JP4965019B2 - Cathode active material for non-aqueous electrolyte secondary battery, production method thereof, and non-aqueous electrolyte secondary battery - Google Patents
Cathode active material for non-aqueous electrolyte secondary battery, production method thereof, and non-aqueous electrolyte secondary battery Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、非水溶液を電解質とした二次電池における、負荷特性を有効に改善し、高容量化が可能な非水電解液２次電池用活物質、その製造方法及びそれを用いた非水電解液２次電池に関する。
【０００２】
【従来の技術】
近年、ビデオカメラ、携帯型ＣＤ、携帯電話、ＰＤＡやノートパソコン等の携帯用電子機器の小型化、軽量化、高性能化が進んでいる。これらの携帯用電子機器の電源には、高容量かつ重負荷特性の優れた安全性の高い二次電池が必要とされている。このような目的に合致した二次電池としてシール鉛蓄電池やニッケル・カドミウム蓄電池が使用されてきたが、よりエネルギー密度の高い電池としてニッケル水素蓄電池や非水電解液二次電池としてリチウムイオン二次電池が実用化に至っている。
リチウムイオン二次電池は、正極活物質として、リチウムと、コバルト、ニッケル、マンガン等の遷移金属との複合酸化物を用い、負極活物質にリチウムイオンを挿入・脱挿入できる炭素等の炭素質材料を用いた二次電池であり、ニッケル水素蓄電池等に比ベて容量が大きく、また電圧が高いという特徴を持っている。
【０００３】
【発明が解決しようとする課題】
リチウムイオン二次電池は、上記のような長所を持つ反面、Ｎｉ／ＭＨ電池やＮｉ／Ｃｄ電池に比べ高負荷特性が劣るという欠点を持っている。その特性改善のために正極活物質中の導電剤を増加、正極活物質を構成する元素として他の元素、例えばＡｌ等の添加、正極活物質の微粒化等が検討されているが、いずれの場合も電池容量の低下を招く。
【０００４】
従って、本発明の目的は、非水電解液２次電池における負荷特性を有効に改善し、高容量化が可能な非水電解液２次電池用正極活物質及びその製造方法を提供することにある。
本発明の別の目的は、優れた放電容量が得られる非水電解液２次電池を提供することにある。
【０００５】
【課題を解決するための手段】
本発明によれば、リチウムを含有し、且つＣｏ、Ｎｉ及びＦｅからなる群より選択される少なくとも１種の遷移元素を含む酸化物(Ｘ)又はそれらの複合酸化物と、ＬｉＬｎＯ2(式中、ＬｎはYbを示す。)で表される酸化物(Ｙ)とを含む粒子状焼結物であり、該焼結物中の酸化物（Ｙ）の含有割合が０．５〜３質量％であることを特徴とする非水電解液２次電池用正極活物質が提供される。
また本発明によれば、リチウムを含有し、且つＣｏ、Ｎｉ及びＦｅからなる群より選択される少なくとも１種の遷移元素を含む酸化物(Ｘ)又はそれらの複合酸化物と、ＬｉＬｎＯ2(式中、ＬｎはYbを示す。)で表される酸化物(Ｙ)とを、バインダーと共に造粒又は成形する工程(Ａ)と、
工程(Ａ)で得られた造粒物又は成形体を、該造粒物又は成形体中に含まれるＬｉ化合物の少なくとも一部が溶融する温度であって、且つ６００〜８００℃の温度で保持する工程(Ｂ)と、
工程(Ｂ)の後、該工程(Ｂ)における保持温度より高く、且つ８００〜１１００℃の温度で保持する工程(Ｃ)とを含むことを特徴とする上記非水電解液２次電池用正極活物質の製造方法が提供される。
更に本発明によれば、正極活物質粉末を有する正極と、負極と、電解液とを備え、該正極活物質粉末が、上記非水電解液２次電池用正極活物質であることを特徴とする非水電解液２次電池が提供される。
【０００６】
【発明の実施の形態】
以下、本発明を更に詳細に説明する。
本発明の非水電解液２次電池用正極活物質(以下、本発明の正極活物質という)は、リチウムを含有し、且つＣｏ、Ｎｉ及びＦｅからなる群より選択される少なくとも１種の遷移元素を含む酸化物(Ｘ)又はそれらの複合酸化物と、ＬｉＬｎＯ2(式中、ＬｎはYbを示す。)で表される酸化物(Ｙ)とを含む粒子状焼結物である。
【０００７】
本発明の正極活物質において前記酸化物(Ｙ)は、酸化物(Ｘ)におけるリチウム(Ｌｉ)の出し入れを円滑に行わせる働きを有し、負荷特性向上及び放電容量向上に寄与するものと考えられる。即ち、充電反応時において、酸化物(Ｘ)中のＬｉが酸化物(Ｙ)を介してＬｉ+に、また放電反応時には電解液中のＬｉ+が酸化物(Ｙ)上で還元され、酸化物(Ｘ)中へと拡散していくために負荷特性の向上及び高放電容量化が可能になるものと思われる。更に、酸化物(Ｙ)が酸化物(Ｘ)の粒子表面に分散して存在した形態の粒子や、酸化物(Ｘ)と酸化物(Ｙ)との複合体粒子を存在させることにより、非水電解液との親和性が向上し、負荷特性の向上及び高放電容量化が可能になるものと思われる。
【０００８】
本発明の正極活物質において、前記酸化物(Ｘ)及び酸化物(Ｙ)は、各粒子の混合物の形態、各一次粒子が二次粒子となった形態等を含む。またこれらの形態の粒子に加えて、酸化物(Ｘ)及び酸化物(Ｙ)の複合体粒子を含んでいても良い。
