode.However, the presence of a large amount of the conductive agent decreases the content ratio of the lithium-containing transition metal oxide. This causes a problem that the discharge capacity is reduced.
[0003]
As a technique for solving the above problems, a positive electrode in which a mixture layer having a positive electrode active material, a conductive agent, and a binder is formed on a metal substrate, a negative electrode, and an organic electrolyte, the positive electrode active material containing manganese In an organic electrolyte battery mainly composed of a lithium composite oxide, an organic electrolyte battery in which the conductive agent is a carbon nanotube is disclosed (for example, see Patent Document 1). The organic electrolyte battery using the carbon nanotubes as a conductive agent can improve the conductivity between the positive electrode active materials, and can realize an organic electrolyte battery excellent in high rate discharge characteristics and charge / discharge cycle characteristics.
In addition, a non-aqueous secondary using an amorphous carbon material having an average particle size of 100 nm or less and a graphite-based carbon material having an average particle size of 1 to 10 μm as a conductive auxiliary using a lithium-containing composite oxide as a positive electrode active material. A positive electrode for a battery is also disclosed (for example, see Patent Document 2). The amorphous carbon material having an average particle size of 100 μm used in the conductive additive is formed by spinning carbon black such as acetylene black and Ketjen black, vapor-grown carbon fiber, carbon nanotube, and pitch to carbonize. Carbonized fiber or the like is used. By using particles of an amorphous carbon material having an average particle diameter of 100 μm, it is easy to enter the gaps between the active material particles and the filling property can be enhanced. Therefore, a material having a high operating voltage of 4.5 V or more is used as the positive electrode active material. Even if it does, the cycle characteristics and the additional characteristics are excellent.
[0004]
[Patent Document 1]
JP-A-11-283629
[Patent Document 2]
JP 2002-279998 A
[0005]
[Problems to be solved by the invention]
However, in the batteries disclosed in Patent Literature 1 and Patent Literature 2, a carbon material or a carbon nanotube having a small particle size is used as a conductive agent in order to obtain conductivity of the positive electrode. In addition, since the carbon nanotube has a graphite network oriented parallel to the fiber axis, it is easy to conduct electricity in parallel to the axial direction. Therefore, there is a problem that only conductivity that is not much different from carbon, acetylene black, graphite, etc., which has been conventionally used as a conductive agent, is obtained, and the conductivity between lithium-containing transition metal oxides cannot be sufficiently increased. Was.
An object of the present invention is to provide a positive electrode active material, a positive electrode using the same, and a lithium ion battery and a lithium polymer battery using the positive electrode, which can suppress a decrease in energy density of the battery and improve output characteristics. Is to do.
[0006]
[Means for Solving the Problems]
The invention according to claim 1 is, as shown in FIG. 1, a plurality of laminated lithium-containing transition metal oxides 11 having an average particle diameter of 3 μm to 40 μm and a plurality of planar graphite nets 12 having an average diameter of 10 nm to 500 nm, The graphite network includes a conductive additive material 14 mainly composed of carbon nanofibers 13 that are substantially perpendicular to the longitudinal axis of the fiber, and the carbon nanofibers 13 included in the conductive additive material 14 are 1000 nm or more. And an aspect ratio of 10 or more, and the conductive additive material 14 is 0.5% by weight to 15% by weight based on the total weight of the active material.
In the invention according to claim 1, when a battery electrode is manufactured using the positive electrode active material of the present invention, planar graphite having an average diameter of 10 nm to 500 nm is formed in a void formed by the particulate lithium-containing transition metal oxide 11. Filling with the conductive additive material 14 mainly composed of the carbon nanofibers 13 formed by laminating a plurality of nets 12 increases conductivity, suppresses a decrease in energy density, and improves output characteristics. Become.
As shown in FIG. 3, a carbon nanofiber 13 having a length of 1000 nm or more and an aspect ratio of 10 or more, which is a main component of the conductive additive material 14 of the present invention, has a structure in which a plurality of graphite nets 12 are stacked. It is oriented perpendicular to the fiber axis and easily conducts perpendicular to the axial direction. Therefore, compared to the case where a conventional carbon material or carbon nanotube is added, the conductivity is greatly increased by adding a small amount.
