JP4973826B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery - Google Patents
Method for producing positive electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery Download PDFInfo
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- JP4973826B2 JP4973826B2 JP2000347083A JP2000347083A JP4973826B2 JP 4973826 B2 JP4973826 B2 JP 4973826B2 JP 2000347083 A JP2000347083 A JP 2000347083A JP 2000347083 A JP2000347083 A JP 2000347083A JP 4973826 B2 JP4973826 B2 JP 4973826B2
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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
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Description
【０００１】
【産業上の利用分野】
本発明は、二次電池としての初期放電容量を維持し、且つ、高温下での充放電サイクル特性が改善された非水電解質二次電池を得ることができる正極活物質を提供する。
【０００２】
【従来の技術】
近年、ＡＶ機器やパソコン等の電子機器のポータブル化、コードレス化が急速に進んでおり、これらの駆動用電源として小型、軽量で高エネルギー密度を有する二次電池への要求が高くなっている。このような状況下において、充放電電圧が高く、充放電容量も大きいという長所を有するリチウムイオン二次電池が注目されている。
【０００３】
従来、４Ｖ級の電圧をもつ高エネルギー型のリチウムイオン二次電池に有用な正極活物質としては、スピネル型構造のＬｉＭｎ２Ｏ４、岩塩型構造のＬｉＭｎＯ２、ＬｉＣｏＯ２、ＬｉＣｏ１−ＸＮｉＸＯ２、ＬｉＮｉＯ２等が一般的に知られており、なかでもＬｉＣｏＯ２は高い充放電電圧と充放電容量を有する点で優れているが、更なる特性改善が求められている。
【０００４】
即ち、ノートパソコンなど二次電池で作動する装置はその使用に伴って高温になるため、二次電池として高温下での充放電サイクル特性に優れることが要求される。また、ＬｉＣｏＯ２は高い電圧で作動することができるが、高電圧のため電解液との反応が起こりやすく、充放電サイクル特性が低下しやすい。
【０００５】
そこで、高温下での充放電サイクル特性に優れたＬｉＣｏＯ２が要求されている。
【０００６】
従来、コバルト酸リチウム粒子粉末の諸特性改善のために、コバルト酸リチウム粒子表面をチタン化合物で被覆する方法（特開平４−３２９２６７号公報、特開平８−１０２３３２号公報、特開平２０００−２００６０５号公報等）、コバルト酸リチウム粒子中にチタンを含有させる方法（特開平６−４４９７４号公報等）、正極活物質としてコバルト酸リチウム粒子粉末とリチウムチタン複合酸化物（ＬｉＴｉ２Ｏ４）との混合物を用いる方法（特開平７−２８８１２４号公報）が知られており、また、コバルト酸リチウム粒子表面を、リン、ホウ素、酸化ジルコニウム、酸化サマリウムなどで被覆する方法（特許第３０５４８２９号公報、特許第３０４４８１２号公報、特許第２８５５８７７号公報、特許第３００３４３１号公報等）が知られている。
【０００７】
【発明が解決しようとする課題】
前記諸特性を満たす正極活物質は現在最も要求されいるところであるが、未だ得られていない。
【０００８】
即ち、前出特開平４−３２９２６７号公報には、コバルト酸リチウム粒子表面をチタンカップリング剤で表面処理した後、熱処理する方法が記載されているが、添加したチタン原子がコバルト酸リチウム粒子の内部方向に拡散して表面近傍にチタン添加表面層が形成されるため、電解液との反応を抑制する効果を得ることができず、高温下での充放電サイクル特性が十分とは言い難いものである。また、カップリング剤は高価なため工業的生産性に優れるとは言い難いものである。
【０００９】
前出特開平８−１０２３３２号公報には、コバルト酸リチウム粒子表面の一部にチタン酸化物などの低活性酸化物を分散保持させることが記載されているが、コバルト酸リチウム粒子表面に保持されているチタン酸化物の結合力が弱いので、高温下での充放電サイクル特性が十分とは言い難いものである。
【００１０】
前出特開平２０００−２００６０５号公報にはコバルト酸リチウム粒子表面にチタン粒子及び／又はチタン化合物粒子を付着させる方法が記載されているが、コバルト酸リチウム粒子とチタン化合物粒子とを乾式混合した場合には、チタン化合物粒子の混合が不均一となり付着するチタン化合物粒子の偏在箇所が発生するため、高温下での充放電サイクル特性が十分とは言い難いものである。
【００１１】
前出特開平６−４４９７４号公報にはリチウムコバルト酸化物とチタン酸化物との混合物を焼成してＬｉ１．４（Ｃｏ０．７Ｔｉ０．３）２Ｏ４を得る方法が記載されているが、初期充放電容量が低下し、また、電解液との反応を抑制する効果が得られないため、高温下での充放電サイクル特性が十分とは言い難いものである。
【００１２】
前出特開平７−２８８１２４号公報には、コバルト酸リチウム粒子粉末とリチウムチタン複合酸化物（ＬｉＴｉ２Ｏ４）との混合物を正極活物質として用いる方法が記載されているが、リチウムチタン酸複合酸化物を存在させるだけでは、電解液との反応を抑制する効果が得られないため、高温下での充放電サイクル特性が向上するとは言い難いものである。
【００１３】
また、前出チタン化合物以外の異種元素（リン、ホウ素、酸化ジルコニウム、酸化サマリウムなど）で被覆した場合には、電解液との反応を抑制することが困難なため、高温下での充放電サイクル特性が十分とは言い難いものである。