前記各粒子の混合物の形態としては、酸化物(Ｙ)が、酸化物(Ｘ)の粒子表面に分散して存在した形態であることが所望の効果をより向上させるために好ましい。特に、酸化物(Ｙ)が酸化物(Ｘ)の表面に化学結合している形態が好ましい。
【０００９】
前記酸化物(Ｘ)又はそれらの複合酸化物としては、例えば、ＬｉＣｏＯ2、ＬｉＮｉＯ 2 、ＬｉＦｅＯ2や、ＬｉＣｏ0.8Ｎｉ0.2Ｏ2、ＬｉＮｉ0.5Ｃｏ0.5Ｏ2、ＬｉＮｉ0.9Ｃｏ0.1Ｏ2等のＬｉＣｏXＮｉ(1-X)Ｏ2(０≦Ｘ≦１)で表される酸化物等が挙げられる。
【００１０】
酸化物(Ｙ)は、ＬｉＹｂＯ 2 である。
【００１１】
本発明において、酸化物(Ｘ)及び酸化物(Ｙ)の合計量に対する酸化物(Ｙ)の含有割合は、非水電解液２次電池とした際の放電容量を良好にするために、０．５〜３質量％である。０．０１質量％未満では所望の効果が得られないので好ましくない。また、２０質量％を超える場合は活物質の利用率の向上よりも活物質の減少による容量低下が生じる恐れがある。この際、本発明の正極活物質が酸化物(Ｘ)と酸化物(Ｙ)との複合酸化物を含む場合には、該複合酸化物中における酸化物(Ｙ)に相当する割合を酸化物(Ｙ)の含有割合に含めることにする。
【００１２】
本発明の正極活物質において、前記酸化物(Ｘ)、酸化物(Ｙ)及び複合体粒子の粒径は、その１次粒子の９０％以上の粒子径が１μｍ以下、特に０．１〜０．５μｍであり、かつ該１次粒子の集合体である２次粒子の平均粒径が５〜１５μｍの範囲であることが好ましい。特に、酸化物(Ｙ)の粒子径は、放電容量を大きくするためにその平均粒径が１μｍ以下とすることが好ましい。酸化物(Ｙ)の粒子径が大きくなるにつれその添加効果は減少する。即ち、酸化物(Ｙ)中のＬｉの拡散が問題になり、添加効果が低下するものと考えられる。１次粒子の粒子径が０．１μｍ未満では粒子の表面活性が強すぎて電解液の分解を抑制する効果が得られない恐れがあるので好ましくない。一方、２次粒子の平均粒径が５μｍ未満では、電極作成時のハンドリングが悪く、１５μｍを超えると電極を均一に作成することが困難になるため好ましくない。
このような１次粒子及び２次粒子の含有割合は、特に限定されず、その粒径が前記範囲であれば良い。
【００１３】
本発明の正極活物質には、酸化物(Ｘ)、酸化物(Ｙ)及び複合体粒子の他に、本発明の所望の目的を損なわない範囲で他の成分が含まれていても良く、また各構成成分において、製造時等に伴なう不可避成分等が含まれていても良い。
【００１４】
本発明の正極活物質の製造方法は、上記本発明の正極活物質が得られれば特に限定されない。例えば、前記酸化物(Ｘ)、これらの複合酸化物又はそれらの原料成分と、前記酸化物(Ｙ)又はそれらの原料成分とを、バインダーと共に造粒又は成形する工程(Ａ)と、工程(Ａ)で得られた造粒物又は成形体を、特定の温度で保持する工程(Ｂ)と、工程(Ｂ)の後、特定の温度で保持する工程(Ｃ)とを含む本発明の製造方法等が挙げられる。
【００１５】
前記工程(Ａ)に用いる、酸化物(Ｘ)は、上述のとおりである。また、それらの原料成分としては、酸化物(Ｘ)又はこれらの複合酸化物の原料成分であれば良く、例えば、Ｃｏ、Ｎｉ及びＦｅからなる群より選択される少なくとも１種の遷移元素；これらの酸化物、水酸化物、塩化物、硝酸塩、硫酸塩等の無機化合物；これらの炭酸塩、蓚酸塩、酢酸塩等の有機化合物；Ｌｉの酸化物、水酸化物、塩化物、硝酸塩、硫酸塩等の無機化合物；これらの炭酸塩、蓚酸塩、酢酸塩等の有機化合物等が挙げられる。
前記工程(Ａ)に用いる、酸化物(Ｙ)としては、上述のとおりである。また、その原料成分としては、酸化物(Ｙ)又はその複合酸化物の原料成分であれば良く、例えば、Ｙｂ；その酸化物、水酸化物、塩化物、硝酸塩、硫酸塩等の無機化合物；これらの炭酸塩、蓚酸塩、酢酸塩等の有機化合物；Ｌｉの酸化物、水酸化物、塩化物、硝酸塩、硫酸塩等の無機化合物；これらの炭酸塩、蓚酸塩、酢酸塩等の有機化合物等が挙げられる。
以上の酸化物(Ｘ)、これらの複合酸化物又はそれらの原料成分と、酸化物(Ｙ)又はそれらの原料成分との造粒又は成形時の配合割合は、上述の本発明の正極活物質における酸化物(Ｘ)及び酸化物(Ｙ)の好ましい含有割合となるように適宜選択して決定することができる。
【００１６】
工程(Ａ)において、上記酸化物(Ｘ)、これらの複合酸化物又はそれらの原料成分と、前記酸化物(Ｙ)又はそれらの原料成分とを造粒又は成形するためのバインダーとしては、粉体を造粒又は成形する際に一般に用いられる公知のバインダーを使用することができる。好ましくは、金属元素を含まないポリビニルアルコール等の有機化合物が好ましい。
この造粒又は成形は、公知の方法等で行うことができ、造粒する場合には、平均粒径が３〜２０ｍｍ、特に５〜１０ｍｍとなるように造粒することが好ましく、成形する場合には、平均厚さ３〜２０ｍｍ、特に５〜１０ｍｍとなるように、例えば、板状等に成形することが好ましい。造粒する場合の平均粒径若しくは成形する場合の厚さが３ｍｍ未満の場合には、後述する焼成時に焼結が進み１次粒子が大きくなりすぎたり、また得られる焼成物が単一相になり所望の効果が得られない恐れがあるので好ましくない。
【００１７】
前記工程(Ｂ)において特定温度とは、工程(Ａ)で得られた造粒物又は成形物中に含まれるＬｉ化合物の少なくとも一部が溶融する温度であって、且つ６００〜８００℃の温度である。この温度は、造粒物又は成形物中のＬｉ化合物の少なくとも一部を溶融し、得られる焼成物にＬｉ化合物をなるべく行き渡らせて、反応を円滑に進ませること、酸化物(Ｘ)と酸化物(Ｙ)とを選択的に生成させること、酸化物(Ｙ)の形状及び分散状態をコントロールしうる温度が好ましく、特に、溶融させるＬｉ化合物の融点直上近辺が望ましい。温度をあまり上げすぎると、溶融したＬｉ化合物の粘度が小さくなりすぎて得られる焼結物外へ漏れ出す恐れがあるので好ましくない。この温度における保持時間は、造粒物又は成形物の大きさや処理量により適宜選択することができる。通常は１０〜３００分間が好ましい。
