JP3706718B2 - Lithium ion secondary battery positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery - Google Patents
Lithium ion secondary battery positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery Download PDFInfo
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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】
【発明の属する技術分野】
本発明は、リチウムイオン二次電池用コバルト酸リチウム系正極活物質、この製造方法及びこれを含有する正極材を用いるリチウムイオン二次電池に関する。
【０００２】
【技術の技術】
近年、家庭電器においてポータブル化、コードレス化が急速に進むに従い、ラップトップ型パソコン、携帯電話、ビデオカメラ等の小型電子機器の電源としてリチウムイオン二次電池が実用化されている。このリチウムイオン二次電池については、１９８０年に水島等によりコバルト酸リチウムがリチウムイオン二次電池の正極活物質として有用であるとの報告（「マテリアル リサーチブレティン」vo115,P783-789(1980)）がなされて以来、コバルト酸リチウム系正極活物質に関する研究開発が活発に進められており、これまで多くの提案がなされている。
【０００３】
従来、正極活物質の高エネルギー密度化を図る技術としては、例えばコバルト酸リチウムの組成をＬｉｘＣｏＯ2 （但し、1.05≦ｘ≦1.3 ）とすることによりリチウムリッチにしたもの（特開平３−127454号公報）、逆にＬｉｘＣｏＯ2 （但し０＜ｘ≦１）とすることによってコバルトリッチにしたもの（特開平3-134969号公報）、Ｍｎ、Ｗ、Ｎｉ、Ｌａ、Ｚｒなどの金属イオンをドープさせたもの（特開平3-201368号公報、特開平4-328277号公報、特開平4-319259号公報、特開平4-319260号公報等）、コバルト酸リチウム中の残留Ｌｉ2 ＣＯ3 を１０重量％以下としたもの（特開平4-56064 号公報）などが提案されている。
【０００４】
一方、コバルト酸リチウム系正極活物質の物理的特徴、特に比表面積を要件とする技術としては、ＬｉＣｏＯ2 の比表面積を２ｍ2 /g以下（特開平4-56064 号公報）、リチウム複合酸化物の比表面積を0.01〜3.0 ｍ2 /g（特開平4-249073号公報）、Ｌｉx Ｃｏy Ｏ2 (0＜ｘ≦1.3 、1.8 ≦y ≦2.2)のBET 法による比表面積が0.5 〜10.0ｍ2 /g（特開平6-103976号公報）等を有するコバルト酸リチウムを用いることにより、放電サイクルの進行に伴う放電容量の低下を改善できることが提案されている。
【０００５】
また、ＬｉＣｏＯ2 をアモルファスとするもの（特開平5-21066 号公報）、ＬｉＣｏＯ2 に一定の粒度特性を与えるもの（特開平4-33260 号公報、特開平5-94822 号公報）、ＬｉＣｏＯ2 を特定のＸ線回折強度をもつ結晶粒子とするもの（特開平3-272564号公報、特開平5-36414 号公報）等が知られている。また、コバルト酸リチウム系正極活物質の製造方法については、特開平3-285262号公報、特開平4-249074号公報、特開平4-123762号公報、特開平5-54886 号公報、特開平5-54888 号公報、特開平5-62678 号公報、特開平5-182667号公報などに多数の提案がなされている。
【０００６】
【発明が解決しようとする課題】
しかしながら、リチウムイオン二次電池の正極活物質として用いられるコバルト酸リチウムは、例えば炭酸リチウムのようなリチウム塩と酸化コバルトなどのコバルト化合物をＬｉ／Ｃｏの原子比が０．９〜１．２の範囲になるように混合し、該混合物を６００〜１１００℃の温度条件で焼成することによって製造されるが、得られるコバルト酸リチウムの物性が製造条件により微妙に変化し、電池としての放電特性や放電サイクル特性等正極活物質の性能に著しい影響を与え、この結果、従来のコバルト酸リチウムを正極活物質とするリチウムイオン二次電池は安定した十分な性能を発揮しているとは言いがたいものであった。
【０００７】
従って、本発明の目的は、エネルギー密度の高いコバルト酸リチウム系正極活物質及び安定に優れた放電容量及びサイクル特性を示す二次電池を提供することにある。
【０００８】
【課題を解決するための手段】
かかる実情において、本発明者は鋭意検討を行った結果、リチウム二次電池用正極活物質として好適なコバルト酸リチウム中に含まれる水分量が特定値以下であり、高い湿度状態においても吸湿しずらく、また、コバルトの酸化数が特定の範囲に制御されているものが、放電容量及び放電保持率に優れ、高いエネルギー密度を与えることを見出し、本発明を完成するに至った。
すなわち、本発明は、リチウムイオン二次電池用コバルト酸リチウム系正極活物質において、該コバルト酸リチウムを室温放置後、次いでカールフィッシャー滴定法による１２０℃水分気化法での水分測定量（Ａ）が１５０ppm 以下及び／又は該コバルト酸リチウムを３０℃、相対湿度６０％、１２時間放置後、次いでカールフィッシャー滴定法による１２０℃水分気化法での水分測定量（Ｂ）が２００ppm 以下であることを特徴とするリチウムイオン二次電池用コバルト酸リチウム系正極活物質を提供するものである。
【０００９】
また、本発明は、リチウムイオン二次電池用コバルト酸リチウム系正極活物質において、該コバルト酸リチウムを室温放置後、次いでカールフィッシャー滴定法による１２０℃水分気化法での水分測定量（Ａ）と、次いで測定される２５０℃水分気化法での水分測定量（Ｃ）とにおいて、（Ａ＋Ｃ）値が３００ppm 以下及びＡ値が１５０ppm 以下であることを特徴とするリチウム二次電池用コバルト酸リチウム系正極活物質を提供するものである。
【００１０】
また、本発明は、リチウムイオン二次電池用コバルト酸リチウム系正極活物質において、該コバルト酸リチウムを１２０°Ｃで２時間乾燥後、次いでカールフィッシャー滴定法による２５０℃水分気化法での水分測定量（Ｄ）が１００ppm 以下であることを特徴とするリチウム二次電池用コバルト酸リチウム系正極活物質を提供するものである。
【００１１】
また、本発明は、リチウムイオン二次電池用コバルト酸リチウム系正極活物質において、該コバルト酸リチウムを１２０°Ｃで２時間乾燥後、次いで２５０°Ｃで２時間焼成し、冷却した後、次いで該コバルト酸リチウムを３０°Ｃ、相対湿度６０％、１２時間放置後、さらに１２０°Ｃで２時間乾燥後、カールフィッシャー滴定法による２５０℃水分気化法での水分測定量（Ｅ）が５０ppm 以下であることを特徴とするリチウム二次電池用コバルト酸リチウム系正極活物質を提供するものである。
【００１２】
また、本発明は、コバルト酸リチウム中のコバルト酸化数が、電位差滴定法で２．９０〜３．１０であるリチウムイオン二次電池用コバルト酸リチウム系正極活物質を提供するものである。
【００１３】
また、本発明は、炭酸リチウムと酸化コバルトとを混合して、次いで焼成、冷却、粉砕してコバルト酸リチウムを製造する方法において、少なくとも前記冷却及び粉砕の各処理工程において絶対湿度２０g/kg' 以下の空気を吹き込みながら各処理操作を行うことを特徴とするリチウムイオン二次電池用コバルト酸リチウム系正極活物質の製造方法を提供するものである。
【００１４】
また、本発明は、炭酸リチウムと酸化コバルトとを混合して、次いで焼成、冷却、粉砕してコバルト酸リチウムを製造する方法において、少なくとも前記冷却及び粉砕の各処理工程において絶対湿度２０g/kg' 以下の空気を吹き込みながら各処理操作を行い、該処理操作を再度繰り返して行うことを特徴とするリチウムイオン二次電池用コバルト酸リチウム系正極活物質の製造方法を提供するものである。