[0007]
The invention according to claim 2 is the invention according to claim 1, wherein, as shown in FIG. 4, in addition to the carbon nanofibers 13, the conductive additive material 14 further comprises a carbon fine powder having a graphite structure. The positive electrode active material includes the aggregates 16, wherein the carbon nanofibers 13 are in a ratio of 80 wt% to 99.5 wt%, and the particulate aggregates 16 are in a ratio of 0.5 wt% to 20 wt%.
According to the second aspect of the present invention, by including the particulate aggregates 16 in the conductive additive material 14, the contact between the carbon nanofibers 13, which are the main components, is improved, and the high-rate charge / discharge characteristics are further improved.
[0008]
The invention according to claim 3 is the invention according to claim 1 or 2, wherein in the X-ray diffraction of carbon nanofibers contained in the conductive additive material 14, or a mixture containing each of the carbon nanofibers and the particulate aggregate. Lamination interval d of the graphite net 12 plane to be measured 002 Is a positive electrode active material having a thickness of 0.3354 nm to 0.339 nm.
The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the conductive additive material 14 has one or both of a metal and a metal oxide 17 having an average particle size of 10 nm to 500 nm. Is a positive electrode active material further containing 0.5% by weight to 10% by weight.
In the invention according to claim 4, since the conductive additive material 14 further includes a metal or a metal oxide 17 having an average particle size of 10 nm to 500 nm, the metal or the metal oxide becomes a base point of electron conduction. Rate discharge is possible.
[0009]
The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the exposed portion of the carbon nanofiber 13 or the exposed portion of the mixture containing the carbon nanofiber 13 and the particulate aggregate 16 respectively. At least 85% of the positive electrode active material is the end of the graphite network.
The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein one or both of the metal and the metal oxide is a positive electrode active material on the long axis of the carbon nanofiber. is there.
The invention according to claim 7 is the invention according to claim 4 or 6, wherein the metal is at least one element selected from the group consisting of Fe, Co, Ni, Mg, Al and Mn. It is.
[0010]
The invention according to claim 8 is the invention according to claim 1, wherein the particulate lithium-containing transition metal oxide 11 is LiCoO 2. 2 , LiNiO 2 And LiMn 2 O 4 At least one selected from the group consisting of 2 , LiNiO 2 And LiMn 2 O 4 Is a positive electrode active material containing at least one or both selected from the group consisting of non-stoichiometric compounds in which a part of the composition is replaced with a metal element.
The invention according to claim 9 is the invention according to any one of claims 1 to 8, wherein the conductive additive material further includes a particulate carbon-based material, and the carbon-based material is coal, coke, or polyacrylonitrile. Positive electrode containing at least one selected from the group consisting of carbonaceous carbon fibers, pitch-based carbon fibers, carbonized organic materials, natural graphite, artificial graphite, synthetic graphite, mesocarbon microbeads, graphitized organic materials, and graphite fibers Active material.
According to the ninth aspect of the invention, the contact between the carbon nanofibers is improved by the particulate carbon-based material, and the high-rate charge / discharge characteristics are further improved. Further, the effective utilization rate of the active material is improved, which leads to an increase in capacity.
[0011]
The invention according to claim 10 is a positive electrode formed using the positive electrode active material according to any one of claims 1 to 9 and a binder.
In the positive electrode according to the tenth aspect, the carbon nanofibers formed by laminating a plurality of graphite networks are filled in the voids formed by the particulate lithium-containing transition metal oxide, whereby the conductivity is increased, and the energy is increased. It is possible to suppress a decrease in density and improve output characteristics.
[0012]
The invention according to claim 11 is a lithium ion battery formed using the positive electrode according to claim 10.
The invention according to claim 12 is a lithium polymer battery formed using the positive electrode according to claim 10.