【００１８】
前記工程(Ｃ)において特定温度とは、工程(Ｂ)における前記保持温度より高く、且つ８００〜１１００℃の温度、好ましくは９００〜１０００℃である。この温度は、酸化物(Ｘ)と酸化物(Ｙ)とを生成させ、また、必要により上述の複合体粒子を生成させる温度である。この工程における温度が、高すぎる場合には、得られる酸化物(Ｘ)、酸化物(Ｙ)や複合体粒子の焼結反応が進み、これらの粒径や粒子形状を制御することが困難になり、また、Ｌｉ成分が揮発飛散して組成バランスが損なわれる恐れがあるため好ましくない。
工程(Ｃ)における前記温度での保持時間は、酸化物(Ｘ)及び酸化物(Ｙ)がそれぞれ均質に生成するのに十分な時間であればよい。短すぎると均質さが損なわれて十分な効果を得ることができず、長すぎると複合体粒子の供給反応が進んで粒子の粒径や粒子形状を制御することが困難になり、また、Ｌｉ成分が揮発飛散して組成バランスが損なわれる恐れがあるため好ましくない。通常は１０〜９００分間が好ましく、特に６０〜５００分間が望ましい。
【００１９】
本発明の非水電解液２次電池は、正極活物質粉末を有する正極と、負極と、電解液とを備え、該正極活物質粉末が、前記本発明の正極活物質を含んでおれば良い。負極及び電解液は公知のものを使用することができ、常法に従って非水電解液２次電池を得ることができる。
【００２０】
【発明の効果】
本発明の非水電解液２次電池用正極活物質は、特定組成の酸化物(Ｘ)と酸化物(Ｙ)とを含むので、非水電解液２次電池における負荷特性の改善が良好で、高容量化が実現できる。
また、本発明の製造方法では、酸化物(Ｘ)、これらの複合酸化物又はそれらの原料成分と、前記酸化物(Ｙ)又はそれらの原料成分とを、バインダーと共に造粒又は成形する工程(Ａ)と、工程(Ａ)で得られた造粒物又は成形体を、特定の温度で保持する工程(Ｂ)と、工程(Ｂ)の後、特定の温度で保持する工程(Ｃ)とを含むので、本発明の正極活物質を効率良く、容易に得ることができる。
更に本発明の非水電解液２次電池は、正極活物質として本発明の正極活物質を含むので、優れた放電容量を有し、リチウムイオン２次電池等に有用である。
【００２１】
【実施例】
以下、実施例及び比較例により本発明を更に詳細に説明するが、本発明はこれらに限定されるものではない。
実施例１
純度９９．８％のコバルトメタル１７０ｇと、酸化イッテルビウム(株式会社三徳製、純度９９．９％)２．８３ｇとを硝酸に溶解した後、純水で希釈し、２８００ｍｌとした。次いで、４Ｎの水酸化ナトリウム溶液１４００ｍｌを加え撹拌した後、ろ過し、水酸化物のケーキを得た。そのケーキを３００℃で４時間焼成し、２３３ｇの複合酸化物を得た。
得られた複合酸化物２３３ｇと、炭酸リチウム１１０ｇと、複合酸化物に対して４０質量％の４質量％ポリビニルアルコール水溶液とを均一に混合した後、造粒機(深江パウテック社製、ハイスピードミキサー)を用いて造粒を行い、平均粒径１０ｍｍの造粒物を調製した。得られた造粒物を、炭酸リチウムの融点以上である７００℃で６０分間仮焼成を行った後、９５０℃で１８０分間本焼成を行い粒子状の焼結物を得た。
得られた焼結物をＩＣＰ発光分光分析装置、Ｘ線回析装置、電子顕微鏡、ＥＳＣＡを用いて調査した結果、一次粒子が０．２〜１μｍであり、二次粒子が８〜９μｍであった。また、焼結物は、ＬｉＣｏＯ2の粒子表面にＬｉＹｂＯ2が均一に分散しているものであり、ＬｉＣｏＯ2及びＬｉＹｂＯ2の含有割合は質量比で９９：１であった。
【００２２】
次に、得られた焼結物である正極活物質粒子と、導電助剤としてアセチレンブラックと、結着剤としてＰＴＦＥとを、質量比で５０：４０：１０の割合で混合し正極合剤を調製し、ステンレス銅板を集電体とした正極を作製した。また、ステンレス鋼板を集電体としたリチウム金属の負極を作製した。更にエチレンカーボネートとジメチルカーボネートとを体積比１：１の割合で混合した溶液に過塩素酸リチウムを１ｍｏｌ／ｌの割合で混合して電解液を調製した。得られた正極、負極及び電解液を用いリチウムイオン二次電池を作製した。
得られた電池を充電電流密度３ｍＡ／ｃｍ2になる条件で充電上限電圧４．３Ｖ、放電下限電圧を３Ｖとして初期放電容量を測定した。結果を表１に示す。
【００２３】
実施例２
酸化イッテルビウムの使用量を５．６６ｇとした以外は実施例１と同様の操作により正極活物質粒子及びリチウムイオン二次電池を作製し、同様な評価を行った。結果を表１に示す。
【００２４】
参考例３
リチウムとイッテリビウムとの原子比が１：１となるように、炭酸リチウムと酸化イッテリビウムとを混合した後、９５０℃で１８０分間焼成し、ＬｉＹｂＯ2を得た。得られたＬｉＹｂＯ2１２ｇ、炭酸リチウム９０．２ｇ、酸化コバルト２００ｇ及び酸化コバルトに対して４０質量％の４質量％ポリビニルアルコール水溶液を均一に混合した後、造粒を行い、平均粒径１０ｍｍの造粒物を調製した。
得られた造粒物を、炭酸リチウムの融点以上である７００℃で６０分間仮焼成した後、９５０℃で１８０分間本焼成を行い粒子状の焼結物を得、更にリチウムイオン２次電池を得、実施例１と同様の評価を行った。結果を表１に示す。
【００２５】
実施例４
