JP2004292264A - Trimanganese tetroxide particle, its production method, nonaqueous electrolyte secondary battery, positive electrode active substance therefor and its preparation method - Google Patents
Trimanganese tetroxide particle, its production method, nonaqueous electrolyte secondary battery, positive electrode active substance therefor and its preparation method Download PDFInfo
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Abstract
Description
【０００１】
【産業上の利用分野】
本発明は、非水電解液二次電池用の正極活物質として二次電池の充放電サイクル特性に優れたマンガン酸リチウム粒子粉末に関するものである。
【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。また、電気自動車、ハイブリット車、燃料電池等の自動車、バックアップ電源用などの中・大型電池においても期待されている。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、ジグザグ層状構造のＬｉＭｎＯ２、岩塩型層状構造のＬｉＣｏＯ２、ＬｉＣｏ１−ＸＮｉＸＯ２、ＬｉＮｉＯ２等が一般的に知られており、なかでもＬｉＣｏＯ２は高電圧と高容量を有する点で優れているが、コバルト原料の供給量が少ないことによる製造コスト高の問題や廃棄電池の環境安全上の問題及び構造が不安定なことによる熱安定性の問題が存在する。
【０００４】
そこで、供給量が多く低コストで環境適性がよく安全面でも優れているマンガンを原料として作られるスピネル構造型のマンガン酸リチウム粒子粉末（基本組成：ＬｉＭｎ２Ｏ４−以下、同じ−）の研究が盛んに行われている。
【０００５】
周知の通り、マンガン酸リチウム粒子粉末は、マンガン化合物とリチウム化合物とを所定の割合で混合し、５００〜１０００℃の温度範囲で焼成することによって得ることができる。
【０００６】
しかしながら、マンガン酸リチウム粒子粉末をリチウムイオン二次電池の正極活物質として用いた場合、高電圧と高エネルギー密度を有するものの、充放電サイクル特性が劣るという問題がある。この原因は、充放電中に結晶構造中のＭｎが溶出することに伴う構造の崩壊、また、マンガン酸リチウムは組成により特性が決まるため組成の不均一化による構造劣化等が挙げられる。
【０００７】
マンガン酸リチウム粒子粉末を用いたリチウムイオン二次電池にあっては、充放電の繰り返しによる充放電容量の劣化を抑制し、充放電サイクル特性を向上させることが現在最も要求されている。
【０００８】
充放電サイクル特性を向上させるためには、マンガン酸リチウム粒子粉末からなる正極活物質が充填性に優れ、適度な大きさを有することが必要である。その手段としては、マンガン酸リチウム粒子の粒子径及び粒度分布を制御する方法、焼成温度を制御して高結晶のマンガン酸リチウム粒子粉末を得る方法、異種元素を添加して結晶の結合力を強化する方法、表面処理を行ってＭｎの溶出を抑制する方法等が行われている。
【０００９】
適度な大きさのマンガン酸リチウム粒子粉末を得る方法として、特許文献１乃至２３記載の各方法が知られている。
【００１０】
【特許文献１】
特開平１０−１６２８２６号公報
【特許文献２】
特開平１０−１７２５６７号公報
【特許文献３】
特開平１０−１８２１５９号公報
【特許文献４】
特開平１０−２５５７９７号公報
【特許文献５】
特開平１０−３２１２２７号公報
【特許文献６】
特開平１１−１３２３号公報
【特許文献７】
特開平１１−７１１１５号公報
【特許文献８】
特開平１１−１５７８４１号公報
【特許文献９】
特開平１１−１８０７１７号公報
【特許文献１０】
特開平１１−２１９７０５号公報
【特許文献１１】
特開平１１−２３３１１２号公報
【特許文献１２】
特開２０００−１２０３１号公報
【特許文献１３】
特開２０００−１４３２４７号公報
【特許文献１４】
特開２０００−２１５８９５号公報
【特許文献１５】
特開２０００−２２３１１８号公報
【特許文献１６】
特開２０００−２８１３４９号公報
【特許文献１７】
特開２０００−２８１３５１号公報
【特許文献１８】
特開２００１−２６４２５号公報
【特許文献１９】
特開２００１−９３５２７号公報
【特許文献２０】
特開２００１−１１４５２１号公報
【特許文献２１】
特開２００１−１２２６２６号公報
【特許文献２２】
特開２００１−２４０４１７号公報
【特許文献２３】
特開２００２−１９８０４７号公報
【００１１】
【発明が解決しようとする課題】
非水電解液二次電池用の正極活物質として二次電池の充放電サイクル特性に優れたマンガン酸リチウム粒子粉末は未だ得られていない。
【００１２】
即ち、前出特許文献１には噴霧熱分解法によって粒度分布に優れたマンガン酸リチウム粒子粉末を得る製造法が開示されているが、得られるマンガン酸リチウム粒子粉末は多孔性であり比表面積が大きくなるため、Ｍｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００１３】
また、前出特許文献２には、マンガン化合物とリチウム化合物とのスラリーをスプレードライヤーで乾燥した後、焼成する製造法が開示されているが、多数の一次粒子からなる凝集体を構成しており、比表面積が大きくなるためＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００１４】
また、前出特許文献３には、実施例として５００ｐｐｍのＳ分を含む四酸化三マンガンを用いたマンガン酸リチウムが記載されているが、多量のＳを含有しており、二次電池の充放電サイクル特性の改善には十分とは言い難いものである。
【００１５】
また、前出特許文献４には平均板径１〜５０μｍであって平均板厚０．２〜２μｍであって板径／板厚の比が３以上の板状粒子である酸化マンガン、オキシ水酸化マンガン、水酸化マンガンとリチウム塩とを混合し加熱することでサイクル耐久性に優れたリチウムマンガン複合酸化物を得る製造方法が開示されているが、得られるリチウムマンガン複合酸化物は粒子サイズが小さく比表面積が大きくなるためＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００１６】
また、前出特許文献５には一次粒子と二次粒子の平均粒子径を特定したマンガン酸リチウム粒子粉末が開示されているが、一次粒子が小さく二次粒子は多数の一次粒子によって構成されているため、比表面積が大きくなってＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００１７】
また、前出特許文献６には一次粒子と二次粒子の平均粒子径を特定したマンガン酸リチウム粒子粉末が記載されているが、凝集体であって、比表面積が大きくなるためＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また実施例では平均一次粒子径２．０μｍであって平均二次粒子径２．０μｍであるマンガン酸リチウム粒子粉末が記載されているが、平均粒子径が小さく充填性が十分とは言い難いものである。