【００１５】
また、本発明は、前記リチウムイオン二次電池用コバルト酸リチウム系正極活物質を含有する正極材を用いることを特徴とするリチウムイオン二次電池を提供するものである。
【００１６】
【発明の実施の形態】
本発明のリチウムイオン二次電池用コバルト酸リチウム系正極活物質において、該コバルト酸リチウムを室温放置後、次いでカールフィッシャー滴定法（以下、単に「ＫＦ法」ということもある。）による１２０℃水分気化法での水分測定量（Ａ）値が１５０ppm 以下であり、好ましくは１００ppm 以下である。また、該コバルト酸リチウムを３０℃、相対湿度６０％、１２時間放置後、次いでＫＦ法による１２０℃水分気化法での水分測定量（Ｂ）値が２００ppm 以下であり、好ましくは１５０ppm 以下である。また、上記（Ａ）値と（Ｂ）値の差（Ｂ−Ａ）が５０ppm 以下であることが好ましい。すなわち、本発明のコバルト酸リチウムは、該コバルト酸リチウム中に含まれる水分量を特定量以下とし、かつ特定の湿度雰囲気下でも吸湿しにくい、水分に対して極めて安定な化合物であることが重要な物性となるものである。上記（Ａ）値が１５０ppm の水分量を超え、かつ（Ｂ）値が２００ppm を超えるものを正極材として使用すると電解液を分解し、二次電池特性の低下を招く結果となり好ましくない。
【００１７】
前記ＫＦ法による１２０℃水分気化法の水分測定方法としては、特に制限されず、公知の方法に従えばよく、例えば、市販のカールフィッシャー水分計と水分気化装置を組み合わせて用いればよい。すなわち、試料を該水分気化装置にセッティング後、１２０℃の加熱条件下で発生する気化した水分をキャリアガスの乾燥窒素とともに捕集し、これをカールフィッシャ水分計に導入し、水分量を測定すればよい。
【００１８】
また、室温放置条件としては、約２０〜２５℃の温度、相対湿度２０〜５０％の条件下に放置するものである。
【００１９】
また、本発明において、リチウムイオン二次電池用コバルト酸リチウム系正極活物質における該コバルト酸リチウムを室温放置後、次いでＫＦ法による１２０℃水分気化法での水分測定量（Ａ）と、次いで測定される２５０℃水分気化法での水分測定量（Ｃ）とにおいて、（Ａ＋Ｃ）値が３００ppm 以下及びＡ値が１５０ppm 以下である。（Ａ＋Ｃ）値の好ましい範囲は、１５０ppm 以下であり、Ａ値の好ましい範囲は１００ppm 以下である。
【００２０】
また、本発明において、リチウムイオン二次電池用コバルト酸リチウム系正極活物質における該コバルト酸リチウムを１２０°Ｃで２時間乾燥後、次いでカールフィッシャー滴定法による２５０℃水分気化法での水分測定量（Ｄ）が１００ppm 以下である。（Ｄ）値の好ましい範囲は、５０ppm 以下である。
【００２１】
また、本発明において、リチウムイオン二次電池用コバルト酸リチウム系正極活物質において、該コバルト酸リチウムを１２０°Ｃで２時間乾燥後、次いで２５０°Ｃで２時間焼成し、冷却した後、次いで該コバルト酸リチウムを３０°Ｃ、相対湿度６０％、１２時間放置後、さらに１２０°Ｃで２時間乾燥後、カールフィッシャー滴定法による２５０℃水分気化法での水分測定量（Ｅ）が５０ppm 以下である。
【００２２】
前記ＫＦ法による２５０℃水分気化法による測定方法としては、１２０℃を２５０℃とする以外は前記ＫＦ法による１２０℃水分気化法による測定方法と同様にして行えばよい。この１２０℃と２５０℃との加熱温度の違いによる留出水分のメカニズムは、明確ではないが、１２０℃加熱条件下の場合、該粒子表面に物理的に吸着している水分が留出し、更に２５０℃に昇温した場合は、該粒子の結晶構造に起因する微細な細孔内に化学的に吸着している水分が留出してくるものと考えられる。上記数値を超えた粒子をリチウムイオン二次電池の正極活物質に使用する場合、表面に付着している水分ばかりでなく、長いサイクルを経るとその結晶粒子内から徐々に水分が留出して、初期容量及びサイクル特性等の電池特性の低下を招く結果となり、好ましくない。すなわち、粒子表面の水分のみでなく結晶粒子内に吸着している水分も極めて少ないものが好ましく、かかる化合物をリチウムイオン二次電池用正極活物質として使用することにより優れた電池特性を有することができる。
【００２３】
また、本発明のコバルト酸リチウム系正極活物質は、コバルト酸リチウム中のコバルトの酸化数が電位差滴定法による測定で２．９０〜３．１０、好ましくは２．９５〜３．０５の範囲のものが好ましい。通常、コバルト酸リチウム（LiCoO2）組成式中のコバルトの酸化数は、３価が理論的であるが、その製造方法により化合物中のコバルトの酸化数が常に理論的な数値になることはなく、その理論価数から大きくずれることもある。このコバルトの酸化数が変わることにより、結晶構造に歪みが生じ、これをリチウムイオン二次電池の正極材として使用し充放電を繰り返すと、サイクル特性等の電池特性が低下するので好ましくない。
【００２４】
本発明において、前記リチウムイオン二次電池用コバルトリチウム系正極活物質を製造する方法は、炭酸リチウムと酸化コバルトを混合して、次いで焼成し、冷却、粉砕する方法において、少なくとも該冷却及び粉砕の各処理工程、好ましくは該焼成、冷却及び粉砕の各処理工程において、絶対湿度２０ｇ／kg' 以下の空気を吹き込みながら各処理操作を行えばよい。例えば、炭酸リチウムと酸化コバルトを、Ｌｉ／Ｃｏの原子比として１付近、好ましくは０．９９〜１．１０になる範囲の配合割合で混合する。次いで、絶対湿度２０ｇ／kg' 以下の空気を吹き込みながら混合物を６００℃〜１１００℃、好ましくは７００〜１０００℃の温度により焼成処理をする。焼成時間は、上記温度域に少なくとも２時間、好ましくは５〜１５時間の範囲に設定する。焼成処理後、上記絶対湿度条件を保ったまま焼成物を冷却し、かるく解す程度に粉砕し、コバルト酸リチウムを得ればよい。また、前記処理操作は、これを再度繰り返して行うことが、該コバルト酸リチウムの水分安定性が更に向上する点からも好ましい。再度繰り返すときの焼成温度は、始めの焼成温度より低くてよく、３００〜１１００°Ｃ、好ましくは４００〜７００°Ｃの範囲である。焼成時間は１時間以上、好ましくは２〜１０時間の範囲に設定すればよい。前記絶対湿度とは、重量基準の湿度を意味し、乾燥空気１kg中に伴われる水蒸気の重量（ｇ／kg（乾燥空気））をいう。
【００２５】
また、本発明において、リチウムイオン二次電池用正極活物質としてのコバルト酸リチウムは、その優れた電子特性のゆえに、それを主成分として含有する正極板を製作した場合、優れた特性を有するリチウムイオン二次電池を提供することができる。二次電池は、例えばコバルト酸リチウムを主成分として、黒鉛粉末、ポリフッ化ビニリデンなどを混合加工して正極材とし、これを有機溶媒に分散させて混練ペーストを調製する。該混練ペーストをアルミ箔などの導伝性基板に塗布した後、乾燥し、加圧して適宜の形状に切断して正極板を得る。この正極板を用いて、リチウムイオン二次電池を構成する各部材を積層してリチウムイオン二次電池を作製する。
【００２６】
該二次電池は、例えばポータブル電子機器の電源、各種メモリーやソーラーバッテリーのバックアップ電源、電気自動車、電力貯蔵用バッテリーなどの広い用途に使用できる。
【００２７】
【発明の効果】
本発明によれば、常に安定した性能を発揮するエネルギー密度の高いコバルト酸リチウム系正極活物質を得ることができる。また、これを含有する正極材を用いたリチウムイオン二次電池は、優れた放電容量及びリサイクル特性を示す。
【００２８】
【実施例】
次に、実施例を挙げて、本発明をさらに具体的に説明するが、これは単に例示であって本発明を制限するものではない。
実施例１
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度５ｇ／kg' の空気を吹き込みながら昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００２９】