参考例３において、酸化物(Ｙ)であるＬｉＹｂＯ2の含有割合における初期放電容量の影響を測定するために、造粒物調製時のＬｉＹｂＯ2の添加量を調整し、得られる正極活物質粒子中のＬｉＹｂＯ2の含有割合が０．０１〜３０質量％となるように変化させて上記と同様に正極活物質粒子を調製した。得られた正極活物質中のＬｉＹｂＯ2の含有割合はＩＰＣ分析により測定した。次に、得られたそれぞれの正極活物質を用いて実施例１と同様にリチウムイオン２次電池を作製し、初期放電容量を測定した。結果を図１に示す。
図１より、酸化物(Ｙ)の含有割合が０．０１〜２０質量％で高い放電容量が得られ、特に０．１〜５質量％程度でより高い放電容量が得られることが判った。また、酸化物(Ｙ)の含有割合が２０質量％を超えると割合が高くなるに従い電容量が低下することが判った。
【００２６】
また、酸化物(Ｙ)であるＬｉＹｂＯ2の粒子径における初期放電容量の影響を測定するために、得られる正極活物質中のＬｉＹｂＯ2粒子の一次粒子径の平均が０．０１μｍ、０．０５μｍ、０．１μｍ、０．２μｍ、０．５μｍ、０．７μｍ、１．０μｍ、１．５μｍ、２．０μｍ、５μｍ、１０μｍ、１５μｍ、２０μｍ、２５μｍ及び３０μｍとなるように参考例３に記載の方法に準じて正極活物質粒子を得、更にリチウムイオン二次電池を作製して各初期放電容量を測定した。結果を図２に示す。
【００２７】
参考例５〜７
酸化イッテリビウムの代わりに、Ｇｄ、Ｃｅ又はＳｍの化合物を用いた以外は、実施例１と同様に正極活物質粒子を得、更にリチウムイオン二次電池を作製して同様な評価を行なった。結果を表１に示す。
【００２８】
参考例８
参考例３と同様な方法で調製したＬｉＹｂＯ2４．２ｇと、炭酸リチウム８４．６ｇと、酸化マンガン２００ｇと、酸化マンガンに対して４０質量％の４質量％ポリビニルアルコール水溶液とを均一に混合した後、造粒を行い、平均粒径１０ｍｍの造粒物を調製した。得られた造粒物を炭酸リチウムの融点以上の７００℃で６０分間仮焼成を行った後、９５０℃で１８０分間本焼成を行い粒状の焼結物を得、実施例１と同様にリチウムイオン二次電池を作製し、同様の評価を行った。結果を表１に示す。
【００２９】
参考例９
参考例８において、仮焼成温度又は本焼成温度の一方を３００〜１０００℃又は６００〜１３００℃の範囲で変化させ、粒状の焼成物及びリチウムイオン２次電池を作製し、それぞれの焼成温度における初期放電容量に対する影響を測定した。本焼成温度を変化させた際の初期放電容量の変化を示す結果を図３に、仮焼成温度を変化させた際の初期放電容量の変化を示す結果を図４にそれぞれ示す。
図３及び４より明らかなように、本焼成温度は８００〜１１００℃が好ましく、仮焼成温度は６００〜８００℃が好ましいことが判った。
【００３０】
参考例１０
水酸化ニッケル、酸化コバルト及び炭酸リチウムを、リチウム、コバルト、ニッケルが原子比で２：１：１になるよう秤量し、それらを均一混合した後、８５０℃で８時間酸素雰囲気中で焼成し、酸化物(Ｘ)であるＬｉＮｉ0.5Ｃｏ0.5Ｏ2を得た。またＮｉ0.9Ｍｎ0.1(ＯＨ)2に、Ｌｉ2Ｃｏ3をＮｉ＋Ｍｎ：Ｌｉが１：１になるよう秤量混合した後、上記と同様な焼成を行い、酸化物(Ｘ)であるＬｉＮｉ0.9Ｍｎ0.1Ｏ2を得た。
次いで、得られたそれぞれの酸化物(Ｘ)に対して、ＬｉＹｂＯ2の割合が５質量％になるように添加し、正極活物質を得た。得られた正極活物質について実施例１と同様に初期放電容量を測定した。その結果、酸化物(Ｘ)としてＬｉＮｉ0.5Ｃｏ0.5Ｏ2を用いた場合には１４５ｍＡｈ／ｇ、ＬｉＮｉ0.9Ｍｎ0.1Ｏ2を用いた場合には１５０ｍＡｈ／ｇであった。これに対して、酸化物(Ｙ)としてのＬｉＹｂＯ2を混合しなかった場合には、共に１３５ｍＡｈ／ｇであった。
【００３１】
比較例１
正極活物質として、酸化物(Ｘ)としてのＬｉＣｏＯ2からなる正極活物質を用いた以外は、実施例１と同様にリチウムイオン二次電池を作製して同様な評価を行なった。結果を表１に示す。
【００３２】
比較例２
正極活物質として、酸化物(Ｘ)としてのＬｉＭｎ2Ｏ4からなる正極活物質を用いた以外は、実施例１と同様にリチウムイオン二次電池を作製して同様な評価を行なった。結果を表１に示す。
【００３３】
【表１】
【図面の簡単な説明】
【図１】 実施例４で行った、酸化物(Ｙ)であるＬｉＹｂＯ2の含有割合における放電容量の影響を測定した結果を示すグラフである。
【図２】 実施例４で行った、酸化物(Ｙ)であるＬｉＹｂＯ2の粒子径における放電容量の影響を測定した結果を示すグラフである。
【図３】 参考例９で行った、本焼成温度を変化させた際の初期放電容量の変化を示すグラフである。仮焼成温度を変化させた際の初期放電容量の変化を示す結果を
【図４】 参考例９で行った、仮焼成温度を変化させた際の初期放電容量の変化を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery active material capable of effectively improving load characteristics and increasing capacity in a secondary battery using a non-aqueous solution as an electrolyte, a method for producing the same, and a non-aqueous solution using the same. The present invention relates to an electrolyte secondary battery.