【００１４】
そこで、本発明は、初期放電容量に優れ、且つ、高温下での充放電サイクル特性に優れた正極活物質を得ることを技術的課題とする。
【００１５】
【課題を解決する為の手段】
前記技術的課題は、次の通りの本発明によって達成できる。
【００１６】
即ち、本発明は、非水電解質二次電池用正極活物質の製造法であって、コバルト酸リチウム粒子を分散させた水溶液のｐＨを調整し、次いでチタニウム塩を添加して、微細な水酸化チタニウムコロイドをコバルト酸リチウム粒子の粒子表面に吸着させた後、ろ過、水洗、乾燥して水酸化チタニウムコロイドを吸着させたコバルト酸リチウム粒子粉末を得、次いで、該コバルト酸リチウム粒子粉末を酸化雰囲気中、５００℃〜７００℃の温度範囲で熱処理して非水電解質二次電池用正極活物質を得るものであり、得られる非水電解質二次電池用正極活物質は、コバルト酸リチウム粒子粉末の粒子表面の一部に酸化チタン及び／又はチタン酸リチウムが被覆されており、前記酸化チタン及び／又はチタン酸リチウムの被覆量がコバルト酸リチウム粒子粉末中のコバルトに対しＴｉとして２．０〜４．０ｍｏｌ％であり、ＢＥＴ比表面積が０．１〜１．５ｍ２／ｇであることを特徴とする非水電解質二次電池用正極活物質の製造法である。
【００１８】
また、本発明は、前記非水電解質二次電池用正極活物質の製造方法によって得られた非水電解質二次電池用正極活物質を用いた非水電解質二次電池である。
【００１９】
本発明の構成をより詳しく説明すれば次の通りである。
【００２０】
先ず、本発明に係る正極活物質について述べる。
【００２１】
本発明に係る正極活物質は、コバルト酸リチウム粒子粉末の粒子表面の一部が酸化チタン及び／又はチタン酸リチウムで被覆されている。
【００２２】
本発明においては、酸化チタン及び／又はチタン酸リチウムはコバルト酸リチウム粒子粉末の粒子表面の一部を被覆しており、酸化チタン及び／又はチタン酸リチウムがコバルト酸リチウム粒子粉末の粒子表面全体を被覆した場合には、初期放電容量が低下する。酸化チタン及び／又はチタン酸リチウムの含有量はＴｉ換算でコバルト酸リチウム粒子粉末のコバルトに対して２．０〜４．０ｍｏｌ％である。２．０ｍｏｌ％以下の場合にはサイクル容量維持率向上の効果が小さく、４．０ｍｏｌ％を超える場合には初期放電容量が著しく低下する。好ましくは２．１〜３．５ｍｏｌ％、より好ましくは２．２〜３．０ｍｏｌ％である。
【００２３】
本発明に係る正極活物質の平均粒子径は１．０〜１０μｍが好ましい。平均粒子径が１．０μｍ未満の場合には、充填密度の低下や電解液との反応性が増加するため好ましくない。１０μｍを超える場合には、工業的に生産することが困難となる。
【００２４】
本発明に係る正極活物質のＢＥＴ比表面積は０．１〜１．５ｍ２／ｇが好ましい。ＢＥＴ比表面積値が０．１ｍ２／ｇ未満の場合には、工業的に生産することが困難となる。１．５ｍ２／ｇを超える場合には充填密度の低下や電解液との反応性が増加するため好ましくない。
【００２５】
本発明に係る正極活物質の格子定数はａ軸長が２．８１〜２．８２Å、ｃ軸長が１４．０４５〜１４．０６５Åであることが好ましい。
【００２６】
次に、本発明に係る正極活物質の製造法について述べる。
【００２７】
本発明に係る正極活物質は、コバルト酸リチウム粒子を分散させた水溶液にアルカリ塩を添加し、次いで、チタニウム塩を添加して微細な水酸化チタニウムコロイドをコバルト酸リチウムの粒子表面に吸着させ、ろ過、水洗、乾燥して水酸化チタニウムコロイドを吸着させたコバルト酸リチウム粒子粉末を得、次いで、該コバルト酸リチウム粒子粉末を酸化雰囲気中において５００〜７００℃で熱処理することで得られる。
【００２８】
本発明におけるコバルト酸リチウム粒子粉末は、通常の方法で得られるものであって、例えば、リチウム化合物とコバルト化合物を混合して加熱処理して得る固相法や、溶液中でリチウム化合物とコバルト化合物を反応させてコバルト酸リチウム粒子を得る湿式法のいずれの方法で得られたものでもよい。
【００２９】
コバルト酸リチウム粒子粉末は、平均粒子径が１．０〜１０μｍ、ＢＥＴ比表面積値が０．１〜１．５ｍ２／ｇ、Ｌｉ／Ｃｏ比が０．９５〜１．０５、格子定数がａ軸長２．８１〜２．８２Å、ｃ軸長１４．０４５〜１４．０６５Åであることが好ましい。
【００３０】
アルカリ塩としては、水酸化ナトリウム、水酸化カリウム、水酸化リチウム等を用いることができる。殊に、水酸化リチウムを用いた場合には、添加量と水洗度合いを調整することで、リチウムイオンを含有する水酸化チタニウムコロイドを得ることができ、熱処理を経ることでチタン酸リチウム又はチタン酸リチウムと酸化チタンとの混合物とすることができる。
【００３１】
アルカリ塩を添加した後に、チタニウム塩を添加する。
【００３２】
チタニウム塩としては、塩化チタン、硫酸チタン等を用いることができる。
【００３３】
チタニウム塩の添加量は、コバルト酸リチウム粒子粉末のコバルトに対して２．０〜４．０ｍｏｌ％であることが好ましい。
【００３４】
チタニウム塩を添加することによって水溶液のｐＨを１０．０〜１２．０にすることが好ましい。水溶液のｐＨが前記範囲外の場合には微細な水酸化チタニウムコロイドを生成・吸着させることが困難となる。
【００３５】
熱処理の雰囲気としては、酸化雰囲気であり、好ましくは大気中である。熱処理温度としては、５００〜７００℃であることが好ましい。５００℃未満の場合には水酸化チタニウム水和物が残存し、７００℃を超える場合には、粒子間の焼結が進行したり、チタン原子がコバルト酸リチウム粒子の内部方向に拡散するため好ましくない。保持時間は、１〜５時間が好ましい。１時間より短い場合には分解反応が不十分であり、５時間より長い場合には生産性とコストの面から好ましくない。
【００３６】
本発明に係る正極活物質を用いて正極を製造する場合には、常法に従って、導電剤と結着剤とを添加混合する。導電剤としてはアセチレンブラック、カーボンブラック、黒鉛等が好ましく、結着剤としてはポリテトラフルオロエチレン、ポリフッ化ビニリデン等が好ましい。
【００３７】