実施例２
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製しないで昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度５ｇ／kg' 条件の空気を吹き込みながら冷却、粉砕しコバルト酸リチウムを得た。
【００３０】
実施例３
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度１０ｇ／kg' の空気を吹き込みながら昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００３１】
実施例４
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製しないで昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度１０ｇ／kg' 条件の空気を吹き込みながら冷却、粉砕しコバルト酸リチウムを得た。
【００３２】
実施例５
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度２０ｇ／kg' の空気を吹き込みながら昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００３３】
実施例６
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製しないで昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度２０ｇ／kg' 条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００３４】
実施例７
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度１４ｇ／kg' の空気を吹き込みながら昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００３５】
実施例８
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製しないで昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度１４ｇ／kg' 条件の空気を吹き込みながら冷却、粉砕しコバルト酸リチウムを得た。
【００３６】
比較例１
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度２５ｇ／kg' の空気を吹き込みながら昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００３７】
比較例２
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、各混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製しないで昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度２５ｇ／kg' 条件の空気を吹き込みながら冷却、粉砕しコバルト酸リチウムを得た。
【００３８】
これら正極活物質のカールフィッシャー法による水分測定結果、コバルト平均酸化数の測定結果及び該正極活物質を用いて作製したリチウムイオン二次電池の電池性能結果を表１に示す。各測定方法及びリチウムイオン二次電池の作成方法を下記に示す。
【００３９】
（カールフィッシャー法による水分測定法）
（イ）法； 固体中の水分を測定するため水分気化装置（ＡＤＰ−３５１；京都電子工業社製）をＫＦ水分計と組み合わせて用いる。まず、１試料につき、２つのサンプルを準備し、このうち、１つは室温放置とし、該室温下にある試料を上記水分気化装置に導入し、１２０℃の加熱下、気化水分をＫＦ法により求め、この水分量を（Ａ）とする。また、他方の１つは、３０℃、相対湿度６０％の条件で１２時間放置し、放置後の試料を上記水分気化装置に導入し、１２０℃の加熱下、気化水分をＫＦ水分計により求め、これを（Ｂ）とする。
【００４０】
（ロ）法； 高温用の水分気化装置（ＡＤＰ−３５１；京都電子工業社製）をＫＦ水分計と組み合わせて用いる。始めに、室温放置下にある試料を上記水分気化装置に導入し、１２０℃の加熱下、気化水分をＫＦ法により求め、この水分量を（Ａ）とする。更に、該試料を２５０℃の温度まで加熱し、この温度で気化する水分をＫＦ水分計により求め、この水分量を（Ｃ）とする。
【００４１】
（ハ）法； 高温用の水分気化装置（ＡＤＰ−３５１；京都電子工業社製）をＫＦ水分計と組み合わせて用いる。１２０°Ｃで２時間乾燥下にある試料を上記水分気化装置に導入し、２５０℃の加熱下、気化水分をＫＦ法により求め、この水分量を（Ｄ）とする。
【００４２】
（ニ）法； 高温用の水分気化装置（ＡＤＰ−３５１；京都電子工業社製）をＫＦ水分計と組み合わせて用いる。１２０°Ｃで２時間乾燥後、２５０°Ｃで２時間加熱し、冷却した後、次いで該試料を３０°Ｃ、相対湿度６０％、１２時間放置後、さらに１２０°Ｃで２時間乾燥下にある試料を上記水分気化装置に導入し、２５０℃の加熱下、気化水分をＫＦ法により求め、この水分量を（Ｅ）とする。
【００４３】
（コバルト酸化数の測定）
・硫酸アンモニウム鉄溶液の標定
まず、硫酸アンモニウム鉄溶液（Fe(NH4)2SO4 ・8H2o）を１５ml分取し、０．１Ｎ−ＫＭｎＯ4 で滴定し、硫酸アンモニウム鉄の濃度（Ｎ）を求める。
・酸化数の測定
得られたコバルト酸リチウムを０．１ｇ（試料量）精秤し、１００mlビーカに入れ上記の標定された硫酸アンモニウム鉄溶液を２０ml加える。次いで濃硫酸を５ml加える。かき混ぜながら１０分間ゆっくり加温して溶解する。次に純水を約５０mlを加え、水浴中で室温まで冷却する。冷却後、すぐに０．１Ｎ−ＫＭｎＯ4 で電位差滴定を行う。
・全コバルト量の測定
得られたコバルト酸リチウム０．２ｇを硫酸に溶解し、１００mlに定溶する。その溶液を０．０１Ｎ−ＥＤＴＡで滴定し、全コバルト量（％）を求める。
【００４４】
上記測定結果を次式（１）及び（２）に代入し、（３）式よりコバルト平均酸化数を求める。
【００４５】
（リチウムイオン二次電池の作製）
上記により製造した各コバルト酸リチウム８５重量部、黒鉛粉末１０重量部及びポリフッ化ビニリデン５重量部を混合して正極材とし、これを２−メチルピロリドンに分散させて混練ペーストを調製した。該混練ペーストをアルミ箔に塗布したのち乾燥し、２ｔ／cm2 の圧力によりプレスして２cm角に打ち抜いて正極板を得た。この正極板を用い、各部材を積層してリチウムイオン二次電池を作製した。
【００４７】
（電池性能の評価）
作製したリチウムイオン二次電池を作動させ、初期容量及びサイクル特性を測定して電池性能を評価した。その結果を表１に示した。なお、サイクル特性は、正極に対して１mA/cm2で４．２Ｖまで充填したのち２．７Ｖまで放電させる充放電を２０サイクル繰り返し、次式（４）により算出した。
【００４８】
容量保持率＝
（２０サイクル目の放電容量）×１００／（１サイクル目の放電容量） (4)
【００４９】
【表１】
実施例９〜１０
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度１８ｇ／kg' の空気を吹き込みながら昇温し、９００℃（実施例９）及び９５０℃（実施例１０）になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００５１】
実施例１１
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製しないで昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度１８ｇ／kg' 条件を保ったまま冷却、粉砕しコバルト酸リチウムを得た。