【００１８】
また、前出特許文献７には平均凝集粒子径が１〜５０μｍであって平均一次粒子径が３．０μｍ以下であるマンガン酸リチウム粒子粉末が開示されているが、実施例で得られているマンガン酸リチウム粒子の平均一次粒子径は１．０μｍ以下と小さく比表面積が大きくなるため、Ｍｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。
【００１９】
また、前出特許文献８には比表面積が０．３〜０．７ｍ２／ｇであってＳＯ４含有量が０．４重量％以下であるマンガン酸リチウム粒子粉末が記載されているが、ＭｎＯ２を原料としているため、一次粒子が小さく、また、実施例で示されているＳ含有量では特性改善が十分とは言い難いものである。
【００２０】
また、前出特許文献９にはキュービックな粒子形状を有し、０．０１〜１０μｍの粒子径で、１〜１００ｍ２／ｇの範囲の比表面積を有するマンガン酸リチウム粒子粉末が開示されているが、粒子内に空隙を有しているので比表面積が大きく、また、水熱処理をしているため一次粒子が小さく特性改善が十分とは言い難いものである。
【００２１】
また、前出特許文献１０には平均粒子径が１．０μｍ以下の微細粒子の含有量が少ないマンガン酸リチウム粒子粉末が開示されているが、一次粒子については考慮されておらず、マンガン原料に電解ＭｎＯ２を用いていること及び平均粒子径に対する比表面積が大きいことから、凝集粒子であると推測され、Ｍｎの溶出を抑制することは困難であり、結果として、二次電池の充放電サイクル特性が低下する。
【００２２】
また、前出特許文献１１には、ＭｎＳＯ４水和物に水を加えて水溶液濃度を調整し、加熱した後、過酸化水素を滴下し、アンモニア水を加えて洗浄・乾燥を行うことで得られるオキシ水酸化マンガンと水酸化リチウムとを水熱処理することで充放電特性を改善したマンガン酸リチウムが得られることが開示してあるが、一次粒子が小さく比表面積が大きいため、Ｍｎの溶出を抑制することが困難であり、結果として二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００２３】
また、前出特許文献１２には平均粒子径が１〜４５μｍのマンガン酸リチウム粒子粉末が開示されているが、一次粒子については考慮されておらず、得られたマンガン酸リチウム粒子は小さな一次粒子が凝集した二次粒子であるため、比表面積が大きくＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。
【００２４】
また、前出特許文献１３には一次粒子径が０．５〜２．０μｍであるマンガン酸リチウム粒子粉末が開示されているが、一次粒子が小さいため、充填密度が低くなり、また、比表面積も大きくなるためＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。
【００２５】
また、前出特許文献１４には、Ｓの含有量がＳＯ４イオン換算で０．６重量％以下で比表面積０．５〜３ｍ２／ｇ、平均粒径１〜４５μｍのスピネル型リチウムマンガン酸化物が開示されているが、ＣＭＤ（化学合成二酸化マンガン）を用いているため一次粒子が小さく特性改善が十分とは言い難いものである。
【００２６】
また、前出特許文献１５には炭酸リチウムと二酸化マンガンを混合焼成して１０μｍ以上１００μｍ以下のリチウム酸化物が得られることが開示されているが、凝集粒子であり一次粒子が小さく比表面積が大きくなるため、Ｍｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００２７】
また、前出特許文献１６及び１７には球状の炭酸マンガンを窒素雰囲気中で熱処理することで得られるメジアン径が１０μｍ以下の酸化マンガンとリチウム化合物を混合・焼成し得られるメジアン径が１０μｍ以下、タップ密度が１．８ｇ／ｃｍ３以上であるリチウムマンガン酸化物が得られることが開示されているが、炭酸マンガンを原料にしているため、一次粒子が小さく比表面積が大きくなってＭｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。
【００２８】
また、前出特許文献１８にはＮａ含有量を低減した平均粒径３〜２０μｍの電解二酸化マンガンをリチウム原料と混合・焼成することで良好な電池特性を有するマンガン酸リチウムが得られることが開示されているが、電解二酸化マンガンを原料に用いているため、平均粒子径に対する比表面積の値が大きく、Ｍｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。
【００２９】
また、前出特許文献１９には、マンガン錯塩を生成させてから水酸化マンガンを析出させ、４０〜４００℃の気流中で酸化させ、四酸化三マンガンを得た後リチウム化合物と混合・焼成することで得られる非水電解質二次電池用正極活物質が開示されているが、一次粒子が小さく特性改善が十分とは言い難いものである。
【００３０】
また、前出特許文献２０には、マンガンイオンと錯化剤を反応させマンガン錯塩を形成させ、次いでアルカリ金属水酸化物と反応させ水酸化マンガンを生成させたあと、酸化剤と反応させ四酸化三マンガンを得ることが開示されているが、一次粒子が小さく特性改善には十分とは言い難いものである。
【００３１】
また、前出特許文献２１には粒度分布を特定したマンガン酸リチウム粒子粉末が開示されているが、一次粒子については考慮されておらず、マンガン原料に電解二酸化マンガン（ＥＭＤ）又はＣＭＤを用いていること及び平均粒子径に対する比表面積が大きいことから、凝集粒子であると推測され、Ｍｎの溶出を抑制することが困難となり、結果として充放電サイクル特性が低下する。
【００３２】
また、前出特許文献２２にはマンガン酸化物シードを溶液中で得、マンガン酸化物と塩基性化合物とを反応させ、酸化し粒子成長させ、その後、リチウム化合物と反応させるか、プロトン置換させて、結晶性に優れ粒子径が大きく粒度分布が均一であるマンガン酸リチウムの製造法が開示されているが、実施例で硫酸マンガンと水酸化ナトリウムを添加し、マンガン酸化物シードを成長させる工程が記載されているが、反応がｐＨ６．４で終了しており、この領域ではＳ成分が吸着し、残存するＳ量が高いと推測され、また、粒子サイズに対する比表面積の値が大きいことから、Ｍｎの溶出を抑制することが困難となり、結果として、二次電池の充放電サイクル特性が低下する。また、充填密度についても十分とは言い難いものである。
【００３３】
また、前出特許文献２３にはリチウムマンガン複合酸化物中の硫黄含有量が２％以下であることを特徴とするリチウム二次電池及びその製造法が開示されているが、実施例ではＳ含有量が１〜２％の電解二酸化マンガンを用いて正極を作製しており、特性改善には十分とは言い難いものである。
【００３４】
そこで本発明は、非水電解液二次電池用の正極活物質として二次電池の充放電サイクル特性に優れたマンガン酸リチウム粒子粉末を提供することを技術的課題とする。
【００３５】
【課題を解決するための手段】
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。
【００３６】
即ち、本発明は、平均一次粒子が３．０〜１５μｍであり、Ｎａ含有量が０．０２重量％以下、Ｓ含有量が０．０１重量％以下であって、粒子形状が三角状、四角状又は六角状の面をもつ多面体である四酸化三マンガン粒子粉末である（本発明１）。
【００３７】