In the lithium ion battery or the lithium polymer battery according to the eleventh or twelfth aspect, the carbon nanofiber formed by laminating a plurality of graphite networks is filled in the voids formed by the particulate lithium-containing transition metal oxide. As a result, conductivity is increased, a decrease in energy density is suppressed, and output characteristics can be improved. In addition, since carbon nanofibers having a smaller size than conventionally used carbon materials are used, high-density charging is possible, which leads to an improvement in the energy density of the battery.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, a positive electrode of a lithium ion battery or a lithium polymer battery is composed of a particulate lithium-containing transition metal oxide 11 having an average particle diameter of 3 μm to 40 μm and a planar graphite network having an average diameter of 10 nm to 500 nm. A positive electrode active material is used which includes a plurality of layers 12 and a conductive additive material 14 mainly composed of carbon nanofibers 13 whose graphite network is substantially perpendicular to the longitudinal axis of the fiber. The carbon nanofibers 13 included in the conductive additive material 14 are configured to have a length of 1000 nm or more and an aspect ratio of 10 or more. It is preferable that the average diameter is 20 nm to 300 nm, the length is 1000 nm to 6000 nm, and the aspect ratio is 20 to 200. When a battery electrode is manufactured using the positive electrode active material of the present invention including the particulate lithium-containing transition metal oxide 11 having a large average particle diameter and the nano-sized conductive additive material 14, the lithium-containing transition metal oxide is used. Since the conductive additive material 14 is filled in the voids formed by 11, a decrease in energy density can be suppressed, and output characteristics can be improved. The carbon nanofibers 13 having a length of 1000 nm or more and an aspect ratio of 10 or more, which are the main components of the conductive additive material 14 of the present invention, have a structure in which a plurality of graphite nets 12 are stacked, and are oriented perpendicular to the fiber axis. It is easy to conduct electricity perpendicular to the axial direction. Therefore, compared to the case where a conventional carbon material or carbon nanotube is added, the conductivity is greatly increased by adding a small amount. As shown in FIG. 5, one side of one end 12a of the graphite net 12 is joined to one side of the end of another graphite net, and one side of another end is one side of the end of another graphite net. The carbon nanofiber 13 formed by bonding with each other and having a structure folded from each side may be used.
[0014]
In the positive electrode active material of the present invention, the conductive additive material 14 is formed in a ratio of 0.5% by weight to 15% by weight based on the total weight of the active material. The ratio of the conductive additive material 14 is preferably 1% by weight to 10% by weight based on the total weight of the active material. When a positive electrode is formed using a positive electrode active material in which the ratio of the conductive additive material 14 is less than 0.5% by weight based on the total weight of the active material, sufficient conductivity cannot be obtained, the capacity is low, and the output characteristics are poor. When a positive electrode is formed using a positive electrode active material in which the ratio of the conductive additive material 14 exceeds 15% by weight with respect to the total weight of the active material, a ratio of the active material in the electrode decreases, and the energy density of the electrode decreases. Occurs.
[0015]
Further, by setting the average diameter of the graphite net 12 in the range of 10 nm to 500 nm, an optimum conductivity improving effect can be obtained. If the average diameter of the graphite network 12 is less than 10 nm, there is a problem in that contact between adjacent lithium-containing transition metal oxides cannot be sufficiently obtained, and if it exceeds 500 nm, it is difficult to fit in the voids of the lithium-containing transition metal oxide. Is generated.
In addition, carbon nanofibers are smaller in size than conductive additives that have been used in the past. Therefore, when a battery electrode is manufactured, high-density charging is possible, and the energy density of the battery is improved. Leads to.
[0016]
Further, as shown in FIG. 4, the conductive additive material 14 of the present invention further includes, in addition to the carbon nanofibers 13, a particulate aggregate 16 made of carbon fine powder having a graphite structure. The content of the carbon nanofibers 13 in the conductive additive material is 80% by weight to 99.5% by weight, and the content of the particulate aggregate 16 is 0.5% by weight to 20% by weight. Preferably, the ratio of the carbon nanofibers 13 is 90% by weight to 99% by weight, and the ratio of the particulate aggregates 16 is 1% by weight to 10% by weight. The reason why the content of the carbon nanofibers 13 is limited to the range of 80% by weight to 99.5% by weight is that when less than 80% by weight, the effect of the conductive addition is not sufficient. This is because the electrical contact between the fibers is reduced, and the effect of the addition of conductivity cannot be sufficiently obtained.
[0017]
When a carbon nanofiber or a mixture containing each of the carbon nanofiber and the particulate aggregate is measured by X-ray diffraction, the stacking distance d of the obtained graphite network plane is measured. 002 Is in the range of 0.3354 nm to 0.339 nm. Preferred stacking distance d 002 Is 0.3354 nm to 0.337 nm.