【００５２】
これら正極活物質のカールフィッシャー滴定法（（ハ）法）による水分測定結果、コバルト平均酸化数の測定結果及び該正極活物質を用いて作製したリチウムイオン二次電池の電池性能結果を表２に示す。各測定方法及びリチウムイオン二次電池の作成方法は前記と同様である。
【００５３】
【表２】
実施例１２
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度１６ｇ／kg' の空気を吹き込みながら昇温し、９００℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕を行った。次いで、該粉末を再度、電気加熱炉に入れ、絶対湿度１６ｇ／kg' の空気を吹き込みながら昇温し、５００℃になった時点でこの温度に２時間保持して焼成した。得られた焼成物を絶対湿度１６ｇ／kg' 条件を保ったまま冷却、粉砕し、コバルト酸リチウムを得た。
【００５５】
実施例１３
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、該混合物をアルミナ坩堝に充填して電気加熱炉に入れ、絶対湿度１６ｇ／kg' の空気を吹き込みながら昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を上記絶対湿度条件を保ったまま冷却、粉砕を行った。次いで、該粉末を再度、電気加熱炉に入れ、絶対湿度１６ｇ／kg' の空気を吹き込みながら昇温し、６００℃になった時点でこの温度に２時間保持して焼成した。得られた焼成物を絶対湿度１６ｇ／kg' 条件を保ったまま冷却、粉砕し、コバルト酸リチウムを得た。
【００５６】
実施例１４
炭酸リチウム粉末と酸化コバルトをＬｉ／Ｃｏ原子比が１となるように秤量し、乳鉢で十分混合して均一な混合物を調製した。次いで、各混合物をアルミナ坩堝に充填して電気加熱炉に入れ、特に湿度調製をしないで昇温し、９５０℃になった時点でこの温度に１０時間保持して焼成した。得られた焼成物を絶対湿度１８ｇ／kg' 条件を保ったまま冷却、粉砕を行った。次いで、該粉末を再度、電気加熱炉に入れ、特に湿度調製をしないで昇温し、５００℃になった時点でこの温度に２時間保持して焼成した。得られた焼成物を絶対湿度１６ｇ／kg' 条件を保ったまま冷却、粉砕し、コバルト酸リチウムを得た。
【００５７】
これら正極活物質のカールフィッシャー滴定法（（ニ）法）による水分測定結果、コバルト平均酸化数の測定結果及び該正極活物質を用いて作製したリチウムイオン二次電池の電池性能結果を表３に示す。各測定方法及びリチウムイオン二次電池の作成方法は前記と同様である。
【００５８】
【表３】
表１〜表３より、実施例品のコバルト酸リチウムを正極剤としてリチウムイオン二次電池を作製すれば、初期容量が大きく、優れたサイクル特性を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lithium cobalt oxide-based positive electrode active material for a lithium ion secondary battery, a production method thereof, and a lithium ion secondary battery using a positive electrode material containing the same.
[0002]
[Technology technology]
In recent years, as home appliances have become portable and cordless, lithium ion secondary batteries have been put to practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. Regarding this lithium ion secondary battery, in 1980, Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium ion secondary batteries (“Material Research Bulletin” vo115, P783-789 (1980)). Since then, research and development on lithium cobaltate-based positive electrode active materials have been actively promoted, and many proposals have been made so far.
[0003]
Conventionally, as a technique for increasing the energy density of the positive electrode active material, for example, the composition of lithium cobaltate is LixCoO. 2 (However, 1.05 ≦ x ≦ 1.3) to make it rich in lithium (Japanese Patent Laid-Open No. 3-127454), conversely, LixCoO 2 (However, 0 <x ≦ 1), which is enriched by cobalt (Japanese Patent Laid-Open No. 3-134969), doped with metal ions such as Mn, W, Ni, La, Zr (Japanese Patent Laid-Open No. 201368, JP-A-4-328277, JP-A-4-319259, JP-A-4-319260, etc.), residual Li in cobalt oxide 2 CO Three The content of which is 10% by weight or less (JP-A-4-56064) has been proposed.
[0004]
On the other hand, as a technology requiring physical characteristics of the lithium cobaltate-based positive electrode active material, particularly specific surface area, LiCoO 2 Specific surface area of 2m 2 / g or less (JP-A-4-56064), the specific surface area of the lithium composite oxide is 0.01 to 3.0 m. 2 / g (Japanese Patent Laid-Open No. 4-249073), Li x Co y O 2 Specific surface area by BET method (0 <x ≦ 1.3, 1.8 ≦ y ≦ 2.2) is 0.5 to 10.0m 2 It has been proposed that by using lithium cobaltate having / g (Japanese Patent Laid-Open No. 6-103976) or the like, it is possible to improve the decrease in discharge capacity accompanying the progress of the discharge cycle.