[0002]
[Prior art]
In recent years, portable electronic devices such as video cameras, portable CDs, cellular phones, PDAs, and notebook personal computers have been reduced in size, weight, and performance. For power sources of these portable electronic devices, secondary batteries having high capacity and excellent heavy load characteristics and high safety are required. Sealed lead-acid batteries and nickel-cadmium batteries have been used as secondary batteries that meet these objectives, but nickel-metal hydride batteries and non-aqueous electrolyte secondary batteries as lithium-ion secondary batteries have higher energy density. Has been put to practical use.
Lithium ion secondary batteries use a composite oxide of lithium and a transition metal such as cobalt, nickel, manganese, etc., as a positive electrode active material, and a carbonaceous material such as carbon that can insert and desorb lithium ions into the negative electrode active material The battery has a feature that it has a larger capacity and a higher voltage than a nickel metal hydride storage battery.
[0003]
[Problems to be solved by the invention]
Lithium ion secondary batteries have the above-mentioned advantages, but have the disadvantage that the high load characteristics are inferior to those of Ni / MH batteries and Ni / Cd batteries. In order to improve the characteristics, the conductive agent in the positive electrode active material is increased, the addition of other elements such as Al as elements constituting the positive electrode active material, atomization of the positive electrode active material, etc. are being studied. In this case, the battery capacity is reduced.
[0004]
Accordingly, an object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can effectively improve the load characteristics of the non-aqueous electrolyte secondary battery and increase the capacity, and a method for producing the same. is there.
Another object of the present invention is to provide a nonaqueous electrolyte secondary battery capable of obtaining an excellent discharge capacity.
[0005]
[Means for Solving the Problems]
According to the present invention, an oxide (X) containing lithium and containing at least one transition element selected from the group consisting of Co, Ni and Fe, or a composite oxide thereof, and LiLnO 2 (wherein , Ln is an oxide (Y) and the including particulate sinter represented by.) showing the Yb, the content is 0.5 to 3 mass oxides in the sintered product (Y) %, A positive electrode active material for a non-aqueous electrolyte secondary battery is provided.
According to the present invention, the oxide (X) containing lithium and containing at least one transition element selected from the group consisting of Co, Ni and Fe, or a composite oxide thereof, and LiLnO 2 (formula (Wherein Ln represents Yb ) and the step (A) of granulating or molding the oxide (Y) represented by
The granulated product or molded product obtained in the step (A) is held at a temperature at which at least a part of the Li compound contained in the granulated product or molded product melts and at a temperature of 600 to 800 ° C. Step (B) to perform,
A positive electrode for a non-aqueous electrolyte secondary battery comprising the step (C) of holding at a temperature higher than the holding temperature in the step (B) and at a temperature of 800 to 1100 ° C. after the step (B) A method for producing an active material is provided.
Furthermore, according to the present invention, a positive electrode having a positive electrode active material powder, a negative electrode, and an electrolyte solution, wherein the positive electrode active material powder is the positive electrode active material for a non-aqueous electrolyte secondary battery, A non-aqueous electrolyte secondary battery is provided.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter referred to as the positive electrode active material of the present invention) contains lithium and contains at least one transition selected from the group consisting of Co, Ni and Fe It is a particulate sintered product containing an oxide (X) containing an element or a composite oxide thereof and an oxide (Y) represented by LiLnO 2 (wherein Ln represents Yb ) .
[0007]
In the positive electrode active material of the present invention, the oxide (Y) has a function of smoothly taking in and out lithium (Li) in the oxide (X), and is considered to contribute to improvement of load characteristics and discharge capacity. It is done. That is, at the time of charge reaction, the Li in the oxide (X) is Li + through the oxide (Y), also discharge upon reaction in the electrolyte Li + is reduced on oxide (Y), oxide It is considered that the load characteristics can be improved and the discharge capacity can be increased because of diffusion into the object (X). Further, non-oxide particles (Y) are dispersed on the particle surface of the oxide particles (X), and composite particles of oxide (X) and oxide (Y) are present in the form of non-oxide. It seems that the affinity with the water electrolyte is improved, and the load characteristics can be improved and the discharge capacity can be increased.
[0008]
In the positive electrode active material of the present invention, the oxide (X) and the oxide (Y) include a form of a mixture of particles, a form in which each primary particle is a secondary particle, and the like. Further, in addition to particles of these forms, composite particles of oxide (X) and oxide (Y) may be included.
As the form of a mixture of the particles, oxides (Y) is, be in the form that existed dispersed on the particle surfaces of oxides (X) is not to prefer in order to further improve the desired effect. In particular, a form oxides (Y) are chemically bonded to the surface of the oxide (X) is preferred.
[0009]
Examples of the oxide (X) or a composite oxide thereof, for example, LiCoO 2, LiNi O 2, Li FeO 2 and, LiCo 0.8 Ni 0.2 O 2, LiNi 0.5 Co 0.5 O 2, LiNi 0.9 Co 0.1 O 2 or the like of LiCo X Ni (1-X) O 2 (0 ≦ X ≦ 1) Ru include oxides represented by.
[0010]
The oxide (Y) is LiYbO 2 .
[0011]
In the present invention, the content ratio of the oxide (Y) with respect to the total amount of the oxide (X) and the oxide (Y) is 0 in order to improve the discharge capacity when a non-aqueous electrolyte secondary battery is obtained. 0.5-3 mass%. Less than 0.01% by mass is not preferable because a desired effect cannot be obtained. Also, Ru danger of capacity reduction due to the decrease of the active material than the improvement of utilization factor of the active material occurs when it exceeds 20 wt%. At this time, when the positive electrode active material of the present invention includes a composite oxide of oxide (X) and oxide (Y), the proportion corresponding to oxide (Y) in the composite oxide is determined as oxide. It is included in the content ratio of (Y).