また、本発明は、マンガン塩水溶液をアルカリ水溶液により中和してマンガン水酸化物を含有する水懸濁液とし、次いで、６０〜１００℃の温度範囲で酸化反応を行って四酸化三マンガン核粒子を得る一次反応を行い、該一次反応後の反応溶液にマンガン塩水溶液を添加した後、酸化反応を行って前記四酸化三マンガン核粒子の成長反応を行う二次反応によって四酸化三マンガン粒子を得る製造法において、一次反応のマンガン濃度を１．５ｍｏｌ／Ｌ以下にするとともに、二次反応のマンガン添加量を一次反応のマンガン濃度の等モル以下にすることを特徴とする前記四酸化三マンガン粒子粉末の製造法である（本発明２）。
【００３８】
また、本発明は、マンガン塩水溶液をアルカリ水溶液により中和してマンガン水酸化物を含有する水懸濁液とし、次いで、６０〜１００℃の温度範囲で酸化反応を行って四酸化三マンガン核粒子を得る一次反応を行い、該一次反応後の反応溶液にマンガン塩水溶液を添加した後、酸化反応を行って前記四酸化三マンガン核粒子の成長反応を行う二次反応によって四酸化三マンガン粒子を得る製造法において、一次反応終了後の反応溶液を非酸化性雰囲気に切り替えた後、マンガン塩水溶液を添加し、次いで、３時間以内の熟成を行うことを特徴とする前記四酸化三マンガン粒子粉末の製造法である（本発明３）。
【００３９】
また、本発明は、マンガン塩水溶液をアルカリ水溶液により中和してマンガン水酸化物を含有する水懸濁液とし、次いで、６０〜１００℃の温度範囲で酸化反応を行って四酸化三マンガン核粒子を得る一次反応を行い、該一次反応後の反応溶液にマンガン塩水溶液を添加した後、酸化反応を行って前記四酸化三マンガン核粒子の成長反応を行う二次反応によって四酸化三マンガン粒子を得る製造法において、反応中にマンガンに対して０．５モル％以下の有機還元剤を存在させることを特徴とする前記四酸化三マンガン粒子粉末の製造法である（本発明４）。
【００４０】
また、本発明は、マンガン塩水溶液をアルカリ水溶液により中和してマンガン水酸化物を含有する水懸濁液とし、次いで、６０〜１００℃の温度範囲で酸化反応を行って四酸化三マンガン核粒子を得る一次反応を行い、該一次反応後の反応溶液にマンガン塩水溶液を添加した後、酸化反応を行って前記四酸化三マンガン核粒子の成長反応を行う二次反応によって四酸化三マンガン粒子を得る製造法において、過剰アルカリ濃度を１．０〜５．０ｍｏｌ／Ｌにすることを特徴とする前記四酸化三マンガン粒子粉末の製造法である（本発明５）。
【００４１】
また、本発明は、マンガン塩水溶液をアルカリ水溶液により中和してマンガン水酸化物を含有する水懸濁液とし、次いで、６０〜１００℃の温度範囲で酸化反応を行って四酸化三マンガン核粒子を得る一次反応を行い、該一次反応終了後、非酸化性雰囲気に切り替えた後の反応溶液に一次反応で用いたマンガンに対して等モル以下のマンガン塩水溶液を添加し、３ｈ以内の熟成を行った後、酸化反応を行って前記四酸化三マンガン核粒子の成長反応を行う二次反応によって四酸化三マンガン粒子を得る製造法において、一次反応のマンガン濃度を１．５ｍｏｌ／Ｌ以下にするとともに、反応中に有機還元剤をマンガンに対して０．５モル％以下存在させ、過剰アルカリ濃度を１．０〜５ｍｏｌ／Ｌとすることを特徴とする前記四酸化三マンガン粒子粉末の製造法である（本発明６）。
【００４２】
また、本発明は、平均一次粒子径が３．０〜１５μｍであり、Ｎａ含有量が０．０３重量％以下、Ｓ含有量が０．０１重量％以下であって粒子形状が等方的多面体であるマンガン酸リチウム粒子粉末からなることを特徴とする非水電解質二次電池用正極活物質である（本発明７）。
【００４３】
また、本発明は、前記四酸化三マンガン粒子粉末とリチウム化合物を混合し、５００℃〜１０００℃で熱処理することを特徴とする請求項８記載の非水電解質二次電池用正極活物質の製造方法である（本発明８）。
【００４４】
また、本発明は、前記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（本発明９）。
【００４５】
次に、本発明の構成をより詳しく説明すれば次の通りである。
【００４６】
先ず、本発明１に係る四酸化三マンガン粒子粉末について述べる。
【００４７】
なお、本発明において、「一次粒子」とは単独で存在することができる最小粒子を表す。
【００４８】
本発明１に係る四酸化三マンガン粒子粉末は、平均一次粒子径が３．０〜１５μｍである。平均一次粒子径が３．０μｍ未満の場合には、該四酸化三マンガン粒子粉末を用いて得られるマンガン酸リチウム粒子粉末を二次電池の正極として製造する際に充填密度が低くなり、エネルギー密度が低下する。平均一次粒子径が１５μｍ以上の場合には、該四酸化三マンガン粒子粉末を用いて得られるマンガン酸リチウム粒子粉末を二次電池の正極として用いた場合に電流密度を増加させた場合にＬｉの脱挿入反応が低下する傾向がある。好ましくは３．０〜１２μｍである。
【００４９】
本発明１に係る四酸化三マンガン粒子粉末は、Ｎａ含有量が０．０３重量％以下、Ｓ含有量が０．０１重量％以下である。Ｎａ含有量及びＳ含有量が前記範囲を超える場合は、該四酸化三マンガン粒子粉末を用いて得られるマンガン酸リチウム粒子粉末を二次電池の正極として用いた場合に二次電池としてのサイクル特性が低下する傾向がある。好ましくはＮａ含有量が０．０２重量％以下であり、Ｓ含有量が０．００８重量％以下である
【００５０】
本発明１に係る四酸化三マンガン粒子粉末のＢＥＴ比表面積値は０．０４〜２．０ｍ２／ｇが好ましく、より好ましくは０．０５〜１．８ｍ２／ｇである。
【００５１】
本発明１に係る四酸化三マンガン粒子粉末の粒子形状は多面体状であり、三角状、四角状又は六角状の面を有する多面体である。
【００５２】
本発明１に係る四酸化三マンガン粒子粉末はＭｎ２Ｏ３を含んでいてもよい。
【００５３】
次に、本発明に係る四酸化三マンガン粒子粉末の製造法について述べる。
【００５４】
本発明に係る四酸化三マンガン粒子粉末は下記いずれかの製造法、または下記製造法を組み合わせて製造することができる。
【００５５】
即ち、マンガン塩水溶液とアルカリ水溶液とを反応させマンガン水酸化物を含有する水懸濁液とし、次いで、６０〜１００℃の温度範囲で酸化反応を行って四酸化三マンガン核粒子を得る一次反応を行い、該一次反応後の反応溶液にマンガン塩水溶液を添加した後、酸化反応を行って前記四酸化三マンガン核粒子の成長反応を行う二次反応によって四酸化三マンガン粒子を得る製造法において、一次反応のマンガン濃度を１．５ｍｏｌ／Ｌ以下にするとともに、二次反応のマンガン添加量を一次反応のマンガン濃度の等モル以下にする製造法（本発明２）、前記四酸化三マンガン粒子を得る製造法において、一次反応終了後の反応溶液を非酸化性雰囲気に切り替えた後、マンガン塩水溶液を添加し、次いで、３時間以内の熟成を行う製造法（本発明３）、前記四酸化三マンガン粒子を得る製造法において、一次反応及び／又は二次反応中にマンガンに対して０．５モル％以下の有機還元剤を存在させる製造法（本発明４）、前記四酸化三マンガン粒子を得る製造法において、過剰アルカリ濃度を１．０〜５ｍｏｌ／Ｌとして四酸化三マンガン粒子粉末を得る製造法（本発明５）である。
【００５６】
本発明においてはマンガン塩水溶液としては、硫酸マンガン水溶液、硝酸マンガン水溶液、蓚酸マンガン水溶液、酢酸マンガン水溶液等が挙げられ、これらは単独で又は必要に応じて２種以上組み合わせて用いてもよい。
【００５７】
本発明におけるアルカリ水溶液としては、水酸化ナトリウム水溶液、水酸化カリウム水溶液、アンモニア等のアルカリ水溶液を使用することができる。
【００５８】
本発明２乃至６の四酸化三マンガン粒子粉末の製造法においては、四酸化三マンガン核粒子を得る一次反応と、該四酸化三マンガン核粒子を成長させる二次反応からなる。一次反応と二次反応とにすることによって、より一次粒子が大きくＮａ含有量の少ない四酸化三マンガン粒子粉末を得ることができる。