[0005]
LiCoO 2 Made amorphous (Japanese Patent Laid-Open No. 5-21066), LiCoO 2 Giving a certain particle size characteristic (Japanese Patent Laid-Open Nos. 4-33260 and 5-94822), LiCoO 2 Are known in which crystal grains having a specific X-ray diffraction intensity are used (JP-A-3-272564, JP-A-5-36414). Further, regarding the production method of the lithium cobaltate based positive electrode active material, JP-A-3-285262, JP-A-4-49074, JP-A-4-123762, JP-A-5-54886, JP-A-5 Many proposals have been made in Japanese Patent No. -54888, Japanese Patent Laid-Open No. 5-62678, Japanese Patent Laid-Open No. 5-182667, and the like.
[0006]
[Problems to be solved by the invention]
However, lithium cobaltate used as a positive electrode active material of a lithium ion secondary battery is, for example, a lithium compound such as lithium carbonate and a cobalt compound such as cobalt oxide having an Li / Co atomic ratio of 0.9 to 1.2. It is produced by mixing in a range and firing the mixture under a temperature condition of 600 to 1100 ° C., but the physical properties of the obtained lithium cobaltate slightly change depending on the production conditions, and the discharge characteristics as a battery This significantly affects the performance of the positive electrode active material such as discharge cycle characteristics. As a result, it is difficult to say that conventional lithium ion secondary batteries using lithium cobalt oxide as the positive electrode active material exhibit stable and sufficient performance. It was a thing.
[0007]
Accordingly, an object of the present invention is to provide a lithium cobaltate-based positive electrode active material having a high energy density and a secondary battery exhibiting stable discharge capacity and cycle characteristics.
[0008]
[Means for Solving the Problems]
In such a situation, the present inventor has intensively studied, and as a result, the amount of water contained in lithium cobalt oxide suitable as a positive electrode active material for a lithium secondary battery is less than a specific value, and does not absorb moisture even in a high humidity state. In addition, the inventors have found that those in which the oxidation number of cobalt is controlled within a specific range are excellent in discharge capacity and discharge retention and give high energy density, and have completed the present invention.
That is, according to the present invention, in the lithium cobaltate positive electrode active material for a lithium ion secondary battery, the lithium cobaltate is allowed to stand at room temperature, and then the moisture measurement amount (A) by the 120 ° C. moisture vaporization method by Karl Fischer titration method is 150 ppm or less and / or the lithium cobaltate is allowed to stand for 12 hours at 30 ° C. and 60% relative humidity, and then the moisture content (B) measured by the Karl Fischer titration method at 120 ° C. is 200 ppm or less. The lithium cobaltate type positive electrode active material for a lithium ion secondary battery is provided.
[0009]
The present invention also relates to a lithium cobaltate-based positive electrode active material for a lithium ion secondary battery, wherein the lithium cobaltate is allowed to stand at room temperature, and then measured for water content (120) by a water vaporization method at 120 ° C. by Karl Fischer titration. Then, in the measured water content (C) at 250 ° C. moisture vaporization method, the (A + C) value is 300 ppm or less and the A value is 150 ppm or less. A positive electrode active material is provided.
[0010]
Further, the present invention relates to a lithium cobaltate positive electrode active material for a lithium ion secondary battery, wherein the lithium cobaltate is dried at 120 ° C. for 2 hours, and then measured for moisture by a 250 ° C. moisture vaporization method by Karl Fischer titration. The present invention provides a lithium cobaltate-based positive electrode active material for a lithium secondary battery, wherein the amount (D) is 100 ppm or less.
[0011]
Further, the present invention provides a lithium cobaltate positive electrode active material for a lithium ion secondary battery, wherein the lithium cobaltate is dried at 120 ° C. for 2 hours, then calcined at 250 ° C. for 2 hours, cooled, After the lithium cobaltate was left at 30 ° C., 60% relative humidity for 12 hours, and further dried at 120 ° C. for 2 hours, the water content (E) measured by the water vaporization method at 250 ° C. by Karl Fischer titration was 50 ppm or less. The present invention provides a lithium cobaltate positive electrode active material for a lithium secondary battery.
[0012]
The present invention also provides a lithium cobaltate positive electrode active material for lithium ion secondary batteries, wherein the cobalt oxidation number in lithium cobaltate is 2.90 to 3.10 by potentiometric titration.
[0013]
The present invention also relates to a method for producing lithium cobaltate by mixing lithium carbonate and cobalt oxide, followed by firing, cooling and pulverization, and at least in each of the cooling and pulverization treatment steps, an absolute humidity of 20 g / kg ′. The present invention provides a method for producing a lithium cobaltate-based positive electrode active material for a lithium ion secondary battery, wherein each treatment operation is performed while blowing the following air.
[0014]
The present invention also relates to a method for producing lithium cobaltate by mixing lithium carbonate and cobalt oxide, followed by firing, cooling and pulverization, and at least in each of the cooling and pulverization treatment steps, an absolute humidity of 20 g / kg ′. The present invention provides a method for producing a lithium cobaltate positive electrode active material for a lithium ion secondary battery, wherein each treatment operation is performed while blowing the following air, and the treatment operation is repeated again.
[0015]
The present invention also provides a lithium ion secondary battery characterized in that a positive electrode material containing the lithium cobaltate positive electrode active material for lithium ion secondary batteries is used.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the lithium cobaltate positive electrode active material for a lithium ion secondary battery of the present invention, the lithium cobaltate is allowed to stand at room temperature and then moisture at 120 ° C. by Karl Fischer titration (hereinafter sometimes simply referred to as “KF method”). The water content (A) measured by the vaporization method is 150 ppm or less, preferably 100 ppm or less. Further, after the lithium cobaltate is allowed to stand for 12 hours at 30 ° C. and a relative humidity of 60%, the measured water content (B) in the 120 ° C. moisture vaporization method by the KF method is 200 ppm or less, preferably 150 ppm or less. . Moreover, it is preferable that the difference (B−A) between the (A) value and the (B) value is 50 ppm or less. That is, it is important that the lithium cobalt oxide of the present invention is an extremely stable compound with respect to moisture, in which the amount of moisture contained in the lithium cobalt oxide is not more than a certain amount and is difficult to absorb moisture even in a particular humidity atmosphere. It will be a physical property. If the above (A) value exceeds a water content of 150 ppm and the (B) value exceeds 200 ppm is used as the positive electrode material, the electrolytic solution is decomposed and the secondary battery characteristics are deteriorated.