As shown in FIG. 4, 0.5% to 10% by weight of one or both of a metal and a metal oxide 17 having an average particle diameter of 10 nm to 500 nm is further included. Since the metal or metal oxide 17 serves as a starting point of electron conduction, a higher discharge rate is possible. It is preferable that at least 85% of the exposed portions of the carbon nanofibers 13 or the exposed portions of the mixture containing the carbon nanofibers 13 and the particulate aggregates 16 are ends of the graphite network. Here, the end portion of the graphite net indicates a portion indicated by reference numeral 12a in FIGS. One or both of the metal and the metal oxide are configured to be located on the long axis of the carbon nanofiber. As the metal, at least one element selected from the group consisting of Fe, Co, Ni, Mg, Al and Mn is selected and used in the form of a single metal, an alloy or a metal oxide.
[0018]
The material of the particulate lithium-containing transition metal oxide 11 is LiCoO 2 , LiNiO 2 And LiMn 2 O 4 At least one selected from the group consisting of 2 , LiNiO 2 And LiMn 2 O 4 At least one selected from the group consisting of non-stoichiometric compounds in which a part of the composition is replaced by a metal element.
When the conductive additive material 14 further includes a particulate carbon-based material, the contact between the carbon nanofibers is improved by the particulate carbon-based material, and the high-rate charge / discharge characteristics are further improved. Further, the effective utilization rate of the active material is improved, which leads to an increase in capacity. Examples of the carbon-based material include coal, coke, polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, carbonized organic material, natural graphite, artificial graphite, synthetic graphite, mesocarbon microbeads, graphitized organic material, and graphite fiber. At least one selected from the group consisting of:
[0019]
Next, a method for producing the positive electrode active material of the present invention will be described.
First, a catalyst necessary for producing the conductive additive material of the present invention is synthesized. The average particle size of the catalyst is in the range of 10 nm to 500 nm, and the fine powder is suitable for producing the conductive additive material. As the catalyst, Fe-based fine powder, specifically, Fe-Ni alloy, Fe-Co alloy, Fe-Mn alloy, Cu-Ni alloy, Co metal, Fe metal, Al 2 O 3 And MgO metal oxide. The catalyst is pre-treated and activated before producing the conductive additive material. The catalyst is He and H 2 Activated by heating in a mixed gas atmosphere containing
[0020]
FIG. 6 shows a heat treatment furnace 20 for producing the conductive additive material 14 of the present invention. The heat treatment furnace 20 includes an apparatus main body 21 made of a heat insulating material, and the inside of the apparatus main body 21 is horizontally partitioned by two partition plates 26 at a predetermined interval. Heating elements 22 are installed at the top and bottom inside the apparatus main body 21 separated by the partition plates 26, 26, respectively. Examples of the heat source of the heating element 22 used for the heat treatment in the heat treatment furnace include an incandescent lamp, a halogen lamp, an arc lamp, and a graphite heater.
A gas supply port 24 is provided on one side of the apparatus main body 21 so as to supply the raw material gas to the space partitioned by the partition plates 26, 26. CO and H are used as source gases. 2 And a mixed gas containing: C instead of CO 2 H 2 , C 6 H 6 Etc. may be used. The space 27 divided by the partition plates 26, 26 has a size capable of accommodating the table 28 in which the fine powder catalyst is dispersed, and the other side of the apparatus main body 21 is out of the system and into the heat treatment furnace 20. A gas outlet 29 for discharging the supplied source gas is provided. The table 28 accommodated in the space 27 is placed on the take-out table 31 and is provided so as to be accommodated in and out of the heat treatment furnace.
[0021]
After placing the fine powder catalyst 32 on the table 28, the table 28 is placed on the take-out table 31, transported to the heat treatment furnace 20, and stored in the space 27 of the apparatus main body 21. After that, the raw material gas is supplied from the gas supply port 24 and heated by the heating elements 22 and 22. The supply rate of the raw material gas is set to 0.2 L / min to 10 L / min, and the heating temperature is set to 500 ° C. to 700 ° C. By heating while supplying the raw material gas and holding for 1 hour to 10 hours, the mixture 33 containing the carbon nanofiber and the particulate aggregate is grown via the catalyst 32. Since the obtained mixture 33 containing carbon nanofibers and particulate aggregates contains a catalyst, the mixture 33 obtained by unloading the table 28 from the heat treatment furnace 20 is taken out. The catalyst 32 contained in the mixture 33 is removed by immersion in an acidic solution such as sulfuric acid or hydrofluoric acid. The catalyst 32 may be directly contained in the mixture, and the catalyst may be a metal or a metal oxide.