【００５９】
本発明において、一次反応のマンガン濃度が１．５ｍｏｌ／Ｌ以上の場合には、反応溶液の濃度が高くなり安定的に生産することが困難である。二次反応のマンガン濃度が一次反応のマンガン濃度の等モルを越える場合には、粒子サイズの粒度分布が広がり、また、Ｎａ含有量が増加するため好ましくない。
【００６０】
なお、必要により、二次反応の終了後、更に一次反応の等モル以下のマンガン塩を添加する三次反応を行ってもよい。
【００６１】
本発明において、一次反応の終了後、水懸濁液の雰囲気を非酸化性雰囲気に切り替えるのは、二次反応における反応を容易に安定化させるためである。
【００６２】
熟成は、中和反応後の懸濁液に対して、２０〜１００℃の温度範囲、好ましくは５０〜９５℃の温度範囲で行う。熟成を行うことによって粒子サイズの粒度分布の狭い四酸化三マンガン粒子が得られるとともに、Ｎａを含有した不純物相（バーネサイト）の発生を抑制することができるので、Ｎａ含有量の低い四酸化三マンガン粒子粉末を得ることができる。３時間を超える熟成は、反応時間の増加につながり好ましくない。より好ましくは１〜３時間である。
【００６３】
本発明においては、有機還元剤を添加することが好ましい。有機還元剤としては、アスコルビン酸、ラクトース、ホルマリン等であり、アスコルビン酸が好ましい。有機還元剤の添加量はマンガンに対してモル比で０．５モル％以下が好ましい。０．５モル％を越える場合には、異相が発生し、粒子サイズが小さくなる傾向がある。
【００６４】
前記有機還元剤の添加時期は、マンガン塩水溶液、アルカリ水溶液、中和反応中、熟成中、酸化反応中等、特に限定されないが、好ましくはマンガン塩水溶液にあらかじめ添加しておくことが好ましい。
【００６５】
本発明においてはマンガンの当量よりも過剰量のアルカリ水溶液を添加することによって、粒子サイズの大きな四酸化三マンガンを容易に得ることができる。殊に、過剰のアルカリ量は１．０〜５．０ｍｏｌ／ｌが好ましく、１．０ｍｏｌ／ｌ未満の場合には、所望の粒子サイズを有する四酸化三マンガン粒子粉末を容易に得ることが困難となる。５．０ｍｏｌ／ｌの添加によって所望の粒子サイズ有する四酸化三マンガン粒子粉末を得ることができるので、必要以上に過剰にする意味はない。好ましくは１．５〜４．０ｍｏｌ／ｌである。
【００６６】
酸化反応は、反応溶液に酸化性ガスを通気するか、或いは、酸化剤を添加することによって行うことができ、例えば空気の通気が好ましい。
【００６７】
酸化反応の温度は６０〜９０℃が好ましい。
【００６８】
二次反応の終了後、水洗、乾燥を行って四酸化三マンガン粒子粉末とする。
【００６９】
次に、本発明に係る非水電解質二次電池用正極活物質（以下、単に「正極活物質」と言う。）について述べる。
【００７０】
本発明に係る正極活物質は、平均一次粒子径が３．０〜１５μｍである。平均一次粒子径が３．０μｍ未満の場合には、二次電池の正極を製造する際に充填密度が低くなり、また、バインダー量を増加させる必要があるなど、二次電池のエネルギー密度の低下を招く。一方、１５μｍを超える場合には、電流密度を増加させた場合にＬｉの脱挿入反応が低下する傾向がある。好ましくは３．０〜１２μｍである。
【００７１】
本発明に係る正極活物質は、Ｎａ含有量が０．０３重量％以下、Ｓ含有量が０．０１重量％以下である。Ｎａ含有量及びＳ含有量が前記範囲を超える場合は、二次電池としてのサイクル特性が低下する傾向がある。好ましくはＮａ含有量が０．０２５％以下、Ｓ含有量が０．００８重量％以下である。
【００７２】
本発明に係る正極活物質の粒子形状は等方的多面体である。鋭角部を有する粒子形状の場合には、導電材との接触が不均一となり好ましくない。
【００７３】
本発明に係る正極活物質はＬｉ１＋ｘＭｎ２−ｘＯ４の組成式で表されるマンガン酸リチウム粒子粉末であり、Ｌｉ／Ｍｎはモル比で０．５２〜０．６７であることが好ましい。０．５２未満の場合には、充放電容量は高いがＪａｈｎ−Ｔｅｌｌｅｒ効果による歪みの発生のためサイクル特性が低下する。また、０．６７を越える場合には、初期放電容量が十分ではないため好ましくない。前記組成式において、原子番号が１１以上の金属元素又は遷移金属元素をＭｎに対するモル比で０〜２０％含有してもよい。
【００７４】
なお、充放電容量及びサイクル特性に寄与しないＭｎ２Ｏ３、Ｍｎ３Ｏ４、ＭｎＯ２、Ｌｉ２ＭｎＯ３等の異相を含んでいても良い。
【００７５】
本発明に係る正極活物質のＢＥＴ比表面積値は、０．０４〜１．５ｍ２／ｇが好ましい。０．０４ｍ２／ｇ未満の場合には、電流密度を増加させた場合にＬｉの脱挿入反応が低下すると考えられ電池特性が低下する。１．５ｍ２／ｇを超える場合には、正極活物質の充填密度が低下することや電解液との反応性が過剰となり安全性が低下する。より好ましくは０．０６〜１．２ｍ２／ｇである。
【００７６】
本発明に係る正極活物質は、一次粒子が単独で挙動することができるため、平均一次粒子径と平均二次粒子径はほぼ同程度であり、平均二次粒子径は３．０〜１８μｍが好ましい。平均二次粒子径が３．０μｍ未満の場合には、二次電池の正極を製造する際に充填密度が低くなり、また、バインダー量を増加させる必要があるなど、二次電池のエネルギー密度の低下を招く。一方、１５μｍを超える場合には、電流密度を増加させた場合にＬｉの脱挿入反応が低下する傾向がある。好ましくは３．０〜１５μｍである。
【００７７】
本発明に係る正極活物質のタップ密度は２．０ｇ／ｍｌ以上が好ましい。その上限値は３．０ｇ／ｍｌ程度である。
【００７８】
次に、本発明に係る正極活物質の製造法について述べる。
【００７９】
リチウム原料としては炭酸リチウム、水酸化リチウム、硝酸リチウム、塩化リチウムなどが使用出来るが、炭酸リチウムが好ましい。
【００８０】
四酸化三マンガン粒子粉末とリチウム原料との混合割合は、モル比でＬｉ／Ｍｎ＝０．５２〜０．６７程度とするのが好ましい。０．５２以下の場合には容量は高いがＪａｈｎ−Ｔｅｌｌｅｒ効果による歪みの発生のため充放電サイクル特性が低下する。また、０．６７を越える場合には初期容量が十分ではない。
【００８１】
四酸化三マンガン粒子粉末とリチウム原料は均一な混合状態とする必要がある。均一に混合されていないと、部分的に組成比のズレが生じ容量及び可逆性の異なるマンガン酸リチウムが合成されることになり、また、マンガン酸リチウム以外の異相の発生原因にもなる。
【００８２】
混合物の焼成温度は５００〜１０００℃である。５００℃未満の場合には、高い結晶性を有するマンガン酸リチウム粒子粉末を得ることができない。１０００℃以上では単一相を得ることが困難となり電池特性に影響がでる。
【００８３】
焼成雰囲気は、酸素含有ガス、例えば空気中でよい。焼成時間は反応が均一に進行するように選択すればよいが、１〜４８時間が好ましく、より好ましくは１０〜２４時間である。
【００８４】
焼成後、粉砕してマンガン酸リチウム粒子粉末を得る。
【００８５】
次に、本発明に係る非水電解質二次電池について述べる。
【００８６】
本発明に係るマンガン酸リチウム粒子粉末を非水電解液二次電池用の正極活物質として用いて正極材を製造する場合には、アセチレンブラック、カーボンブラック等の導電剤及びポリテトラフルオロエチレン、ポリフッ化ビニリデン等の結着材などと混合して、所定の形状に成形して正極材とする。
【００８７】
また、負極活物質は特に制限されないが、例えば、リチウム金属、リチウム合金、リチウムを吸蔵放出可能な物質を用いることができ、例えば、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が挙げられる。