本発明に係る正極活物質を用いて二次電池を製造する場合には、前記正極、負極及び電解質から構成される。
【００３８】
負極活物質としては、リチウム金属、リチウム／アルミニウム合金、リチウム／スズ合金、グラファイトや黒鉛等を用いることができる。
【００３９】
また、電解液の溶媒としては、炭酸エチレンと炭酸ジエチルの組み合わせ以外に、炭酸プロピレン、炭酸ジメチル等のカーボネート類や、ジメトキシエタン等のエーテル類の少なくとも１種類を含む有機溶媒を用いることができる。
【００４０】
さらに、電解質としては、六フッ化リン酸リチウム以外に、過塩素酸リチウム、四フッ化ホウ酸リチウム等のリチウム塩の少なくとも１種類を上記溶媒に溶解して用いることができる。
【００４１】
本発明に係る正極活物質を用いて製造した二次電池は、初期放電容量が１４０〜１５０ｍＡｈ／ｇ、６０℃での５０サイクル後の容量維持率が９７％以上であり、過充電試験における充放電容量が低い。
【００４２】
【発明の実施の形態】
本発明の代表的な実施の形態は、次の通りである。
【００４３】
表面処理後および焼成後の生成物の同定については、粉末Ｘ線回折（ＲＩＧＡＫＵ Ｃｕ−Ｋα ４０ｋＶ ４０ｍＡ）を用いた。また、前記粉末Ｘ線回折の各々の回折ピークから格子定数を計算した。
【００４４】
また、元素分析にはプラズマ発光分析装置（セイコー電子工業製 ＳＰＳ４０００）を用いた。
【００４５】
正極活物質の電池特性は、下記製造法によって正極、負極及び電解液を調製しコイン型の電池セルを作製して評価した。
【００４６】
＜正極の作製＞
正極活物質と導電剤であるアセチレンブラック及び結着剤のポリフッ化ビニリデンを重量比で８５：１０：５となるように精秤し、乳鉢で十分に混合してからＮ−メチル−２−ピロリドンに分散させて正極合剤スラリーを調整した。次に、このスラリーを集電体のアルミニウム箔に１５０μｍの膜厚で塗布し、１５０℃で真空乾燥してからφ１６ｍｍの円板状に打ち抜き正極板とした。
【００４７】
＜負極の作製＞
金属リチウム箔をφ１６ｍｍの円板状に打ち抜いて負極を作製した。
【００４８】
＜電解液の調製＞
炭酸エチレンと炭酸ジエチルとの体積比５０：５０の混合溶液に電解質として六フッ化リン酸リチウム（ＬｉＰＦ６）を１モル／リットル混合して電解液とした。
【００４９】
＜コイン型電池セルの組み立て＞
アルゴン雰囲気のグローブボックス中でＳＵＳ３１６製のケースを用い、上記正極と負極の間にポリプロピレン製のセパレータを介し、さらに電解液を注入してＣＲ２０３２型のコイン電池を作製した。
【００５０】
＜電池評価＞
前記コイン型電池を用いて、二次電池の充放電試験を行った。測定条件としては、６０℃の温度下で、正極に対する電流密度を０．２ｍＡ／ｃｍ２とし、カットオフ電圧が３．０Ｖから４．２５Ｖの間で充放電を繰り返した。また、過充電試験については２０℃の温度下で４．９５Ｖまで充電を行った。
【００５１】
＜正極活物質の製造＞
リチウムとコバルトのモル比が１：１となるよう所定量の炭酸リチウムと酸化コバルトを十分に混合し、酸化雰囲気下、９００℃で１０時間焼成してコバルト酸リチウム粒子粉末を得た。
【００５２】
得られたコバルト酸リチウム粒子粉末は、平均長軸径が８．０μｍ、ＢＥＴ比表面積値が０．６ｍ２／ｇ、格子定数がａ軸２．８１７Å、ｃ軸１４．０５７Åであった。
【００５３】
次に、得られたコバルト酸リチウム粒子を水溶液中に分散させ、水酸化リチウムを投入した。次に、コバルトに対して２．５ｍｏｌ％のチタニウムを含有する四塩化チタンを投入して、溶液のｐＨを１２付近まで調整し、水洗、乾燥工程を経ることで、粒子表面にリチウムイオンを含む微細な水酸化チタニウムコロイドが吸着したコバルト酸リチウムを得た。次いで、得られた水酸化チタンコロイドが吸着したコバルト酸リチウム粒子を酸化雰囲気下、５００℃で５時間焼成することにより正極活物質を得た。
【００５４】
得られた正極活物質は、平均長軸径が８．０μｍ、ＢＥＴ比表面積値が０．５ｍ２／ｇ、格子定数がａ軸２．８１６Å、ｃ軸１４．０４９Å、チタンの含有量がコバルトに対して２．２０ｍｏｌ％であった。チタン含有量は添加量に対してほぼ全量が残存しており、且つ、焼成後の格子定数が被覆処理前と比較して変化しないことから、チタンはコバルト酸リチウムの格子中にドープされることなく、粒子表面上にチタン酸リチウムの状態で存在するものと推定できる。また、図１及び２に示すように、得られた正極活物質は処理前のコバルト酸リチウム粒子粉末のＸ線回折の回折パターンと同様であることから、酸化チタン及び／又はチタン酸リチウムは単相で存在することなく、コバルト酸リチウム粒子の表面に被覆されているものと推定できる。
【００５５】
前記正極活物質を用いて作製したコイン型電池は、初期放電容量が１５０ｍＡｈ／ｇ、６０℃での５０サイクル後の容量維持率が９７％／５０ｃｙｃｌｅ、過充電試験が２５０ｍＡｈ／ｇであった。
【００５６】
【作用】
本発明において最も重要な点は、本発明に係る正極活物質は、コバルト酸リチウム粒子表面の一部を酸化チタン及び／又はチタン酸リチウムで被覆することによって、二次電池としての初期放電容量を保持したまま、且つ、高温下での充放電サイクル特性に優れるという点である。
【００５７】
本発明においては、湿式反応によってコバルト酸リチウム粒子表面に直接微細な水酸化チタニウムコロイドを生成・吸着させて、次いで、酸化雰囲気中で熱処理することにより、微細な酸化チタン粒子及び／又はチタン酸リチウム粒子をコバルト酸リチウム粒子の粒子表面の一部に化学的に結合させている。
【００５８】
従って、コバルト酸リチウム粒子と酸化チタン粒子又はチタン酸リチウム粒子を乾式混合しただけの場合には、混合が不均一であったり互いの粒子が単なる物理吸着にすぎないため本発明の効果は得られない。また、水酸化チタニウム又はチタン酸リチウムと混合した後で熱処理した場合にも、均一な混合状態とならないため本発明の効果が得られない。
【００５９】
本発明において初期放電容量を保持できるのは、本来のコバルト酸リチウム粒子が有する初期放電容量を低下させない範囲で酸化チタン及び／又はチタン酸リチウムを含有させたことによる。