[0017]
The moisture measurement method of the 120 ° C. moisture vaporization method by the KF method is not particularly limited, and may be a known method. For example, a commercially available Karl Fischer moisture meter and a moisture vaporizer may be used in combination. That is, after setting the sample in the moisture vaporizer, the vaporized moisture generated under the heating condition of 120 ° C. is collected together with the dry nitrogen of the carrier gas, introduced into a Karl Fischer moisture meter, and the moisture content is measured. That's fine.
[0018]
Moreover, as room temperature standing conditions, it is left to stand on the conditions of about 20-25 degreeC temperature and 20-50% of relative humidity.
[0019]
In the present invention, the lithium cobaltate in the lithium cobaltate-based positive electrode active material for a lithium ion secondary battery is allowed to stand at room temperature, and then the moisture content (A) measured by the water vaporization method at 120 ° C. by the KF method is measured. (A + C) value is 300 ppm or less and A value is 150 ppm or less in the measured water content (C) in the 250 ° C. moisture vaporization method. The preferable range of (A + C) value is 150 ppm or less, and the preferable range of A value is 100 ppm or less.
[0020]
Further, in the present invention, after the lithium cobaltate in the lithium cobaltate-based positive electrode active material for a lithium ion secondary battery is dried at 120 ° C. for 2 hours, the amount of moisture measured by a 250 ° C. moisture vaporization method by Karl Fischer titration method (D) is 100 ppm or less. (D) The preferable range of a value is 50 ppm or less.
[0021]
In the present invention, in the lithium cobaltate-based positive electrode active material for a lithium ion secondary battery, the lithium cobaltate is dried at 120 ° C. for 2 hours, then calcined at 250 ° C. for 2 hours, cooled, After the lithium cobaltate was left at 30 ° C., 60% relative humidity for 12 hours, and further dried at 120 ° C. for 2 hours, the water content (E) measured by the water vaporization method at 250 ° C. by Karl Fischer titration was 50 ppm or less. It is.
[0022]
The measurement method by the 250 ° C. moisture vaporization method by the KF method may be performed in the same manner as the measurement method by the 120 ° C. moisture vaporization method by the KF method, except that 120 ° C. is changed to 250 ° C. The mechanism of the distilled water due to the difference in heating temperature between 120 ° C. and 250 ° C. is not clear, but under 120 ° C. heating conditions, the water physically adsorbed on the particle surface distills, When the temperature is raised to 250 ° C., it is considered that the moisture chemically adsorbed in the fine pores resulting from the crystal structure of the particles distills. When using particles that exceed the above values for the positive electrode active material of a lithium ion secondary battery, not only the water adhering to the surface, but also the water gradually distills from the crystal particles after a long cycle, This results in deterioration of battery characteristics such as initial capacity and cycle characteristics, which is not preferable. That is, it is preferable that not only the water on the particle surface but also the water adsorbed in the crystal particles is very little, and that the use of such a compound as a positive electrode active material for a lithium ion secondary battery has excellent battery characteristics. it can.
[0023]
The lithium cobaltate positive electrode active material of the present invention has a cobalt oxidation number in lithium cobaltate of 2.90 to 3.10, preferably 2.95 to 3.05 as measured by potentiometric titration. Those are preferred. Usually lithium cobaltate (LiCoO 2 ) Although the oxidation number of cobalt in the composition formula is theoretically trivalent, the oxidation number of cobalt in the compound does not always become a theoretical value depending on the production method, and deviates greatly from the theoretical valence. Sometimes. By changing the oxidation number of cobalt, the crystal structure is distorted. If this is used as a positive electrode material for a lithium ion secondary battery and charging and discharging are repeated, battery characteristics such as cycle characteristics deteriorate, which is not preferable.
[0024]
In the present invention, the method for producing a cobalt lithium-based positive electrode active material for a lithium ion secondary battery is a method in which lithium carbonate and cobalt oxide are mixed and then calcined, cooled, and pulverized. In each processing step, preferably in each of the baking, cooling, and pulverization processing steps, each processing operation may be performed while blowing air having an absolute humidity of 20 g / kg ′ or less. For example, lithium carbonate and cobalt oxide are mixed at a blending ratio in the range of about 1 as an atomic ratio of Li / Co, preferably 0.99 to 1.10. Next, the mixture is fired at a temperature of 600 ° C. to 1100 ° C., preferably 700 to 1000 ° C. while blowing air having an absolute humidity of 20 g / kg ′ or less. The firing time is set in the above temperature range for at least 2 hours, preferably in the range of 5 to 15 hours. After the firing treatment, the fired product is cooled while maintaining the above absolute humidity condition, and pulverized to such an extent that it can be easily broken to obtain lithium cobalt oxide. Further, it is preferable that the treatment operation is repeated again from the viewpoint of further improving the moisture stability of the lithium cobalt oxide. The firing temperature when it is repeated again may be lower than the initial firing temperature, and is in the range of 300 to 1100 ° C, preferably 400 to 700 ° C. The firing time may be set to 1 hour or longer, preferably 2 to 10 hours. The absolute humidity means humidity based on weight, and means the weight of water vapor (g / kg (dry air)) in 1 kg of dry air.
[0025]
In the present invention, lithium cobaltate as a positive electrode active material for a lithium ion secondary battery has excellent characteristics when a positive electrode plate containing it as a main component is produced because of its excellent electronic characteristics. An ion secondary battery can be provided. In the secondary battery, for example, lithium cobalt oxide as a main component, graphite powder, polyvinylidene fluoride, and the like are mixed and processed into a positive electrode material, which is dispersed in an organic solvent to prepare a kneaded paste. The kneaded paste is applied to a conductive substrate such as an aluminum foil, dried, pressed and cut into an appropriate shape to obtain a positive electrode plate. Using this positive electrode plate, each member constituting the lithium ion secondary battery is laminated to produce a lithium ion secondary battery.
[0026]
The secondary battery can be used in a wide range of applications such as a power source for portable electronic devices, a backup power source for various memories and solar batteries, an electric vehicle, and a battery for storing power.
[0027]
【The invention's effect】
According to the present invention, it is possible to obtain a lithium cobaltate positive electrode active material with high energy density that always exhibits stable performance. Moreover, the lithium ion secondary battery using the positive electrode material containing this shows the outstanding discharge capacity and recycling characteristics.
[0028]
【Example】
EXAMPLES Next, the present invention will be described more specifically with reference to examples, but this is merely an example and does not limit the present invention.
Example 1
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible, placed in an electric heating furnace, heated while blowing air having an absolute humidity of 5 g / kg ′, and when the temperature reached 900 ° C., this temperature was maintained for 10 hours to be fired. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition to obtain lithium cobalt oxide.