【００８８】
また、電解質も特に制限されないが、例えば、炭酸プロピレン、炭酸ジエチル、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種類の有機溶媒中に、過塩素酸リチウム、四フッ化ホウ酸リチウム、六フッ化リン酸リチウム等のリチウム塩の少なくとも１種を溶解したものを用いることができる。
【００８９】
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６０〜１３５ｍＡｈ／ｇ、６０℃での１００サイクル後の容量維持率が９０％以上である。
【００９０】
【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。
【００９１】
粒子粉末の粒子径は下記２種類の方法で測定した。
【００９２】
各粒子粉末の平均一次粒子径は、走査型電子顕微鏡（日立製作所製）で測定した。走査型電子顕微鏡写真の対角線上に存在する粒子から任意に一次粒子を１０個選び、粒子径を測定して、その平均値を平均一次粒子径とした。走査型電子顕微鏡写真は対角線上に２０〜４０個の粒子が存在する倍率が粒子径を測定精度の点から好ましい。
【００９３】
粒子粉末の平均二次粒子径は、レーザー散乱・回折方式「ＮＩＫＫＩＳＯ ＭＩＣＲＯＴＲＡＣ ＨＲＡ、ＭＯＤＥＬ９３２０−Ｘ１００：日機装社製」を用いて各粒子粉末の体積換算の粒度分布から二次粒子のＤ５０を測定して、平均二次粒子径とした。
【００９４】
正極活物質の同定、結晶構造及び結晶子サイズは、Ｘ線回折（ＲＩＧＡＫＵ Ｃｕ−Ｋα ４０ｋＶ ４０ｍＡ）により調べた。
【００９５】
また、粒子の形態については走査型電子顕微鏡（日立製作所製）により観察した。
【００９６】
ＢＥＴ比表面積はＢＥＴ法により測定した。
【００９７】
タップ密度は、「ＳＥＩＳＨＩＮ ＴＡＰＤＥＮＳＥＲ ＫＹＴ−３０００：（株）セイシン企業製」を用いて測定した。
【００９８】
＜正極の作製＞
マンガン酸リチウム粒子粉末と導電剤であるアセチレンブラックと結着材であるポリフッ化ビニリデンとを重量比８５：１０：５の割合で混合し、Ｎ−メチル−２−ピロリドンを加えペースト化し、該ペーストをアルミニウム箔に０．１５ｍｍ厚で塗布し、乾燥後、直径１６ｍｍの円盤に打ち抜いて正極を作製した。
【００９９】
負極にはリチウム箔を用い、これを１６ｍｍの円盤状に打ち抜いた。
【０１００】
＜二次電池の作製＞
セパレータはポリエチレン製からなり、これを１９ｍｍの円盤状に打ち抜いた。電解液にはＬｉＰＦ６を支持塩とするエチレンカーボネート（ＥＣ）とジエチルカーボネート（ＤＥＣ）を体積比１：１で混合したものを用いた。そして、アルゴン雰囲気のグローブボックス中でコイン型セル電池を作製した。
【０１０１】
二次電池の充放電サイクル試験は、前記コイン型電池セルを用いて、正極に対する電流密度を０．５ｍＡ／ｃｍ２とし、カットオフ電圧が４．５Ｖから３．０Ｖの間、６０℃の温度下で充放電を１００サイクル繰り返した後、放電容量を測定して初期放電容量に対する割合を求めた。
【０１０２】
＜四酸化三マンガン粒子粉末の製造：（本発明２による製造）＞
窒素通気のもと、１８．２ｍｏｌ／ｌの水酸化ナトリウム水溶液１５７．８ｌに２．０ｍｏｌ／ｌの硫酸マンガン水溶液２７７．９ｌを加えて全量を７００Ｌとし、中和反応を行って水酸化マンガン粒子を含有する水懸濁液を得た。このときのマンガン濃度は０．８ｍｏｌ／Ｌであり、過剰アルカリ濃度は２．５ｍｏｌ／ｌであった。得られた水酸化マンガン粒子を含む水懸濁液を窒素通気下、９０℃まで昇温し、次いで、空気を通気させ９０℃で酸化反応を行った。次いで、二次反応として０．４ｍｏｌ／ｌの硫酸マンガン水溶液１３８．９ｌを加えた後、空気を通気させ６０℃で酸化反応を行い、水洗、乾燥後、酸化マンガン粒子粉末を得た。二次反応のマンガン塩添加量は、一次反応のマンガン濃度に対して半分であった。
【０１０３】
得られた四酸化三マンガン粒子粉末はＭｎ３Ｏ４であり、平均一次粒子径９．０μｍ、ＢＥＴ比表面積値０．４ｍ２／ｇであった。Ｎａ含有量は０．０１重量％、Ｓ含有量は０．００１重量％であった。得られた四酸化三マンガン粒子粉末の走査型電子顕微鏡写真の観察結果を図１に示す。同図に示す通り、その粒子形状は三角状又は四角状の面をもつ多面体又は八面体であった。
【０１０４】
＜マンガン酸リチウム粒子粉末の製造＞
ここに得た四酸化三マンガン粒子粉末と炭酸リチウムとをＬｉ／Ｍｎが０．６２の割合になるように３０分混合し、均一な混合物を得た。得られた混合物をアルミナサヤに入れ、８４５℃、空気雰囲気で６時間保持してマンガン酸リチウム粒子粉末を得た。
【０１０５】
得られたマンガン酸リチウム粒子粉末は平均一次粒子径９．０μｍであって平均二次粒子径（Ｄ５０）１１．９μｍであって、Ｎａ含有量は０．０１９％、Ｓ含有量は０．００１％であった。ＢＥＴ比表面積値が０．３ｍ２／ｇ、タップ密度が２．３ｇ／ｍｌであった。得られたマンガン酸リチウム粒子粉末の走査型電子顕微鏡写真の観察結果を図２に示す。同図に示す通り、その粒子形状は鋭角部を有していない等方的多面体であった。
【０１０６】
ここで得たマンガン酸リチウム粒子粉末からなる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９１ｍＡｈ／ｇ、６０℃での１００サイクル後の容量維持率が９８％／１００ｃｙｃｌｅであった。
【０１０７】
【作用】
本発明において最も重要な点は、本発明に係る四酸化三マンガン粒子粉末、マンガン酸リチウムは、大きな一次粒子径を有し、しかも、凝集せず分散性に優れているという点である。
【０１０８】
本発明においては、理由は明らかではないが、一次反応と二次反応とに分けたことによって、不純物相であるＮａ−Ｍｎ系化合物の析出を抑制でき、更に、有機系還元剤を用いたこと、熟成工程を設けたこと、又は、高アルカリ領域で酸化反応を行ったことによって、一次粒子サイズが大きく粒度分布が均一で粒子の凝集が少なく、しかも、Ｎａ、Ｓ含有量の少ない四酸化三マンガン粒子を得ることができる。
【０１０９】
マンガン酸リチウム粒子の粒子径は前駆体になる四酸化三マンガン粒子の粒子径に大きく依存するので、前記四酸化三マンガン粒子を用いることによって、マンガン酸リチウム粒子粉末からなる正極活物質も大きな一次粒子となり、凝集粒子が少なく、粒度分布も優れ、Ｎａ、Ｓ含有量も低減できる。
【０１１０】
本発明に係る正極活物質を用いた二次電池の充放電サイクル特性が優れているのは、正極活物質の比表面積が小さく、また、等方的多面体であり鋭角部を有さない粒子形状であるため電解液との反応性が押さえられ、塗料化時の分散性及び充填性に優れることによるものと推定している。
【０１１１】
【実施例】
次に、実施例及び比較例を示す。
【０１１２】
実施例１〜４、比較例１〜４
一次反応及び二次反応のマンガン塩濃度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四酸化三マンガンを得た。
【０１１３】
このときの製造条件及び得られた四酸化三マンガン粒子粉末の諸特性を表１に示す。
【０１１４】
【表１】
実施例５：（本発明３による製造）
窒素通気のもと、１８．２ｍｏｌ／ｌの水酸化ナトリウム水溶液１５７．８ｌに２．０ｍｏｌ／ｌの硫酸マンガン水溶液２７７．９ｌを加えて全量を７００Ｌとし、中和反応を行って水酸化マンガン粒子を含有する水懸濁液を得た。このときのマンガン濃度は０．８ｍｏｌ／Ｌであり、過剰アルカリ濃度は２．５ｍｏｌ／ｌであった。得られた水酸化マンガン粒子を含む水懸濁液を窒素通気下、９０℃まで昇温させ、次いで空気を通気させ９０℃で酸化反応を行った。その後、窒素通気下で１時間熟成させた。次いで、二次反応として０．４ｍｏｌ／ｌの硫酸マンガン水溶液１３８．９ｌを加えた後、空気を通気させ６０℃で酸化反応を行い、水洗、乾燥後、酸化マンガン粒子粉末を得た。