【００６０】
本発明において高温特性が改善できるのは、コバルト酸リチウム粒子の粒子表面の一部が酸化チタン及び／又はチタン酸リチウムで被覆した正極活物質を用いることにより、高温時（６０℃）又は４．８Ｖ以上の高電位で予想される粒子表面部のＣｏ（ＩＶ）と電解液の反応（酸化分解）が抑制されるためである。
【００６１】
【実施例】
次に、実施例並びに比較例を挙げる。
【００６２】
実施例１〜３、比較例１〜４
チタニウム塩の添加量、熱処理条件を種々変化させた以外は前記発明の実施の形態と同様にして正極活物質を製造し、次いでコイン型電池を製造した。
【００６３】
このときの製造条件を表１に、得られた正極活物質の諸特性及びコイン型電池の電池特性を表２に示す。
【００６４】
なお、比較例１では表面処理を行わなかった。比較例２及び３では熱処理を行わなかった。比較例４では熱処理条件を９００℃で行った。
【００６５】
【表１】
【表２】
本発明に係る正極活物質を用いて作製したコイン電池の電池特性は、初期放電容量が１４０ｍＡｈ／ｇ以上を保持し、６０℃での５０サイクル後の容量維持率が９７％以上と高いレベルにある。さらに、過充電試験においても被覆処理前の充電容量と比較するとその値が減少しており、正極活物質の粒子表面と電解液との反応抑制が示唆される。
【００６８】
また、比較例に示す通り、水酸化チタンを被覆しただけでは、過充電容量に極端な減少が確認されるものの、同時に初期放電容量も１２５ｍＡｈ／ｇ付近と低く、サイクル容量維持率についても改善効果が見られない。
【００６９】
【発明の効果】
本発明に係る正極活物質を用いることで、二次電池としての初期放電容量を維持し、且つ、高温特性が改善された非水電解質二次電池を得ることができる。
【図面の簡単な説明】
【図１】発明の実施の形態において、処理前のコバルト酸リチウム粒子粉末のＸ線回折パターン
【図２】発明の実施の形態で得られた正極活物質のＸ線回折パターン[0001]
[Industrial application fields]
The present invention provides a positive electrode active material capable of obtaining a nonaqueous electrolyte secondary battery that maintains an initial discharge capacity as a secondary battery and has improved charge / discharge cycle characteristics at high temperatures.
[0002]
[Prior art]
In recent years, electronic devices such as AV devices and personal computers are rapidly becoming portable and cordless, and there is an increasing demand for secondary batteries having a small size, light weight, and high energy density as power sources for driving these devices. Under such circumstances, a lithium ion secondary battery having advantages such as a high charge / discharge voltage and a large charge / discharge capacity has attracted attention.
[0003]
Conventionally, as a positive electrode active material useful for a high energy type lithium ion secondary battery having a voltage of 4 V class, spinel type structure LiMn 2 O 4 , rock salt type structure LiMnO 2 , LiCoO 2 , LiCo 1-X Ni X O 2 , LiNiO 2 and the like are generally known, and LiCoO 2 is excellent in that it has a high charge / discharge voltage and charge / discharge capacity, but further improvement in characteristics is required.
[0004]
That is, since a device that operates with a secondary battery such as a notebook computer becomes hot as it is used, it is required that the secondary battery has excellent charge / discharge cycle characteristics at high temperatures. In addition, LiCoO 2 can operate at a high voltage, but due to the high voltage, reaction with the electrolyte is likely to occur, and charge / discharge cycle characteristics are likely to deteriorate.
[0005]
Therefore, LiCoO 2 having excellent charge / discharge cycle characteristics at high temperatures is required.