[0029]
Example 2
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised without particularly adjusting the humidity, and when the temperature reached 900 ° C., the temperature was maintained at this temperature for 10 hours and fired. The obtained fired product was cooled and pulverized while blowing air having an absolute humidity of 5 g / kg 'to obtain lithium cobalt oxide.
[0030]
Example 3
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised while blowing air having an absolute humidity of 10 g / kg ′, and when the temperature reached 900 ° C., this temperature was maintained for 10 hours to be fired. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition to obtain lithium cobalt oxide.
[0031]
Example 4
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised without particularly adjusting the humidity, and when the temperature reached 900 ° C., the temperature was maintained at this temperature for 10 hours and fired. The obtained fired product was cooled and pulverized while blowing air having an absolute humidity of 10 g / kg 'to obtain lithium cobalt oxide.
[0032]
Example 5
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised while blowing air having an absolute humidity of 20 g / kg ′, and when the temperature reached 900 ° C., this temperature was maintained for 10 hours for firing. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition to obtain lithium cobalt oxide.
[0033]
Example 6
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised without particularly adjusting the humidity, and when the temperature reached 900 ° C., the temperature was maintained at this temperature for 10 hours and fired. The obtained fired product was cooled and pulverized while maintaining the absolute humidity of 20 g / kg 'to obtain lithium cobalt oxide.
[0034]
Example 7
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Subsequently, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised while blowing air having an absolute humidity of 14 g / kg ', and when the temperature reached 950 ° C., this temperature was maintained for 10 hours for firing. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition to obtain lithium cobalt oxide.
[0035]
Example 8
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised without particularly adjusting the humidity, and when the temperature reached 950 ° C., the temperature was maintained at this temperature for 10 hours for firing. The obtained fired product was cooled and pulverized while blowing air having an absolute humidity of 14 g / kg 'to obtain lithium cobalt oxide.
[0036]
Comparative Example 1
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised while blowing air having an absolute humidity of 25 g / kg ′, and when the temperature reached 950 ° C., this temperature was maintained for 10 hours for firing. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition to obtain lithium cobalt oxide.
[0037]
Comparative Example 2
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, each mixture was filled in an alumina crucible and placed in an electric heating furnace, and the temperature was raised without particularly adjusting the humidity. The obtained fired product was cooled and pulverized while blowing air having an absolute humidity of 25 g / kg 'to obtain lithium cobalt oxide.
[0038]
Table 1 shows the moisture measurement results of these positive electrode active materials by the Karl Fischer method, the measurement results of the average cobalt oxidation number, and the battery performance results of the lithium ion secondary batteries produced using the positive electrode active materials. Each measuring method and the production method of a lithium ion secondary battery are shown below.
[0039]
(Moisture measurement method by Karl Fischer method)
(A) Method; A moisture vaporizer (ADP-351; manufactured by Kyoto Electronics Industry Co., Ltd.) is used in combination with a KF moisture meter to measure moisture in a solid. First, two samples are prepared for each sample, one of which is allowed to stand at room temperature, the sample at room temperature is introduced into the moisture vaporizer, and the vaporized moisture is heated by 120 ° C. by the KF method. The water content is determined as (A). The other one is allowed to stand for 12 hours under the conditions of 30 ° C. and 60% relative humidity, and the sample after the standing is introduced into the moisture vaporizer, and the vaporized moisture is obtained with a KF moisture meter under heating at 120 ° C. This is defined as (B).
[0040]
(B) Method: A high temperature moisture vaporizer (ADP-351; manufactured by Kyoto Electronics Industry Co., Ltd.) is used in combination with a KF moisture meter. First, a sample left at room temperature is introduced into the moisture vaporizer, and the vaporized moisture is determined by the KF method under heating at 120 ° C., and this moisture content is defined as (A). Further, the sample is heated to a temperature of 250 ° C., the water vaporized at this temperature is obtained with a KF moisture meter, and this moisture content is defined as (C).
[0041]
(C) Method: A high-temperature moisture vaporizer (ADP-351; manufactured by Kyoto Electronics Industry Co., Ltd.) is used in combination with a KF moisture meter. A sample that has been dried at 120 ° C. for 2 hours is introduced into the moisture vaporizer, and the vaporized moisture is determined by KF method while heating at 250 ° C., and this moisture content is defined as (D).
[0042]
(D) Method: A high-temperature moisture vaporizer (ADP-351; manufactured by Kyoto Electronics Industry Co., Ltd.) is used in combination with a KF moisture meter. After drying at 120 ° C. for 2 hours, heating at 250 ° C. for 2 hours and cooling, the sample is then allowed to stand for 12 hours at 30 ° C. and a relative humidity of 60%, and further dried at 120 ° C. for 2 hours. A sample is introduced into the moisture vaporizer, and vaporized moisture is determined by KF method under heating at 250 ° C., and this moisture content is defined as (E).
[0043]
(Measurement of cobalt oxidation number)
・ Standardization of ammonium iron sulfate solution
First, ammonium iron sulfate solution (Fe (NH Four ) 2 SO Four ・ 8H 2 o) 15 ml was taken and 0.1N-KMnO Four To determine the concentration (N) of ammonium iron sulfate.
・ Measurement of oxidation number
0.1 g (sample amount) of the obtained lithium cobaltate is precisely weighed, put into a 100 ml beaker, and 20 ml of the above-mentioned standardized ammonium iron sulfate solution is added. Then 5 ml of concentrated sulfuric acid is added. Dissolve by gently warming for 10 minutes while stirring. Next, about 50 ml of pure water is added and cooled to room temperature in a water bath. Immediately after cooling, 0.1N-KMnO Four Perform potentiometric titration with.
・ Measurement of total cobalt content
0.2 g of the obtained lithium cobaltate is dissolved in sulfuric acid and dissolved in 100 ml. The solution is titrated with 0.01N-EDTA to determine the total cobalt content (%).
[0044]
The above measurement results are substituted into the following formulas (1) and (2), and the average cobalt oxidation number is obtained from the formula (3).
[0045]
(Production of lithium ion secondary battery)
85 parts by weight of each lithium cobaltate produced above, 10 parts by weight of graphite powder and 5 parts by weight of polyvinylidene fluoride were mixed to prepare a positive electrode material, which was dispersed in 2-methylpyrrolidone to prepare a kneaded paste. The kneaded paste is applied to an aluminum foil and then dried, 2 t / cm 2 A positive electrode plate was obtained by pressing with a pressure of 2 mm and punching into a 2 cm square. Using this positive electrode plate, each member was laminated to produce a lithium ion secondary battery.