[0022]
Next, the particulate lithium-containing transition metal oxide and the above-mentioned conductive additive material are mixed so that the conductive additive material 14 accounts for 0.5% by weight to 15% by weight based on the total weight of the active material. Thereby, the positive electrode active material of the present invention is obtained. Here, as the particulate lithium-containing transition metal oxide 11, LiCoO 2 , LiNiO 2 And LiMn 2 O 4 At least one selected from the group consisting of 2 , LiNiO 2 And LiMn 2 O 4 A material having an average particle size of 3 μm to 40 μm, including at least one or both selected from the group consisting of non-stoichiometric compounds in which a part of the composition is replaced by a metal element, is prepared.
[0023]
A positive electrode is manufactured using the thus obtained positive electrode active material of the present invention.
First, a positive electrode slurry is prepared by mixing the obtained positive electrode active material containing the lithium-containing transition metal oxide and the conductive additive material with a binder at a predetermined ratio. Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EPDM), and styrene-butadiene rubber (SBR). Next, the positive electrode slurry is applied to the upper surface of the positive electrode current collector foil by a screen printing method, a doctor blade method, or the like, and dried to produce a positive electrode. Examples of the positive electrode current collector plate include an aluminum foil, a stainless steel foil, and a nickel foil. The positive electrode slurry was applied on a glass substrate, dried, and then peeled off from the glass substrate to produce a positive electrode film. The positive electrode film was further laminated on the positive electrode current collector and pressed at a predetermined pressure to form the positive electrode film. May be produced. In the positive electrode manufactured as described above, the carbon nanofibers formed by laminating a plurality of graphite networks are filled in the voids formed by the particulate lithium-containing transition metal oxide 11, thereby suppressing a decrease in energy density. Thus, the output characteristics can be improved.
[0024]
The obtained positive electrode of the present invention, a nonaqueous electrolytic solution [for example, a mixed solvent of ethylene carbonate (EC) and diethylene carbonate (DEC) (mixing weight ratio 1: 1) and lithium perchlorate dissolved at 1 mol / liter] And a negative electrode formed by applying and drying a negative electrode slurry composed of a negative electrode active material, a binder and a binder on a negative electrode current collector by a doctor blade method, and drying the resultant. Thus, a lithium ion battery is obtained.
The positive electrode of the present invention, a polymer electrolyte layer made of polyethylene oxide or polyvinylidene fluoride, and the like, and a negative electrode active material, a negative electrode slurry composed of a binder and a binder applied on a negative electrode current collector by a doctor blade method and dried. By stacking the negative electrode formed by the method described above, a lithium polymer battery is obtained.
[0025]
In the lithium ion battery and the lithium polymer battery manufactured in this manner, carbon nanofibers formed by laminating a plurality of graphite networks are filled in the voids formed by the particulate lithium-containing transition metal oxide, so that the energy is reduced. It is possible to suppress a decrease in density and improve output characteristics. In addition, since carbon nanofibers having a smaller size than conventionally used carbon materials are used, high-density charging is possible, which leads to an improvement in the energy density of the battery.
[0026]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
(1) Production of conductive additive materials
First, a Fe—Ni alloy having an average particle size of 0.2 μm was used as a catalyst, and this catalyst was used as He and H 2 And activated in a mixed gas atmosphere containing. Next, the activated catalyst was placed on a table, and the table was housed in a heat treatment furnace. Next, the inside of the heat treatment furnace is heated to a temperature of 550 ° C. to 630 ° C., and CO and H 2 A mixture containing carbon nanofibers and particulate agglomerates (hereinafter abbreviated as carbon nanofibers) is maintained for about 10 hours while supplying the source gas into the heat treatment furnace at a flow rate of 10 L / min using a mixed gas containing .) Was synthesized. The obtained carbon nanofiber was used as a conductive additive material. When this carbon nanofiber was measured by X-ray diffraction, the stacking distance d of the carbon nanofiber graphite plane was measured. 002 Was 0.3362 nm.
[0027]
(2) Preparation of positive electrode (working electrode)
First, as a lithium-containing transition metal oxide, LiCoO having an average particle size of 15 μm was used. 2 (Capacity: 140 mAh / g), and polyvinylidene fluoride (PVdF) was prepared as a binder. Then, LiCoO 2 , PVdF, and the obtained carbon nanofiber were mixed at a ratio of 90% by weight: 9% by weight: 1% by weight, and this mixture was dissolved and dispersed in n-methylpyrrolidone to prepare a positive electrode slurry. Next, the positive electrode slurry was coated on a positive electrode current collector, dried, and then rolled to produce a positive electrode film having a thickness of 0.09 cm. Aluminum foil was used for the positive electrode current collector. This positive electrode film was cut into squares each measuring 1 cm × 1 cm in length and width to obtain a square positive electrode (working electrode).