【０１１６】
得られた四酸化三マンガン粒子粉末はＭｎ３Ｏ４であり、平均一次粒子径９．０μｍ、ＢＥＴ比表面積値０．３ｍ２／ｇであった。Ｎａ含有量は０．００５重量％、Ｓ含有量は０．００１重量％であった。得られた四酸化三マンガン粒子粉末の走査型電子顕微鏡写真の観察の結果、その粒子形状は八面体又は四角乃至六角状の面をもつ等方的多面体であった。
【０１１７】
実施例６〜７、比較例５、６
熟成時間を種々変化させた以外は前記実施例５と同様にして四酸化三マンガンを得た。
【０１１８】
このときの製造条件及び得られた四酸化三マンガン粒子粉末の諸特性を表２に示す。
【０１１９】
【表２】
実施例８：（本発明４による製造）
窒素通気のもと、１８．２ｍｏｌ／ｌの水酸化ナトリウム水溶液１５７．８ｌに２．０ｍｏｌ／ｌの硫酸マンガン水溶液２７７．９ｌ及びアスコルビン酸９８ｇを加えて全量を７００Ｌとし、中和反応を行って水酸化マンガン粒子を含有する水懸濁液を得た。このときのマンガン濃度は０．８ｍｏｌ／Ｌであり、過剰アルカリ濃度は２．５ｍｏｌ／ｌであり、アスコルビン酸の添加量はマンガンに対して０．００８ｍｏｌ％であった。得られた水酸化マンガン粒子を含む水懸濁液を窒素通気下、９０℃で１時間熟成させた。熟成後、空気を通気させ９０℃で酸化反応を行った。次いで、二次反応として０．４ｍｏｌ／ｌの硫酸マンガン水溶液１３８．９ｌを加えた後、空気を通気させ６０℃で酸化反応を行い、水洗、乾燥後、酸化マンガン粒子粉末を得た。
【０１２１】
得られた四酸化三マンガン粒子粉末はＭｎ３Ｏ４であり、平均一次粒子径９．０μｍ、ＢＥＴ比表面積が０．３ｍ２／ｇであった。Ｎａ含有量は０．００７重量％、Ｓ含有量は０．００１重量％であった。得られた四酸化三マンガン粒子粉末の走査型電子顕微鏡写真の観察の結果、その粒子形状は八面体、又は、四角状乃至六角状の面をもつ等方的多面体であった。
【０１２２】
実施例９〜１１、比較例７、８
マンガンに対するアスコルビン酸の量を種々変化させた以外は前記実施例８と同様にして四酸化三マンガン粒子粉末を得た。
【０１２３】
このときの製造条件及び得られた四酸化三マンガン粒子粉末の諸特性を表３に示す。
【０１２４】
【表３】
実施例１２：（本発明５による製造）
窒素通気のもと、１８．２ｍｏｌ／ｌの水酸化ナトリウム水溶液１０２．７ｌに２．０ｍｏｌ／ｌの硫酸マンガン水溶液２７７．９ｌを加えて全量を７００Ｌとし、中和反応を行って水酸化マンガン粒子を含有する水懸濁液を得た。このときのマンガン濃度は０．８ｍｏｌ／Ｌであり、過剰アルカリ濃度は１．５ｍｏｌ／ｌであった。得られた水酸化マンガン粒子を含む水懸濁液に空気を通気させ９０℃で酸化反応を行った。次いで、二次反応として０．４ｍｏｌ／ｌの硫酸マンガン水溶液１３８．９ｌを加えた後、空気を通気させ６０℃で酸化反応を行い、水洗、乾燥後、酸化マンガン粒子粉末を得た。
【０１２６】
得られた四酸化三マンガン粒子粉末はＭｎ３Ｏ４であり、平均一次粒子径６．０μｍ、ＢＥＴ比表面積が０．５ｍ２／ｇであった。Ｎａ含有量は０．００７重量％、Ｓ含有量は０．００１重量％であった。得られた四酸化三マンガン粒子粉末の走査型電子顕微鏡写真の観察の結果、その粒子形状は八面体、又は、四角状乃至六角状の面をもつ等方的多面体であった。
【０１２７】
実施例１３〜１５、比較例９〜１１
一次反応に対する過剰アルカリ量を種々変化させた以外は前記実施例１２と同様にして四酸化三マンガンを得た。
【０１２８】
このときの製造条件及び得られた四酸化三マンガン粒子粉末の諸特性を表４に示す。なお、比較例１１は電解二酸化マンガン（ＥＭＤ）である。
【０１２９】
【表４】
実施例１６：（本発明６による製造）
窒素通気のもと、１８．２ｍｏｌ／ｌの水酸化ナトリウム水溶液１５７．８ｌに２．０ｍｏｌ／ｌの硫酸マンガン水溶液２７７．９ｌ及びアスコルビン酸４９０ｇを加えて全量を７００Ｌとし、中和反応を行って水酸化マンガン粒子を含有する水懸濁液を得た。このときのマンガン濃度は０．８ｍｏｌ／Ｌであり、過剰アルカリ濃度は２．５ｍｏｌ／ｌ、アスコルビン酸の添加量はマンガンに対して０．０５ｍｏｌ％であった。得られた水酸化マンガン粒子を含む水懸濁液を窒素通気下、９０℃まで昇温させ、次いで空気を通気させ９０℃で酸化反応を行った。その後、窒素通気下で２時間熟成させた。次いで、二次反応として０．４ｍｏｌ／ｌの硫酸マンガン水溶液１３８．９ｌを加えた後、空気を通気させ６０℃で酸化反応を行い、水洗、乾燥後、酸化マンガン粒子粉末を得た。二次反応のマンガン塩添加量は、一次反応のマンガン濃度に対して半分であった。
【０１３１】
得られた四酸化三マンガン粒子粉末の諸特性を表５に示す。得られた四酸化三マンガン粒子粉末の走査型電子顕微鏡写真の観察の結果、その粒子形状は八面体、又は、四角状乃至六角状の面をもつ等方的多面体であった。
【０１３２】
実施例１７
反応条件を種々変化させた以外は前記実施例１６と同様にして四酸化三マンガンを得た。
【０１３３】
このときの製造条件及び得られた四酸化三マンガン粒子粉末の諸特性を表５に示す。
【０１３４】
【表５】
実施例１８〜３４、比較例１２〜２２
四酸化三マンガン粒子粉末の種類を種々変化させた以外は、前記発明の実施の形態の＜マンガン酸リチウム粒子粉末の製造＞と同様にしてマンガン酸リチウム粒子粉末を得た。
【０１３６】
このときの製造条件、マンガン酸リチウム粒子粉末の諸特性及び前記発明の実施の形態と同様にして行った電池評価の結果を表６に示す。
【０１３７】
実施例で得られたマンガン酸リチウム粒子粉末の粒子形状はいずれも、鋭角部のない等方的多面体であった。
【０１３８】
【表６】
【発明の効果】
本発明に係る四酸化三マンガン粒子粉末は、平均一次粒子径が大きく、Ｎａ含有量及びＳ含有量が少ないので、マンガン酸リチウム粒子粉末の前駆体として好適である。
【０１４０】
本発明に係る正極活物質は、平均一次粒子径が大きく、Ｎａ含有量及びＳ含有量が少なく、分散性及び充填性が優れているので、充放電サイクル特性に優れた非水電解液二次電池を提供することができる。
【０１４１】
本発明に係る二次電池は、前記正極活物質を用いることによって、理論値とほぼ同程度の初期放電容量を示し、しかも高温でのサイクル特性に優れているので、二次電池として好適である。
【図面の簡単な説明】
【図１】発明の実施の形態で得られた四酸化三マンガン粒子粉末の電子顕微鏡写真（３５００倍）を示す。
【図２】発明の実施の形態で得られたマンガン酸リチウム粒子粉末からなる正極活物質の電子顕微鏡写真（３５００倍）を示す。
【図３】比較例１１で用いた電解二酸化マンガンの電子顕微鏡写真（３５００倍）を示す。
【図４】比較例２２で得られたマンガン酸リチウム粒子粉末の電子顕微鏡写真（３５００倍）を示す。[0001]
[Industrial applications]
The present invention relates to lithium manganate particles having excellent charge / discharge cycle characteristics of a secondary battery as a positive electrode active material for a nonaqueous electrolyte secondary battery.