[0047]
(Evaluation of battery performance)
The fabricated lithium ion secondary battery was operated, and the initial capacity and cycle characteristics were measured to evaluate the battery performance. The results are shown in Table 1. The cycle characteristics are 1mA / cm with respect to the positive electrode. 2 After charging to 4.2V, charging / discharging to discharge to 2.7V was repeated 20 cycles, and calculation was performed according to the following formula (4).
[0048]
Capacity retention =
(Discharge capacity at 20th cycle) × 100 / (Discharge capacity at 1st cycle) (4)
[0049]
[Table 1]
Examples 9-10
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace, and the temperature was raised while blowing air having an absolute humidity of 18 g / kg ', and the temperature reached 900 ° C. (Example 9) and 950 ° C. (Example 10). At this point, this temperature was maintained for 10 hours and fired. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition to obtain lithium cobalt oxide.
[0051]
Example 11
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised without particularly adjusting the humidity, and when the temperature reached 950 ° C., the temperature was maintained at this temperature for 10 hours for firing. The obtained fired product was cooled and ground while maintaining the absolute humidity of 18 g / kg 'to obtain lithium cobalt oxide.
[0052]
Table 2 shows the moisture measurement results of these positive electrode active materials by Karl Fischer titration method ((c) method), the measurement results of the average cobalt oxidation number, and the battery performance results of lithium ion secondary batteries produced using the positive electrode active materials. Show. Each measuring method and the production method of a lithium ion secondary battery are the same as the above.
[0053]
[Table 2]
Example 12
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised while blowing air with an absolute humidity of 16 g / kg ', and when the temperature reached 900 ° C., this temperature was maintained for 10 hours for firing. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition. Next, the powder was again put into an electric heating furnace, heated while blowing air having an absolute humidity of 16 g / kg ', and when the temperature reached 500 ° C., this temperature was maintained for 2 hours and baked. The obtained fired product was cooled and pulverized while maintaining the absolute humidity of 16 g / kg 'to obtain lithium cobalt oxide.
[0055]
Example 13
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, the mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised while blowing air with an absolute humidity of 16 g / kg ′, and when the temperature reached 950 ° C., this temperature was maintained for 10 hours to be fired. The obtained fired product was cooled and pulverized while maintaining the above absolute humidity condition. Next, the powder was again put into an electric heating furnace, heated while blowing air having an absolute humidity of 16 g / kg ', and when the temperature reached 600 ° C., this temperature was maintained for 2 hours and fired. The obtained fired product was cooled and pulverized while maintaining the absolute humidity of 16 g / kg 'to obtain lithium cobalt oxide.
[0056]
Example 14
Lithium carbonate powder and cobalt oxide were weighed so that the Li / Co atomic ratio was 1, and thoroughly mixed in a mortar to prepare a uniform mixture. Next, each mixture was filled in an alumina crucible and placed in an electric heating furnace. The temperature was raised without particularly adjusting the humidity, and when the temperature reached 950 ° C., this temperature was maintained for 10 hours to be fired. The obtained fired product was cooled and pulverized while maintaining the absolute humidity of 18 g / kg ′. Next, the powder was again put in an electric heating furnace, and the temperature was raised without particularly adjusting the humidity. When the temperature reached 500 ° C., the powder was held at this temperature for 2 hours and fired. The obtained fired product was cooled and pulverized while maintaining the absolute humidity of 16 g / kg 'to obtain lithium cobalt oxide.
[0057]
Table 3 shows the moisture measurement results of these positive electrode active materials by Karl Fischer titration method ((d) method), the measurement results of the average oxidation number of cobalt, and the battery performance results of lithium ion secondary batteries produced using the positive electrode active materials. Show. Each measuring method and the production method of a lithium ion secondary battery are the same as the above.
[0058]
[Table 3]
From Tables 1 to 3, if a lithium ion secondary battery is prepared using the lithium cobaltate of the example product as a positive electrode agent, the initial capacity is large and excellent cycle characteristics are exhibited.
Claims (9)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP20849297A JP3706718B2 (en) | 1997-04-01 | 1997-07-17 | Lithium ion secondary battery positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery |
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| JP9-98297 | 1997-04-01 | ||
| JP9829797 | 1997-04-01 | ||
| JP20849297A JP3706718B2 (en) | 1997-04-01 | 1997-07-17 | Lithium ion secondary battery positive electrode active material for lithium ion secondary battery, method for producing the same, and lithium ion secondary battery |
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| JP3706718B2 true JP3706718B2 (en) | 2005-10-19 |
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| JP4106644B2 (en) * | 2000-04-04 | 2008-06-25 | ソニー株式会社 | Battery and manufacturing method thereof |
| JP2005206422A (en) * | 2004-01-22 | 2005-08-04 | Honjo Chemical Corp | High density lithium cobaltate and its producing method |
| WO2011077932A1 (en) | 2009-12-22 | 2011-06-30 | Jx日鉱日石金属株式会社 | Positive electrode active material for a lithium-ion battery, positive electrode for a lithium-ion battery, lithium-ion battery using same, and precursor to a positive electrode active material for a lithium-ion battery |
| CN105514420A (en) | 2010-12-03 | 2016-04-20 | Jx日矿日石金属株式会社 | Positive electrode active material for lithium-ion battery, positive electrode for lithium-ion battery, and lithium-ion battery |
| WO2012098724A1 (en) | 2011-01-21 | 2012-07-26 | Jx日鉱日石金属株式会社 | Method for producing positive-electrode active material for lithium-ion battery and positive-electrode active material for lithium-ion battery |
| JP6292738B2 (en) * | 2012-01-26 | 2018-03-14 | Ｊｘ金属株式会社 | Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery |
| JP6292739B2 (en) * | 2012-01-26 | 2018-03-14 | Ｊｘ金属株式会社 | Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery, and lithium ion battery |
| WO2014051148A1 (en) | 2012-09-28 | 2014-04-03 | Jx日鉱日石金属株式会社 | Positive-electrode active substance for lithium-ion cell, positive electrode for lithium-ion cell, and lithium-ion cell |
| US10746711B2 (en) | 2015-06-12 | 2020-08-18 | Envision Aesc Energy Devices Ltd. | Method of measuring quantity of moisture in electrode, method of manufacturing electrode for lithium-ion secondary battery, moisture quantity measuring apparatus, and method of measuring moisture quantity |
| JP7167488B2 (en) * | 2018-05-29 | 2022-11-09 | トヨタ自動車株式会社 | Positive electrode, all-solid battery and manufacturing method thereof |
| JP7006508B2 (en) * | 2018-05-29 | 2022-01-24 | トヨタ自動車株式会社 | Positive electrode, all-solid-state battery and manufacturing method thereof |
| JP7135526B2 (en) * | 2018-07-18 | 2022-09-13 | トヨタ自動車株式会社 | Method for producing electrode layer for all-solid-state battery |
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