[0012]
In the positive electrode active material of the present invention, the oxide (X), oxide (Y), and composite particles have a particle size of 90% or more of the primary particles of 1 μm or less, particularly 0.1 to 0. It is preferable that the average particle diameter of the secondary particles as an aggregate of the primary particles is in the range of 5 to 15 μm. In particular, the average particle size of the oxide (Y) is preferably 1 μm or less in order to increase the discharge capacity. As the particle size of the oxide (Y) increases, the effect of addition decreases. That is, it is considered that the diffusion of Li in the oxide (Y) becomes a problem and the effect of addition decreases. If the particle diameter of the primary particles is less than 0.1 μm, the surface activity of the particles is too strong, and the effect of suppressing the decomposition of the electrolytic solution may not be obtained. On the other hand, when the average particle size of the secondary particles is less than 5 μm, handling at the time of electrode preparation is poor, and when it exceeds 15 μm, it is difficult to uniformly form the electrode, which is not preferable.
The content ratio of such primary particles and secondary particles is not particularly limited as long as the particle diameter is in the above range.
[0013]
The positive electrode active material of the present invention may contain other components in addition to the oxide (X), oxide (Y) and composite particles as long as the desired purpose of the present invention is not impaired. In addition, in each constituent component, inevitable components and the like that accompany production are included.
[0014]
The method for producing the positive electrode active material of the present invention is not particularly limited as long as the positive electrode active material of the present invention is obtained. For example, the step (A) of granulating or molding the oxide (X), a composite oxide thereof or a raw material component thereof, and the oxide (Y) or a raw material component thereof together with a binder, The production of the present invention comprising the step (B) of holding the granulated product or the molded product obtained in A) at a specific temperature and the step (C) of holding the granule or the molded body at a specific temperature after the step (B). Methods and the like.
[0015]
The oxide (X) used in the step (A) is as described above . In addition, the raw material component may be a raw material component of oxide (X) or a composite oxide thereof, for example, at least one transition element selected from the group consisting of Co, Ni and Fe; Inorganic compounds such as oxides, hydroxides, chlorides, nitrates and sulfates; organic compounds such as carbonates, oxalates and acetates; oxides of hydroxides, hydroxides, chlorides, nitrates and sulfuric acids Inorganic compounds such as salts; organic compounds such as carbonates, oxalates, and acetates thereof.
The oxide (Y) used in the step (A) is as described above . Further, examples of the raw material components may be a raw material components in the oxide (Y) or a composite oxide thereof, for example, Yb; their oxides, hydroxides, chlorides, nitrates, inorganic compounds such as sulfates; Organic compounds such as carbonates, oxalates and acetates; inorganic compounds such as Li oxides, hydroxides, chlorides, nitrates and sulfates; Organic compounds such as carbonates, oxalates and acetates Etc.
The above-mentioned oxide (X), these composite oxides or their raw material components, and the blending ratio of the oxide (Y) or their raw material components at the time of granulation or molding is the positive electrode active material of the present invention described above It can be determined by appropriately selecting so as to have a preferable content ratio of oxide (X) and oxide (Y).
[0016]
In the step (A), the oxide (X), these composite oxides or their raw material components, and the binder for granulating or molding the oxide (Y) or their raw material components are powders. Known binders generally used in granulating or molding the body can be used. Preferably, an organic compound such as polyvinyl alcohol containing no metal element is preferable.
This granulation or molding can be performed by a known method or the like. When granulating, it is preferable to granulate so that the average particle diameter is 3 to 20 mm, particularly 5 to 10 mm. For example, it is preferable to form a plate or the like so that the average thickness is 3 to 20 mm, particularly 5 to 10 mm. When the average particle diameter when granulating or the thickness when molding is less than 3 mm, the sintering proceeds at the time of firing, which will be described later, and the primary particles become too large, or the obtained fired product becomes a single phase. This is not preferable because a desired effect may not be obtained.
[0017]
The specific temperature in the step (B) is a temperature at which at least a part of the Li compound contained in the granulated product or molded product obtained in the step (A) melts, and a temperature of 600 to 800 ° C. It is. This temperature melts at least a part of the Li compound in the granulated product or molded product, spreads the Li compound as much as possible in the obtained fired product, and facilitates the reaction, and the oxide (X) and the oxidation. A temperature at which the product (Y) can be selectively generated and the shape and dispersion state of the oxide (Y) can be controlled is preferable, and particularly near the melting point of the Li compound to be melted. If the temperature is raised too much, the viscosity of the molten Li compound becomes too small, and it may leak out of the sintered product obtained, which is not preferable. The holding time at this temperature can be appropriately selected depending on the size or the processing amount of the granulated product or molded product. Usually, 10 to 300 minutes are preferable.
[0018]
In the step (C), the specific temperature is higher than the holding temperature in the step (B) and a temperature of 800 to 1100 ° C, preferably 900 to 1000 ° C. This temperature is a temperature at which the oxide (X) and the oxide (Y) are generated and, if necessary, the above composite particles are generated. If the temperature in this step is too high, the sintering reaction of the resulting oxide (X), oxide (Y) and composite particles proceeds, making it difficult to control the particle size and particle shape of these. In addition, the Li component volatilizes and scatters and the composition balance may be impaired.
The holding time at the above temperature in the step (C) may be sufficient as long as the oxide (X) and the oxide (Y) are uniformly formed. If it is too short, homogeneity is impaired and a sufficient effect cannot be obtained, and if it is too long, the supply reaction of the composite particles proceeds and it becomes difficult to control the particle size and particle shape of the particles. This is not preferable because the components may be volatilized and scattered to impair the composition balance. Usually, 10 to 900 minutes are preferable, and 60 to 500 minutes is particularly desirable.
[0019]
The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode having a positive electrode active material powder, a negative electrode, and an electrolyte solution, and the positive electrode active material powder may contain the positive electrode active material of the present invention. . A well-known thing can be used for a negative electrode and electrolyte solution, and a nonaqueous electrolyte secondary battery can be obtained according to a conventional method.