[0002]
[Prior art]
2. Description of the Related Art In recent years, portable and cordless electronic devices such as AV devices and personal computers have been rapidly advancing, and there is an increasing demand for small, lightweight, high-energy-density secondary batteries as drive power supplies for these devices. It is also expected to be used in vehicles such as electric vehicles, hybrid vehicles, and fuel cells, and in middle- and large-sized batteries for backup power sources. Under such circumstances, attention has been paid to a lithium ion secondary battery that has advantages of high charge / discharge voltage and large charge / discharge capacity.
[0003]
Conventionally, a positive electrode active material useful for a high energy type lithium ion secondary battery having a voltage of 4 V class is LiMn having a spinel structure. 2 O 4 , LiMnO with zigzag layered structure 2 , Rock salt type layered structure LiCoO 2 , LiCo 1-X Ni X O 2 , LiNiO 2 Are generally known, and among them, LiCoO 2 Is superior in that it has a high voltage and a high capacity, but the production cost is high due to the small supply of cobalt raw material, the environmental safety of waste batteries, and the thermal stability due to the unstable structure. The problem exists.
[0004]
Therefore, lithium manganate particles having a spinel structure and made from manganese, which has a large supply amount, is low in cost, has good environmental suitability, and is excellent in safety (basic composition: LiMn 2 O 4 -The same applies to the following-).
[0005]
As is well known, the lithium manganate particles can be obtained by mixing a manganese compound and a lithium compound at a predetermined ratio and baking the mixture in a temperature range of 500 to 1000 ° C.
[0006]
However, when lithium manganate particles are used as a positive electrode active material of a lithium ion secondary battery, there is a problem in that although they have a high voltage and a high energy density, they have poor charge / discharge cycle characteristics. This may be caused by the collapse of the structure due to the elution of Mn in the crystal structure during charge / discharge, and the deterioration of the structure due to the non-uniform composition of lithium manganate because its properties are determined by its composition.
[0007]
In a lithium ion secondary battery using lithium manganate particles, it is the most demanded at present to suppress deterioration of charge / discharge capacity due to repeated charge / discharge and to improve charge / discharge cycle characteristics.
[0008]
In order to improve the charge / discharge cycle characteristics, it is necessary that the positive electrode active material composed of the lithium manganate particles is excellent in filling properties and has an appropriate size. The methods include controlling the particle size and particle size distribution of lithium manganate particles, controlling the firing temperature to obtain high-crystalline lithium manganate particles, and strengthening the bonding strength of crystals by adding different elements. And a method of performing a surface treatment to suppress the elution of Mn.
[0009]
As methods for obtaining lithium manganate particles having an appropriate size, various methods described in Patent Documents 1 to 23 are known.
[0010]
[Patent Document 1]
JP-A-10-162826
[Patent Document 2]
JP-A-10-172567
[Patent Document 3]
JP-A-10-182159
[Patent Document 4]
JP-A-10-255797
[Patent Document 5]
JP-A-10-322227
[Patent Document 6]
JP-A-11-1323
[Patent Document 7]
JP-A-11-71115
[Patent Document 8]
JP-A-11-157841
[Patent Document 9]
JP-A-11-180717
[Patent Document 10]
JP-A-11-219705
[Patent Document 11]
JP-A-11-233112
[Patent Document 12]
JP-A-2000-12031
[Patent Document 13]
JP 2000-143247 A
[Patent Document 14]
JP-A-2000-215895
[Patent Document 15]
JP 2000-223118 A
[Patent Document 16]
JP-A-2000-281349
[Patent Document 17]
JP 2000-281351 A
[Patent Document 18]
JP 2001-26425 A
[Patent Document 19]
JP 2001-93527 A
[Patent Document 20]
JP 2001-114521 A
[Patent Document 21]
JP 2001-122626 A
[Patent Document 22]
JP 2001-240417 A
[Patent Document 23]
JP 2002-198047 A
[0011]
[Problems to be solved by the invention]
As a positive electrode active material for a nonaqueous electrolyte secondary battery, lithium manganate particles having excellent charge / discharge cycle characteristics of a secondary battery have not yet been obtained.
[0012]
That is, Patent Document 1 mentioned above discloses a production method for obtaining lithium manganate particles having excellent particle size distribution by spray pyrolysis, but the obtained lithium manganate particles are porous and have a specific surface area. As a result, it becomes difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. In addition, the packing density is hardly sufficient.
[0013]
Patent Document 2 discloses a production method in which a slurry of a manganese compound and a lithium compound is dried with a spray drier and then fired, but constitutes an aggregate composed of a large number of primary particles. In addition, since the specific surface area is increased, it is difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. In addition, the packing density is hardly sufficient.
[0014]
Patent Literature 3 mentioned above describes lithium manganate using trimanganese tetroxide containing 500 ppm of S as an example. However, it contains a large amount of S, and is charged with a secondary battery. It is hardly enough to improve the discharge cycle characteristics.
[0015]
Patent Document 4 discloses that manganese oxide and oxywater are plate-like particles having an average plate diameter of 1 to 50 μm, an average plate thickness of 0.2 to 2 μm, and a plate diameter / plate thickness ratio of 3 or more. Manganese oxide, a production method of obtaining a lithium manganese composite oxide having excellent cycle durability by mixing and heating manganese hydroxide and a lithium salt is disclosed, but the obtained lithium manganese composite oxide has a particle size of Since the specific surface area is small, it is difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. In addition, the packing density is hardly sufficient.
[0016]
Patent Literature 5 discloses a lithium manganate particle powder in which the average particle diameter of primary particles and secondary particles is specified. However, the primary particles are small, and the secondary particles are composed of a large number of primary particles. As a result, the specific surface area becomes large, and it becomes difficult to suppress the elution of Mn. As a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. In addition, the packing density is hardly sufficient.
[0017]
Patent Literature 6 mentioned above describes a lithium manganate particle powder in which the average particle diameter of primary particles and secondary particles is specified. However, since it is an aggregate and has a large specific surface area, the elution of Mn occurs. It becomes difficult to suppress this, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. Further, in the examples, lithium manganate particles having an average primary particle diameter of 2.0 μm and an average secondary particle diameter of 2.0 μm are described, but the average particle diameter is small and it is difficult to say that the filling property is sufficient. It is.
[0018]
Patent Literature 7 discloses lithium manganate particles having an average agglomerated particle diameter of 1 to 50 µm and an average primary particle diameter of 3.0 µm or less, which is obtained in Examples. Since the average primary particle diameter of the lithium manganate particles is as small as 1.0 μm or less and the specific surface area is large, it is difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate.
[0019]
Patent Document 8 mentioned above has a specific surface area of 0.3 to 0.7 m. 2 / G and SO 4 Lithium manganate particles having a content of 0.4% by weight or less are described. 2 As a raw material, the primary particles are small, and it is hard to say that the characteristics are sufficiently improved with the S content shown in the examples.