[0028]
<Example 2>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 1 except that the ratio of PVdF and carbon nanofiber was 89% by weight: 9% by weight: 2% by weight.
<Example 3>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 1, except that the ratio of PVdF to carbon nanofiber was set to 88% by weight: 9% by weight: 3% by weight.
<Example 4>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 1 except that the ratio of PVdF and carbon nanofiber was changed to 86% by weight: 9% by weight: 5% by weight.
<Example 5>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 1, except that the ratio of PVdF and carbon nanofiber was set to 81% by weight: 9% by weight: 10% by weight.
[0029]
<Example 6>
A particulate carbon-based material (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) is further added as a conductive additive material, and LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 1 except that the ratio of PVdF, carbon nanofiber, and carbon-based material was changed to 85% by weight: 9% by weight: 3% by weight: 3% by weight.
<Example 7>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 6 except that the ratio of PVdF, carbon nanofiber, and carbon-based material was changed to 86% by weight: 9% by weight: 2% by weight: 3% by weight.
[0030]
<Comparative Example 1>
Without adding carbon nanofiber as conductive additive material, LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Example 6, except that the ratio of PVdF to the carbon-based material was changed to 81% by weight: 9% by weight: 10% by weight.
<Comparative Example 2>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Comparative Example 1, except that the ratio of PVdF and the carbon-based material was changed to 81% by weight: 9% by weight: 5% by weight.
<Comparative Example 3>
LiCoO 2 A positive electrode (working electrode) was produced in the same manner as in Comparative Example 1, except that the ratio of PVdF to the carbon-based material was changed to 81% by weight: 9% by weight: 10% by weight.
[0031]
<Comparison test and evaluation>
As shown in FIG. 7, the positive electrodes 41 (working electrodes) produced in Examples 1 to 7 and Comparative Examples 1 to 3 were attached to a charge / discharge cycle test device 51. In this device 51, an electrolyte 53 (a solution in which a lithium salt is dissolved in an organic solvent) is stored in a container 52, and the positive electrode 41 is immersed in the electrolyte 53 together with the negative electrode 42 and the reference electrode 43. ), The negative electrode 42 (counter electrode) and the reference electrode 43 are electrically connected to a potentiostat 54 (potentiometer), respectively. 1M LiPF for lithium salt 6 And a solution containing ethylene carbonate and diethyl carbonate as the organic solvent, respectively. A charge / discharge cycle test was performed using this device, and the low-rate and high-rate discharge capacities of each positive electrode (working electrode) were measured. The low-rate discharge capacity was measured at 25 mA / g, and the high-rate discharge capacity was measured at 150 mA / g. The measured voltage range was 4.3 V to 3 V. Table 1 shows the measurement results of the electrodes of Examples 1 to 7 and Comparative Examples 1 to 3, respectively.
[0032]
[Table 1]
Figure 2004220909
[0033]
As is clear from Table 1, in Comparative Examples 1 to 3 in which the carbon nanofiber was not contained in the positive electrode active material, the high rate discharge capacity was significantly reduced. In addition, the result showed that the capacity with respect to the weight of the electrode was clearly reduced. On the other hand, in Examples 1 to 7 using the positive electrode active material of the present invention, there was no significant difference between the low rate discharge capacity and the high rate discharge capacity. Was found to be able to be improved.
It was also found that the capacity with respect to the electrode weight was significantly improved.
[0034]
【The invention's effect】
As described above, the positive electrode active material of the present invention is formed by stacking a plurality of particulate lithium-containing transition metal oxides having an average particle size of 3 μm to 40 μm and a plurality of planar graphite networks having an average diameter of 10 nm to 500 nm. Each of the conductive additive materials contains a conductive additive material mainly composed of carbon nanofibers that is substantially perpendicular to the longitudinal axis of the fiber, and the carbon nanofibers contained in the conductive additive material have a length of 1000 nm or more and a length of 10 or more. It has an aspect ratio, and the conductive additive material is 0.5% by weight to 15% by weight based on the total weight of the active material.