[0020]
【Effect of the invention】
Since the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention contains the oxide (X) and the oxide (Y) having a specific composition, the load characteristics in the non-aqueous electrolyte secondary battery are improved. High capacity can be realized.
In the production method of the present invention, the oxide (X), these composite oxides or their raw material components, and the oxide (Y) or their raw material components are granulated or molded together with a binder ( A), the step (B) of holding the granulated product or the molded product obtained in the step (A) at a specific temperature, and the step (C) of holding the specific temperature after the step (B). Therefore, the positive electrode active material of the present invention can be obtained efficiently and easily.
Furthermore, since the non-aqueous electrolyte secondary battery of the present invention includes the positive electrode active material of the present invention as the positive electrode active material, it has an excellent discharge capacity and is useful for lithium ion secondary batteries and the like.
[0021]
【Example】
Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these.
Example 1
170 g of cobalt metal having a purity of 99.8% and 2.83 g of ytterbium oxide (manufactured by Santoku Co., Ltd., purity 99.9%) were dissolved in nitric acid and then diluted with pure water to make 2800 ml. Subsequently, 1400 ml of 4N sodium hydroxide solution was added and stirred, followed by filtration to obtain a hydroxide cake. The cake was baked at 300 ° C. for 4 hours to obtain 233 g of a composite oxide.
After uniformly mixing 233 g of the obtained composite oxide, 110 g of lithium carbonate, and 40% by weight of a 4% by weight polyvinyl alcohol aqueous solution with respect to the composite oxide, a granulator (manufactured by Fukae Pautech Co., Ltd., high speed mixer). ) Was used to prepare a granulated product having an average particle size of 10 mm. The obtained granulated material was temporarily fired at 700 ° C., which is equal to or higher than the melting point of lithium carbonate, for 60 minutes, and then fired at 950 ° C. for 180 minutes to obtain a particulate sintered product.
As a result of investigating the obtained sintered product using an ICP emission spectroscopic analyzer, an X-ray diffraction apparatus, an electron microscope, and ESCA, the primary particles were 0.2 to 1 μm and the secondary particles were 8 to 9 μm. It was. In the sintered product, LiYbO 2 was uniformly dispersed on the surface of the LiCoO 2 particles, and the content ratio of LiCoO 2 and LiYbO 2 was 99: 1 by mass ratio.
[0022]
Next, the positive electrode active material particles as the obtained sintered product, acetylene black as a conductive additive, and PTFE as a binder are mixed in a mass ratio of 50:40:10 to obtain a positive electrode mixture. A positive electrode was prepared using a stainless copper plate as a current collector. In addition, a lithium metal negative electrode using a stainless steel plate as a current collector was prepared. Further, an electrolytic solution was prepared by mixing lithium perchlorate at a ratio of 1 mol / l to a solution in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 1. A lithium ion secondary battery was fabricated using the obtained positive electrode, negative electrode, and electrolytic solution.
The initial discharge capacity of the obtained battery was measured under the condition that the charge current density was 3 mA / cm 2 and the charge upper limit voltage was 4.3 V and the discharge lower limit voltage was 3 V. The results are shown in Table 1.
[0023]
Example 2
Except that the amount of ytterbium oxide used was 5.66 g, positive electrode active material particles and a lithium ion secondary battery were produced in the same manner as in Example 1, and the same evaluation was performed. The results are shown in Table 1.
[0024]
Reference example 3
Lithium carbonate and ytterbium oxide were mixed so that the atomic ratio of lithium to ytterbium was 1: 1, and then baked at 950 ° C. for 180 minutes to obtain LiYbO 2 . After 12 g of LiYbO 2 thus obtained, 90.2 g of lithium carbonate, 200 g of cobalt oxide and 40% by mass of 4% by mass of a polyvinyl alcohol aqueous solution were mixed uniformly with respect to cobalt oxide, granulation was performed, and granulation was performed with an average particle size of 10 mm. Granules were prepared.
The obtained granulated material was calcined for 60 minutes at 700 ° C., which is equal to or higher than the melting point of lithium carbonate, and then calcined at 950 ° C. for 180 minutes to obtain a particulate sintered product. The same evaluation as in Example 1 was performed. The results are shown in Table 1.
[0025]
Example 4
In Reference Example 3 , in order to measure the influence of the initial discharge capacity on the content ratio of LiYbO 2 which is the oxide (Y), the amount of LiYbO 2 added during granule preparation is adjusted, and the resulting positive electrode active material particles Positive electrode active material particles were prepared in the same manner as described above while changing the content ratio of LiYbO 2 in the solution to 0.01 to 30% by mass. The content ratio of LiYbO 2 in the obtained positive electrode active material was measured by IPC analysis. Next, a lithium ion secondary battery was produced in the same manner as in Example 1 using each of the obtained positive electrode active materials, and the initial discharge capacity was measured. The results are shown in FIG.
From FIG. 1, it was found that a high discharge capacity was obtained when the content ratio of the oxide (Y) was 0.01 to 20% by mass, and a higher discharge capacity was obtained particularly when the content was about 0.1 to 5% by mass. Further, it was found that when the content ratio of the oxide (Y) exceeds 20% by mass, the electric capacity decreases as the ratio increases.
[0026]
Moreover, in order to measure the influence of the initial discharge capacity on the particle diameter of LiYbO 2 which is oxide (Y), the average primary particle diameter of LiYbO 2 particles in the obtained positive electrode active material is 0.01 μm, 0.05 μm. 0.1 μm, 0.2 μm, 0.5 μm, 0.7 μm, 1.0 μm, 1.5 μm, 2.0 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm and 30 μm as described in Reference Example 3 According to the method, positive electrode active material particles were obtained, and a lithium ion secondary battery was prepared to measure each initial discharge capacity. The results are shown in FIG.
[0027]
Reference Examples 5-7
Cathode active material particles were obtained in the same manner as in Example 1 except that a compound of Gd, Ce or Sm was used instead of ytterbium oxide, and a lithium ion secondary battery was prepared and evaluated in the same manner. The results are shown in Table 1.