[0006]
Conventionally, in order to improve various characteristics of lithium cobalt oxide particle powder, a method of coating the surface of lithium cobalt oxide particles with a titanium compound (JP-A-4-329267, JP-A-8-102332, JP-A-2000-200605). Publication, etc.), a method of incorporating titanium into lithium cobalt oxide particles (Japanese Patent Laid-Open No. 6-44974, etc.), and a mixture of lithium cobalt oxide particle powder and lithium titanium composite oxide (LiTi 2 O 4 ) as a positive electrode active material Is known (Japanese Patent Laid-Open No. 7-288124), and the surface of lithium cobaltate particles is coated with phosphorus, boron, zirconium oxide, samarium oxide, etc. (Japanese Patent No. 3054829, Patent No. (Japanese Patent No. 3044812, Japanese Patent No. 2855877, Japanese Patent No. 3003431) It has been known.
[0007]
[Problems to be solved by the invention]
A positive electrode active material that satisfies the above-mentioned properties is currently most demanded, but has not yet been obtained.
[0008]
That is, in the above-mentioned JP-A-4-329267, a method is described in which a lithium cobalt oxide particle surface is surface-treated with a titanium coupling agent and then heat-treated. Because the titanium-added surface layer is formed near the surface by diffusing in the internal direction, the effect of suppressing the reaction with the electrolyte cannot be obtained, and it is difficult to say that the charge / discharge cycle characteristics at high temperatures are not sufficient It is. Further, since the coupling agent is expensive, it is difficult to say that it is excellent in industrial productivity.
[0009]
In the above-mentioned JP-A-8-102332, it is described that a low activity oxide such as titanium oxide is dispersed and held on a part of the lithium cobalt oxide particle surface. Since the bonding strength of the titanium oxide is weak, it is difficult to say that the charge / discharge cycle characteristics at high temperatures are sufficient.
[0010]
In the above-mentioned JP 2000-2000605 A, a method of attaching titanium particles and / or titanium compound particles to the surface of lithium cobalt oxide particles is described, but when lithium cobalt oxide particles and titanium compound particles are dry mixed. In this case, uneven mixing of the titanium compound particles is generated, and unevenly distributed portions of the titanium compound particles to be adhered are generated. Therefore, it is difficult to say that the charge / discharge cycle characteristics at a high temperature are sufficient.
[0011]
JP-A-6-44974 mentioned above describes a method for obtaining Li 1.4 (Co 0.7 Ti 0.3 ) 2 O 4 by firing a mixture of lithium cobalt oxide and titanium oxide. However, since the initial charge / discharge capacity decreases and the effect of suppressing the reaction with the electrolytic solution cannot be obtained, it is difficult to say that the charge / discharge cycle characteristics at high temperatures are sufficient.
[0012]
In the above-mentioned JP-A-7-288124, a method of using a mixture of lithium cobaltate particles and lithium titanium composite oxide (LiTi 2 O 4 ) as a positive electrode active material is described. It is difficult to say that the charge / discharge cycle characteristics at high temperature are improved because the effect of suppressing the reaction with the electrolytic solution cannot be obtained only by the presence of the oxide.
[0013]
In addition, when it is coated with a different element (phosphorus, boron, zirconium oxide, samarium oxide, etc.) other than the above titanium compound, it is difficult to suppress the reaction with the electrolyte solution, so the charge / discharge cycle at high temperature It is hard to say that the characteristics are sufficient.
[0014]
Therefore, the present invention has a technical problem to obtain a positive electrode active material that is excellent in initial discharge capacity and excellent in charge / discharge cycle characteristics at high temperatures.
[0015]
[Means for solving the problems]
The technical problem can be achieved by the present invention as follows.
[0016]
That is, the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, in which the pH of an aqueous solution in which lithium cobaltate particles are dispersed is adjusted, and then a titanium salt is added to form a fine hydroxide. After adsorbing the titanium colloid on the surface of the lithium cobalt oxide particles, filtration, washing and drying to obtain lithium cobalt oxide particle powder adsorbing the titanium hydroxide colloid, and then the lithium cobalt oxide particle powder in an oxidizing atmosphere Among them, heat treatment is performed in a temperature range of 500 ° C. to 700 ° C. to obtain a positive electrode active material for a nonaqueous electrolyte secondary battery, and the obtained positive electrode active material for a nonaqueous electrolyte secondary battery is made of lithium cobalt oxide particle powder. Part of the particle surface is coated with titanium oxide and / or lithium titanate, and the coating amount of the titanium oxide and / or lithium titanate is lithium cobalt oxide A 2.0～4.0Mol% as Ti to cobalt in the child powder, the positive electrode active for a non-aqueous electrolyte secondary battery, wherein a BET specific surface area of 0.1~1.5m 2 / g It is a manufacturing method of a substance.
[0018]
Moreover, this invention is a nonaqueous electrolyte secondary battery using the positive electrode active material for nonaqueous electrolyte secondary batteries obtained by the manufacturing method of the said positive electrode active material for nonaqueous electrolyte secondary batteries.
[0019]
The configuration of the present invention will be described in more detail as follows.
[0020]
First, the positive electrode active material according to the present invention will be described.
[0021]
In the positive electrode active material according to the present invention, a part of the particle surface of the lithium cobalt oxide particle powder is coated with titanium oxide and / or lithium titanate.
[0022]
In the present invention, the titanium oxide and / or lithium titanate covers a part of the particle surface of the lithium cobaltate particle powder, and the titanium oxide and / or lithium titanate covers the entire particle surface of the lithium cobaltate particle powder. In the case of coating, the initial discharge capacity decreases. Content of a titanium oxide and / or lithium titanate is 2.0-4.0 mol% with respect to cobalt of lithium cobaltate particle powder in Ti conversion. When the amount is 2.0 mol% or less, the effect of improving the cycle capacity retention rate is small, and when it exceeds 4.0 mol%, the initial discharge capacity is remarkably reduced. Preferably it is 2.1-3.5 mol%, More preferably, it is 2.2-3.0 mol%.