When a battery electrode is manufactured using the positive electrode active material of the present invention including nano-sized carbon nanofibers, which is a main component of the conductive additive material, conductive particles are formed in voids formed by the particulate lithium-containing transition metal oxide. By filling the additive material, a decrease in energy density can be suppressed, and output characteristics can be improved. In addition, the carbon nanofiber having a length of 1000 nm or more and an aspect ratio of 10 or more, which is a main component of the conductive additive material of the present invention, has a structure in which a plurality of graphite nets are stacked, so that the conductive direction is perpendicular to the axial direction. Having. Therefore, compared to the case where a conventional carbon material or carbon nanotube is added, the conductivity is greatly increased by adding a small amount.
Further, the cathode active material of the present invention is characterized in that the conductive additive material further includes, in addition to the carbon nanofibers, a particulate aggregate of carbon fine powder having a graphite structure, wherein the carbon nanofibers are 80% by weight to 99.5%. The ratio of the agglomerates is from 0.5% by weight to 20% by weight. By including the particulate aggregate in the conductive additive material, the contact between the carbon nanofibers as the main components is improved, and the high-rate charge / discharge characteristics are further improved.
[Brief description of the drawings]
FIG. 1 is a schematic view of a positive electrode active material of the present invention.
FIG. 2 is a schematic view of a carbon nanofiber that is a main component of the conductive additive material of the present invention.
FIG. 3 is a view showing a conductive direction of the carbon nanofiber of the present invention.
FIG. 4 is a schematic diagram showing carbon nanofibers and particulate aggregates.
FIG. 5 is a schematic view of a carbon nanofiber having another structure corresponding to FIG. 2;
FIG. 6 is a sectional configuration view of a heat treatment furnace for producing a conductive additive material of the present invention.
FIG. 7 shows an apparatus used for a charge / discharge cycle test of the positive electrode active materials for lithium secondary batteries of Examples and Comparative Examples.
FIG. 8 is a diagram showing a conductive direction of a carbon nanotube.
[Explanation of symbols]
11 Lithium-containing transition metal oxides
12 Graphite net
13 Carbon nanofiber
14 Conductive additive materials
16 Particulate aggregates

Claims (12)

平均粒径３μｍ〜４０μｍの粒子状のリチウム含有遷移金属酸化物（１１）と平均直径１０ｎｍ〜５００ｎｍの平面状のグラファイト網（１２）が複数積層され、前記グラファイト網がファイバの縦軸に対して実質的に垂直であるカーボンナノファイバ（１３）を主成分とする導電性添加材料（１４）をそれぞれ含み、前記導電性添加材料（１４）に含まれるカーボンナノファイバ（１３）が１０００ｎｍ以上の長さと、１０以上のアスペクト比を有し、
前記導電性添加材料（１４）が活物質全体重量に対して０．５重量％〜１５重量％であることを特徴とする正極活物質。A plurality of particulate lithium-containing transition metal oxides (11) having an average particle diameter of 3 μm to 40 μm and a plurality of planar graphite nets (12) having an average diameter of 10 nm to 500 nm are laminated, and the graphite net is positioned with respect to the longitudinal axis of the fiber. Each of the conductive additive materials (14) includes a substantially vertical carbon nanofiber (13) as a main component, and the carbon nanofiber (13) included in the conductive additive material (14) has a length of 1000 nm or more. And having an aspect ratio of 10 or more,
The positive electrode active material, wherein the conductive additive material (14) accounts for 0.5% by weight to 15% by weight based on the total weight of the active material. 導電性添加材料（１４）はカーボンナノファイバ（１３）に加えて、更に黒鉛構造を有する炭素微粉からなる粒子状凝集体（１６）を含み、