[0028]
Reference Example 8
LiYbO 2 4.2 g prepared by the same method as in Reference Example 3 , lithium carbonate 84.6 g, manganese oxide 200 g, and 40% by mass of 4% by mass polyvinyl alcohol aqueous solution with respect to manganese oxide were uniformly mixed. Thereafter, granulation was performed to prepare a granulated product having an average particle size of 10 mm. The obtained granulated material was calcined for 60 minutes at 700 ° C., which is equal to or higher than the melting point of lithium carbonate, and then calcined for 180 minutes at 950 ° C. to obtain a granular sintered product. A secondary battery was produced and evaluated in the same manner. The results are shown in Table 1.
[0029]
Reference Example 9
In Reference Example 8 , one of the preliminary calcination temperature or the main calcination temperature is changed in the range of 300 to 1000 ° C. or 600 to 1300 ° C. to produce a granular fired product and a lithium ion secondary battery, and the initial stage at each firing temperature. The effect on the discharge capacity was measured. FIG. 3 shows the results showing the change in the initial discharge capacity when the main firing temperature is changed, and FIG. 4 shows the results showing the change in the initial discharge capacity when the temporary firing temperature is changed.
As apparent from FIGS. 3 and 4, it was found that the main baking temperature is preferably 800 to 1100 ° C., and the temporary baking temperature is preferably 600 to 800 ° C.
[0030]
Reference Example 10
Nickel hydroxide, cobalt oxide, and lithium carbonate were weighed so that lithium, cobalt, and nickel had an atomic ratio of 2: 1: 1, and they were uniformly mixed, and then calcined at 850 ° C. for 8 hours in an oxygen atmosphere. LiNi 0.5 Co 0.5 O 2 which is an oxide (X) was obtained. In addition, Li 2 Co 3 was weighed and mixed with Ni 0.9 Mn 0.1 (OH) 2 so that Ni + Mn: Li was 1: 1, and then fired in the same manner as described above to obtain the oxide (X) LiNi 0.9 Mn 0.1. O 2 was obtained.
Then, respective oxides obtained for (X), was added as the proportion of LiYbO 2 becomes 5 mass% to obtain a positive electrode active material. The initial discharge capacity of the obtained positive electrode active material was measured in the same manner as in Example 1. As a result, it was 145 mAh / g when LiNi 0.5 Co 0.5 O 2 was used as the oxide (X), and 150 mAh / g when LiNi 0.9 Mn 0.1 O 2 was used. On the other hand, when LiYbO 2 as the oxide (Y) was not mixed, it was 135 mAh / g in both cases.
[0031]
Comparative Example 1
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that a positive electrode active material made of LiCoO 2 as the oxide (X) was used as the positive electrode active material. The results are shown in Table 1.
[0032]
Comparative Example 2
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that a positive electrode active material composed of LiMn 2 O 4 as the oxide (X) was used as the positive electrode active material. The results are shown in Table 1.
[0033]
[Table 1]
[Brief description of the drawings]
1 is a graph showing the results of measuring the influence of discharge capacity on the content ratio of LiYbO 2 which is an oxide (Y), performed in Example 4. FIG.
2 is a graph showing the results of measuring the influence of discharge capacity on the particle diameter of LiYbO 2 which is an oxide (Y), performed in Example 4. FIG.
FIG. 3 is a graph showing changes in initial discharge capacity when the main firing temperature is changed, performed in Reference Example 9 ; FIG. 4 is a graph showing the change in the initial discharge capacity when the pre-baking temperature is changed, performed in Reference Example 9, with the results showing the change in the initial discharge capacity when the pre-baking temperature is changed.
Claims (7)
工程(Ａ)で得られた造粒物又は成形体を、該造粒物又は成形体中に含まれるＬｉ化合物の少なくとも一部が溶融する温度であって、且つ６００〜８００℃の温度で保持する工程(Ｂ)と、
工程(Ｂ)の後、該工程(Ｂ)における保持温度より高く、且つ８００〜１１００℃の温度で保持する工程(Ｃ)とを含むことを特徴とする請求項１記載の非水電解液２次電池用正極活物質の製造方法。An oxide (X) containing lithium and containing at least one transition element selected from the group consisting of Co, Ni and Fe, or a composite oxide thereof; and LiLnO 2 (wherein Ln represents Yb ) Step (A) of granulating or molding the oxide (Y) represented by
The granulated product or molded product obtained in the step (A) is held at a temperature at which at least a part of the Li compound contained in the granulated product or molded product melts and at a temperature of 600 to 800 ° C. Step (B) to perform,
The non-aqueous electrolyte 2 according to claim 1, further comprising a step (C) of holding at a temperature higher than the holding temperature in the step (B) and at a temperature of 800 to 1100 ° C. after the step (B). A method for producing a positive electrode active material for a secondary battery.
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| PCT/JP2001/007406 WO2002019449A1 (en) | 2000-08-29 | 2001-08-29 | Positive active material for non-aqueous electrolyte secondary cell, method for preparation thereof and non-aqueous electrolyte secondary cell |
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| JP4967217B2 (en) * | 2003-12-08 | 2012-07-04 | 日本電気株式会社 | Positive electrode active material for secondary battery, positive electrode for secondary battery and secondary battery using the same |
| JP4876371B2 (en) * | 2004-01-29 | 2012-02-15 | 日亜化学工業株式会社 | Positive electrode active material for non-aqueous electrolyte secondary battery, positive electrode mixture for non-aqueous electrolyte secondary battery, and non-aqueous electrolyte secondary battery |
| JP2005339886A (en) * | 2004-05-25 | 2005-12-08 | Sanyo Electric Co Ltd | Nonaqueous electrolyte secondary battery |
| JP5619412B2 (en) * | 2009-09-04 | 2014-11-05 | 三洋電機株式会社 | Non-aqueous electrolyte secondary battery and method for producing non-aqueous electrolyte secondary battery |
| WO2013002369A1 (en) * | 2011-06-30 | 2013-01-03 | 三洋電機株式会社 | Non-aqueous electrolyte secondary cell, and method for producing same |
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| JP3003431B2 (en) * | 1992-11-10 | 2000-01-31 | 松下電器産業株式会社 | Non-aqueous electrolyte secondary battery |
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