[0023]
The average particle diameter of the positive electrode active material according to the present invention is preferably 1.0 to 10 μm. An average particle size of less than 1.0 μm is not preferable because the packing density is lowered and the reactivity with the electrolytic solution is increased. When it exceeds 10 μm, it is difficult to produce industrially.
[0024]
The BET specific surface area of the positive electrode active material according to the present invention is preferably 0.1 to 1.5 m 2 / g. When the BET specific surface area value is less than 0.1 m 2 / g, it is difficult to produce industrially. If it exceeds 1.5 m 2 / g, the filling density is lowered and the reactivity with the electrolytic solution is increased.
[0025]
As for the lattice constant of the positive electrode active material according to the present invention, the a-axis length is preferably 2.81 to 2.82 mm and the c-axis length is preferably 14.451 to 14.065 mm.
[0026]
Next, a method for producing the positive electrode active material according to the present invention will be described.
[0027]
In the positive electrode active material according to the present invention, an alkali salt is added to an aqueous solution in which lithium cobaltate particles are dispersed, and then a titanium salt is added to adsorb fine titanium hydroxide colloids to the lithium cobaltate particle surface, It is obtained by filtering, washing with water and drying to obtain lithium cobaltate particle powder adsorbing titanium hydroxide colloid, and then heat-treating the lithium cobaltate particle powder at 500 to 700 ° C. in an oxidizing atmosphere.
[0028]
The lithium cobalt oxide particle powder in the present invention is obtained by a usual method. For example, a solid phase method obtained by mixing and heat-treating a lithium compound and a cobalt compound, or a lithium compound and a cobalt compound in a solution. It may be obtained by any method of the wet method in which lithium cobaltate particles are obtained by reacting.
[0029]
The lithium cobalt oxide particle powder has an average particle size of 1.0 to 10 μm, a BET specific surface area value of 0.1 to 1.5 m 2 / g, a Li / Co ratio of 0.95 to 1.05, and a lattice constant of a It is preferable that the axial length is 2.81 to 2.82 mm and the c-axis length is 14.045 to 14.065 mm.
[0030]
As the alkali salt, sodium hydroxide, potassium hydroxide, lithium hydroxide or the like can be used. In particular, when lithium hydroxide is used, a titanium hydroxide colloid containing lithium ions can be obtained by adjusting the addition amount and the degree of washing with water, and lithium titanate or titanate can be obtained through heat treatment. It can be a mixture of lithium and titanium oxide.
[0031]
After adding the alkali salt, the titanium salt is added.
[0032]
As the titanium salt, titanium chloride, titanium sulfate or the like can be used.
[0033]
The addition amount of the titanium salt is preferably 2.0 to 4.0 mol% with respect to the cobalt of the lithium cobalt oxide particle powder.
[0034]
It is preferable to adjust the pH of the aqueous solution to 10.0 to 12.0 by adding a titanium salt. When the pH of the aqueous solution is outside the above range, it becomes difficult to generate and adsorb fine titanium hydroxide colloid.
[0035]
The atmosphere for the heat treatment is an oxidizing atmosphere, preferably in the air. The heat treatment temperature is preferably 500 to 700 ° C. When the temperature is lower than 500 ° C., titanium hydroxide hydrate remains, and when the temperature exceeds 700 ° C., sintering between particles proceeds or titanium atoms diffuse in the internal direction of the lithium cobalt oxide particles. Absent. The holding time is preferably 1 to 5 hours. When it is shorter than 1 hour, the decomposition reaction is insufficient, and when it is longer than 5 hours, it is not preferable from the viewpoint of productivity and cost.
[0036]
When a positive electrode is produced using the positive electrode active material according to the present invention, a conductive agent and a binder are added and mixed according to a conventional method. As the conductive agent, acetylene black, carbon black, graphite and the like are preferable, and as the binder, polytetrafluoroethylene, polyvinylidene fluoride and the like are preferable.
[0037]
When manufacturing a secondary battery using the positive electrode active material which concerns on this invention, it is comprised from the said positive electrode, a negative electrode, and electrolyte.
[0038]
As the negative electrode active material, lithium metal, lithium / aluminum alloy, lithium / tin alloy, graphite, graphite, or the like can be used.
[0039]
In addition to the combination of ethylene carbonate and diethyl carbonate, an organic solvent containing at least one of carbonates such as propylene carbonate and dimethyl carbonate and ethers such as dimethoxyethane can be used as the solvent for the electrolytic solution.
[0040]
Further, as the electrolyte, in addition to lithium hexafluorophosphate, at least one lithium salt such as lithium perchlorate and lithium tetrafluoroborate can be dissolved in the above solvent and used.
[0041]
The secondary battery manufactured using the positive electrode active material according to the present invention has an initial discharge capacity of 140 to 150 mAh / g, a capacity maintenance rate of 50% after 50 cycles at 60 ° C., and is charged in an overcharge test. Discharge capacity is low.
[0042]
DETAILED DESCRIPTION OF THE INVENTION
A typical embodiment of the present invention is as follows.
[0043]
Powder X-ray diffraction (RIGAKU Cu-Kα 40 kV 40 mA) was used for identification of the product after the surface treatment and after firing. The lattice constant was calculated from each diffraction peak of the powder X-ray diffraction.
[0044]
In addition, a plasma emission analyzer (SEPS Electronics SPS4000) was used for elemental analysis.
[0045]
The battery characteristics of the positive electrode active material were evaluated by preparing a positive electrode, a negative electrode, and an electrolytic solution by the following production method to produce a coin-type battery cell.