前記カーボンナノファイバ（１３）が８０重量％〜９９．５重量％、前記粒子状凝集体（１６）が０．５重量％〜２０重量％の割合である請求項１記載の正極活物質。The conductive additive material (14) further includes, in addition to the carbon nanofibers (13), a particulate aggregate (16) made of carbon fine powder having a graphite structure,
The cathode active material according to claim 1, wherein the carbon nanofibers (13) are in a ratio of 80 wt% to 99.5 wt%, and the particulate aggregates (16) are in a ratio of 0.5 wt% to 20 wt%. 導電性添加材料（１４）に含まれるカーボンナノファイバ又は、カーボンナノファイバ及び粒子状凝集体をそれぞれ含む混合物のＸ線回折において測定されるグラファイト網（１２）平面の積層間隔ｄ００２が０．３３５４ｎｍ〜０．３３９ｎｍである請求項１又は２記載の正極活物質。The stacking interval d 002 of the plane of the graphite network (12) measured by X-ray diffraction of the carbon nanofibers or the mixture containing the carbon nanofibers and the particulate aggregates contained in the conductive additive material (14) is 0.3354 nm. The positive electrode active material according to claim 1, wherein the thickness is from 0.339 nm to 0.339 nm. 導電性添加材料（１４）に平均粒径１０ｎｍ〜５００ｎｍの金属又は金属酸化物（１７）のどちらか一方又はその双方を０．５重量％〜１０重量％更に含む請求項１ないし３いずれか１項に記載の正極活物質。The conductive additive material (14) further contains 0.5% by weight to 10% by weight of one or both of a metal and a metal oxide (17) having an average particle size of 10 nm to 500 nm. Item 7. The positive electrode active material according to item 1. カーボンナノファイバ（１３）の露出部又は、カーボンナノファイバ（１３）及び粒子状凝集体（１６）をそれぞれ含む混合物の露出部の少なくとも８５％がグラファイト網の端部である請求項１ないし４いずれか１項に記載の正極活物質。5. The graphite net according to claim 1, wherein at least 85% of the exposed portion of the carbon nanofibers or the exposed portion of the mixture containing the carbon nanofibers and the particulate agglomerates is the end of the graphite network. 4. The positive electrode active material according to claim 1. 金属又は金属酸化物のどちらか一方又はその双方がカーボンナノファイバの長軸上にある請求項１ないし５いずれか１項に記載の正極活物質。The positive electrode active material according to any one of claims 1 to 5, wherein one or both of the metal and the metal oxide are on the long axis of the carbon nanofiber. 金属がＦｅ、Ｃｏ、Ｎｉ、Ｍｇ、Ａｌ及びＭｎからなる群より選ばれた少なくとも１種の元素である請求項４又は６記載の正極活物質。7. The positive electrode active material according to claim 4, wherein the metal is at least one element selected from the group consisting of Fe, Co, Ni, Mg, Al, and Mn. 粒子状のリチウム含有遷移金属酸化物（１１）がＬｉＣｏＯ２、ＬｉＮｉＯ２及びＬｉＭｎ２Ｏ４からなる群より選ばれた少なくとも１種か、又は前記ＬｉＣｏＯ２、前記ＬｉＮｉＯ２及び前記ＬｉＭｎ２Ｏ４の組成の一部を金属元素で置換した非化学量論的化合物からなる群より選ばれた少なくとも１種のどちらか一方又は双方を含む請求項１記載の正極活物質。The particulate lithium-containing transition metal oxide (11) is at least one selected from the group consisting of LiCoO 2 , LiNiO 2, and LiMn 2 O 4 ; or the LiCoO 2 , LiNiO 2, and LiMn 2 O 4 The positive electrode active material according to claim 1, wherein the positive electrode active material includes at least one or both selected from the group consisting of non-stoichiometric compounds in which a part of the composition is substituted with a metal element. 導電性添加材料に粒子状の炭素系材料を更に含み、前記炭素系材料が石炭、コークス、ポリアクリロニトリル系炭素繊維、ピッチ系炭素繊維、有機物の炭素化品、天然黒鉛、人造黒鉛、合成黒鉛、メソカーボンマイクロビーズ、有機物の黒鉛化品及び黒鉛繊維からなる群より選ばれた少なくとも１種を含む請求項１ないし８いずれか１項に記載の正極活物質。The conductive additive material further includes a particulate carbon-based material, wherein the carbon-based material is coal, coke, polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, carbonized organic matter, natural graphite, artificial graphite, synthetic graphite, The positive electrode active material according to any one of claims 1 to 8, comprising at least one selected from the group consisting of mesocarbon microbeads, organic graphitized products, and graphite fibers. 請求項１ないし９いずれか１項に記載の正極活物質と、バインダとを用いて形成された正極。A positive electrode formed using the positive electrode active material according to any one of claims 1 to 9 and a binder. 請求項１０記載の正極を用いて形成されたリチウムイオン電池。A lithium ion battery formed using the positive electrode according to claim 10. 請求項１０記載の正極を用いて形成されたリチウムポリマー電池。A lithium polymer battery formed using the positive electrode according to claim 10.
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