[0046]
<Preparation of positive electrode>
A positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are precisely weighed so that the weight ratio is 85: 10: 5, and thoroughly mixed in a mortar, and then N-methyl-2-pyrrolidone. The positive electrode mixture slurry was prepared by dispersing in the mixture. Next, this slurry was applied to an aluminum foil as a current collector with a film thickness of 150 μm, vacuum-dried at 150 ° C., and then punched into a disk shape of φ16 mm to obtain a positive electrode plate.
[0047]
<Production of negative electrode>
A metal lithium foil was punched into a disk shape of φ16 mm to produce a negative electrode.
[0048]
<Preparation of electrolyte>
An electrolyte solution was prepared by mixing 1 mol / liter of lithium hexafluorophosphate (LiPF 6 ) as an electrolyte in a mixed solution of ethylene carbonate and diethyl carbonate in a volume ratio of 50:50.
[0049]
<Assembly of coin-type battery cells>
Using a case made of SUS316 in a glove box in an argon atmosphere, a CR2032-type coin battery was manufactured by injecting an electrolyte solution through a polypropylene separator between the positive electrode and the negative electrode.
[0050]
<Battery evaluation>
A charge / discharge test of a secondary battery was performed using the coin-type battery. As measurement conditions, under a temperature of 60 ° C., the current density with respect to the positive electrode was set to 0.2 mA / cm 2, and charging / discharging was repeated between a cutoff voltage of 3.0 V and 4.25 V. Moreover, about the overcharge test, it charged to 4.95V under the temperature of 20 degreeC.
[0051]
<Manufacture of positive electrode active material>
A predetermined amount of lithium carbonate and cobalt oxide were sufficiently mixed so that the molar ratio of lithium to cobalt was 1: 1, and calcined at 900 ° C. for 10 hours in an oxidizing atmosphere to obtain lithium cobalt oxide particle powder.
[0052]
The obtained lithium cobalt oxide particle powder had an average major axis diameter of 8.0 μm, a BET specific surface area value of 0.6 m 2 / g, lattice constants of a-axis 2.817Å, and c-axis 14.057Å.
[0053]
Next, the obtained lithium cobaltate particles were dispersed in an aqueous solution, and lithium hydroxide was added. Next, titanium tetrachloride containing 2.5 mol% of titanium with respect to cobalt is added, the pH of the solution is adjusted to around 12, and the surface of the particles contains lithium ions through water washing and drying processes. A lithium cobaltate adsorbed with fine titanium hydroxide colloid was obtained. Next, the obtained lithium cobalt oxide particles adsorbed with the titanium hydroxide colloid were fired in an oxidizing atmosphere at 500 ° C. for 5 hours to obtain a positive electrode active material.
[0054]
The obtained positive electrode active material had an average major axis diameter of 8.0 μm, a BET specific surface area value of 0.5 m 2 / g, lattice constants of a-axis 2.816Å, c-axis 14.049Å, and a titanium content of cobalt. It was 2.20 mol% with respect to this. Titanium is doped in the lattice of lithium cobaltate because almost all of the titanium content remains with respect to the added amount and the lattice constant after firing does not change compared to before the coating treatment. It can be presumed that it exists in the state of lithium titanate on the particle surface. Further, as shown in FIGS. 1 and 2, since the obtained positive electrode active material has the same X-ray diffraction pattern as that of the lithium cobalt oxide particle powder before the treatment, titanium oxide and / or lithium titanate is single. It can be presumed that the surface of the lithium cobalt oxide particles is coated without being present in a phase.
[0055]
The coin-type battery manufactured using the positive electrode active material had an initial discharge capacity of 150 mAh / g, a capacity retention rate after 50 cycles at 60 ° C. of 97% / 50 cycle, and an overcharge test of 250 mAh / g.
[0056]
[Action]
The most important point in the present invention is that the positive electrode active material according to the present invention has an initial discharge capacity as a secondary battery by covering a part of the lithium cobalt oxide particle surface with titanium oxide and / or lithium titanate. It is the point which is excellent in the charge / discharge cycle characteristic in high temperature with hold | maintaining.
[0057]
In the present invention, fine titanium hydroxide colloids are generated and adsorbed directly on the surface of lithium cobalt oxide particles by wet reaction, and then heat-treated in an oxidizing atmosphere to thereby produce fine titanium oxide particles and / or lithium titanate. The particles are chemically bonded to a part of the particle surface of the lithium cobalt oxide particles.
[0058]
Therefore, when lithium cobalt oxide particles and titanium oxide particles or lithium titanate particles are only dry mixed, the effects of the present invention can be obtained because the mixing is not uniform or the particles are merely physisorption. Absent. In addition, even when heat treatment is performed after mixing with titanium hydroxide or lithium titanate, the effect of the present invention cannot be obtained because a uniform mixed state is not obtained.
[0059]
The reason why the initial discharge capacity can be maintained in the present invention is that titanium oxide and / or lithium titanate is contained within a range that does not reduce the initial discharge capacity of the original lithium cobalt oxide particles.
[0060]
In the present invention, the high temperature characteristics can be improved by using a positive electrode active material in which a part of the particle surface of the lithium cobalt oxide particles is coated with titanium oxide and / or lithium titanate, at a high temperature (60 ° C.) or This is because the reaction (oxidative decomposition) between Co (IV) and the electrolyte solution on the particle surface, which is expected at a high potential of 8 V or more, is suppressed.
[0061]
【Example】
Next, examples and comparative examples are given.
[0062]
Examples 1-3, Comparative Examples 1-4
A positive electrode active material was produced in the same manner as in the above embodiment except that the amount of titanium salt added and various heat treatment conditions were changed, and then a coin-type battery was produced.
[0063]
The production conditions at this time are shown in Table 1, and the characteristics of the obtained positive electrode active material and the battery characteristics of the coin-type battery are shown in Table 2.
[0064]
In Comparative Example 1, no surface treatment was performed. In Comparative Examples 2 and 3, no heat treatment was performed. In Comparative Example 4, the heat treatment condition was 900 ° C.
[0065]
[Table 1]
[Table 2]
The battery characteristics of the coin battery manufactured using the positive electrode active material according to the present invention are such that the initial discharge capacity is maintained at 140 mAh / g or more, and the capacity retention rate after 50 cycles at 60 ° C. is as high as 97% or more. is there. Furthermore, in the overcharge test, the value is reduced as compared with the charge capacity before the coating treatment, suggesting that the reaction between the particle surface of the positive electrode active material and the electrolytic solution is suppressed.
[0068]
In addition, as shown in the comparative example, only by covering with titanium hydroxide, an excessive decrease in overcharge capacity is confirmed, but at the same time, the initial discharge capacity is as low as around 125 mAh / g, and the cycle capacity maintenance rate is also improved. Is not seen.
[0069]
【Effect of the invention】
By using the positive electrode active material according to the present invention, it is possible to obtain a nonaqueous electrolyte secondary battery that maintains an initial discharge capacity as a secondary battery and has improved high-temperature characteristics.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of a lithium cobalt oxide particle powder before treatment in an embodiment of the invention. FIG. 2 is an X-ray diffraction pattern of a positive electrode active material obtained in the embodiment of the invention.
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000347083A JP4973826B2 (en) | 2000-11-14 | 2000-11-14 | Method for producing positive electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000347083A JP4973826B2 (en) | 2000-11-14 | 2000-11-14 | Method for producing positive electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2002151078A JP2002151078A (en) | 2002-05-24 |
| JP4973826B2 true JP4973826B2 (en) | 2012-07-11 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP4553095B2 (en) * | 2002-05-29 | 2010-09-29 | 戸田工業株式会社 | Cobalt oxide particle powder and production method thereof, positive electrode active material for non-aqueous electrolyte secondary battery, production method thereof, and non-aqueous electrolyte secondary battery |
| TWI286849B (en) | 2003-03-25 | 2007-09-11 | Nichia Corp | Positive electrode active material for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery |
| KR100644915B1 (en) | 2005-01-21 | 2006-11-10 | 주식회사 이엔켐 | Cathode active material for a Lithium secondary battery and a Lithium secondary battery containing the same |
| CN1855587B (en) * | 2005-04-28 | 2010-05-05 | 比亚迪股份有限公司 | Battery anode preparation method and preparation method of lithium ion batteries using the battery anode |
| JP5076301B2 (en) * | 2005-10-07 | 2012-11-21 | ソニー株式会社 | Secondary battery |
| JP5176317B2 (en) * | 2006-12-26 | 2013-04-03 | 住友金属鉱山株式会社 | Cathode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery using the same |
| KR101160110B1 (en) | 2007-11-01 | 2012-06-27 | 에이지씨 세이미 케미칼 가부시키가이샤 | Process for production of positive electrode active material for lithium ion secondary battery |
| JP5126834B2 (en) * | 2008-03-12 | 2013-01-23 | 独立行政法人産業技術総合研究所 | Composite of metal sulfide and metal oxide and method for producing the same |
| WO2010090185A1 (en) | 2009-02-05 | 2010-08-12 | Ａｇｃセイミケミカル株式会社 | Surface-modified lithium-containing complex oxide for positive electrode active material for lithium ion secondary battery, and method for producing same |
| JP5673990B2 (en) * | 2009-07-24 | 2015-02-18 | 日産自動車株式会社 | Positive electrode material for lithium ion battery and lithium ion battery using the same |
| CN102576872A (en) | 2009-10-05 | 2012-07-11 | 日本化学工业株式会社 | Positive electrode active material for lithium secondary battery, method for manufacturing the same, and lithium secondary battery |
| FR2980042B1 (en) * | 2011-09-09 | 2014-10-24 | Commissariat Energie Atomique | METHOD FOR MANUFACTURING ELECTRODE AND INK FOR ELECTRODE |
| WO2014020729A1 (en) | 2012-08-01 | 2014-02-06 | トヨタ自動車株式会社 | Non-aqueous electrolyte solution secondary battery |
| KR101937899B1 (en) | 2015-12-23 | 2019-01-14 | 주식회사 엘지화학 | Positive electrode active material for secondary battery and secondary battery comprising the same |
| WO2021024789A1 (en) * | 2019-08-05 | 2021-02-11 | パナソニック株式会社 | Positive electrode active material for nonaqueous electrolyte secondary batteries, and nonaqueous electrolyte secondary battery |
| JP7208274B2 (en) * | 2021-01-20 | 2023-01-18 | プライムプラネットエナジー＆ソリューションズ株式会社 | Positive electrode active material and non-aqueous electrolyte secondary battery using the positive electrode active material |
| CN113443655B (en) * | 2021-06-28 | 2023-06-23 | 天目湖先进储能技术研究院有限公司 | Layered composite oxide coated positive electrode material and preparation method and application thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP3438339B2 (en) * | 1994-08-09 | 2003-08-18 | 住友電気工業株式会社 | Metal oxide coating method and metal oxide coating |
| JPH08183605A (en) * | 1994-12-28 | 1996-07-16 | Dainippon Printing Co Ltd | Production of metal oxide film by coating |
| JP2000200605A (en) * | 1998-10-30 | 2000-07-18 | Sanyo Electric Co Ltd | Nonaqueous electrolyte battery and its manufacture |
| JP2000164214A (en) * | 1998-11-25 | 2000-06-16 | Japan Storage Battery Co Ltd | Now-aqueous electrolyte secondary battery |
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