[0020]
Patent Literature 9 discloses lithium manganate particles having a cubic particle shape, a particle diameter of 0.01 to 10 μm, and a specific surface area in the range of 1 to 100 m2 / g. Since the particles have voids, the specific surface area is large, and since the particles are subjected to hydrothermal treatment, the primary particles are small and the improvement in characteristics is not sufficient.
[0021]
Further, Patent Literature 10 mentioned above discloses lithium manganate particles having a small content of fine particles having an average particle diameter of 1.0 μm or less, but primary particles are not considered. Electrolytic MnO 2 Is used, and the specific surface area with respect to the average particle diameter is large, it is estimated that the particles are aggregated particles, and it is difficult to suppress the elution of Mn. As a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. I do.
[0022]
Patent Document 11 mentioned above discloses that MnSO 4 Water is added to the hydrate to adjust the concentration of the aqueous solution, and after heating, hydrogen peroxide is added dropwise, ammonia water is added, and washing and drying are performed. Although it is disclosed that lithium manganate having improved charge / discharge characteristics can be obtained by heat treatment, it is difficult to suppress the elution of Mn because the primary particles are small and the specific surface area is large. Battery charge / discharge cycle characteristics are degraded. In addition, the packing density is hardly sufficient.
[0023]
Patent Literature 12 discloses lithium manganate particles having an average particle diameter of 1 to 45 μm, but does not consider primary particles, and the obtained lithium manganate particles are small primary particles. Are secondary particles that are agglomerated, so that the specific surface area is large and it is difficult to suppress the elution of Mn. As a result, the charge / discharge cycle characteristics of the secondary battery deteriorate.
[0024]
Patent Literature 13 discloses lithium manganate particles having a primary particle diameter of 0.5 to 2.0 μm. However, since the primary particles are small, the packing density is low, and the specific surface area is low. Therefore, it is difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate.
[0025]
Patent Document 14 discloses that the content of S is SO 4 Specific surface area 0.5 to 3m at 0.6% by weight or less in ion conversion 2 / G, a spinel-type lithium manganese oxide having an average particle diameter of 1 to 45 μm is disclosed. However, since CMD (chemically synthesized manganese dioxide) is used, the primary particles are small, and it is hard to say that the characteristics are sufficiently improved. .
[0026]
Patent Document 15 discloses that lithium carbonate having a size of 10 μm or more and 100 μm or less can be obtained by mixing and firing lithium carbonate and manganese dioxide. Therefore, it is difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. In addition, the packing density is hardly sufficient.
[0027]
Patent Documents 16 and 17 have a median diameter of 10 μm or less obtained by mixing and firing a lithium compound with manganese oxide having a median diameter of 10 μm or less obtained by heat-treating spherical manganese carbonate in a nitrogen atmosphere. Tap density 1.8 g / cm 3 Although it is disclosed that a lithium manganese oxide as described above can be obtained, since manganese carbonate is used as a raw material, it is difficult to suppress the elution of Mn because the primary particles are small and the specific surface area is large, and as a result, In addition, the charge / discharge cycle characteristics of the secondary battery deteriorate.
[0028]
Patent Document 18 discloses that lithium manganate having good battery characteristics can be obtained by mixing and firing electrolytic manganese dioxide having a reduced Na content and having an average particle size of 3 to 20 μm with a lithium raw material. However, since electrolytic manganese dioxide is used as a raw material, the value of the specific surface area with respect to the average particle diameter is large, and it is difficult to suppress the elution of Mn. As a result, the charge / discharge cycle characteristics of the secondary battery are reduced. descend.
[0029]
Further, in the above-mentioned Patent Document 19, manganese hydroxide is precipitated after forming a manganese complex salt, oxidized in a stream of air at 40 to 400 ° C., mixed with a lithium compound after obtaining trimanganese tetroxide, and calcined. Although a positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the above is disclosed, it is difficult to say that the primary particles are small and the characteristics are not sufficiently improved.
[0030]
Patent Document 20 discloses that a manganese ion is reacted with a complexing agent to form a manganese complex salt, which is then reacted with an alkali metal hydroxide to produce manganese hydroxide, and then reacted with an oxidizing agent to form tetroxide. Although it is disclosed that trimanganese is obtained, it is difficult to say that the primary particles are small enough to improve the characteristics.
[0031]
Patent Literature 21 discloses a lithium manganate particle powder having a specified particle size distribution, but does not consider primary particles, and uses electrolytic manganese dioxide (EMD) or CMD as a manganese raw material. And the specific surface area with respect to the average particle diameter is large, it is presumed that the particles are aggregated particles, and it is difficult to suppress the elution of Mn. As a result, the charge / discharge cycle characteristics are reduced.
[0032]
Further, in the above-mentioned Patent Document 22, a manganese oxide seed is obtained in a solution, manganese oxide and a basic compound are reacted, oxidized to grow particles, and then reacted with a lithium compound or subjected to proton substitution. Although a method for producing lithium manganate having excellent crystallinity and a large particle size and a uniform particle size distribution is disclosed, a step of adding manganese sulfate and sodium hydroxide in the example and growing a manganese oxide seed is included. As described, the reaction was completed at pH 6.4, and in this region, the S component was adsorbed and the amount of remaining S was estimated to be high, and the value of the specific surface area with respect to the particle size was large. It becomes difficult to suppress the elution of Mn, and as a result, the charge / discharge cycle characteristics of the secondary battery deteriorate. In addition, the packing density is hardly sufficient.
[0033]
Patent Literature 23 discloses a lithium secondary battery characterized in that the sulfur content in the lithium manganese composite oxide is 2% or less and a method for producing the same. A positive electrode is produced using electrolytic manganese dioxide in an amount of 1 to 2%, which is not sufficient for improving characteristics.
[0034]
Therefore, an object of the present invention is to provide a lithium manganate particle powder having excellent charge / discharge cycle characteristics of a secondary battery as a positive electrode active material for a nonaqueous electrolyte secondary battery.
[0035]
[Means for Solving the Problems]
The technical problem can be achieved by the present invention as described below.
[0036]
That is, according to the present invention, the average primary particles are 3.0 to 15 μm, the Na content is 0.02% by weight or less, the S content is 0.01% by weight or less, and the particle shape is triangular or square. Trimanganese tetroxide particles which are polyhedrons having a hexagonal or hexagonal surface (Invention 1).
[0037]
The present invention also provides a manganese hydroxide-containing aqueous suspension obtained by neutralizing an aqueous manganese salt solution with an alkaline aqueous solution, and then performing an oxidation reaction in a temperature range of 60 to 100 ° C. to form a trimanganese tetroxide nucleus. A primary reaction for obtaining particles, a manganese salt aqueous solution is added to the reaction solution after the primary reaction, and an oxidation reaction is performed to perform a growth reaction of the trimanganese tetroxide core particles. Wherein the manganese concentration in the primary reaction is 1.5 mol / L or less and the amount of manganese added in the secondary reaction is equal to or less than the manganese concentration in the primary reaction. This is a method for producing manganese particles (Invention 2).
[0038]
The present invention also provides a manganese hydroxide-containing aqueous suspension obtained by neutralizing an aqueous manganese salt solution with an alkaline aqueous solution, and then performing an oxidation reaction in a temperature range of 60 to 100 ° C. to form a trimanganese tetroxide nucleus. A primary reaction for obtaining particles, a manganese salt aqueous solution is added to the reaction solution after the primary reaction, and an oxidation reaction is performed to perform a growth reaction of the trimanganese tetroxide core particles. Wherein the reaction solution after the completion of the primary reaction is switched to a non-oxidizing atmosphere, an aqueous manganese salt solution is added, and then aging is performed within 3 hours. This is a method for producing a powder (the present invention 3).
[0039]
The present invention also provides a manganese hydroxide-containing aqueous suspension obtained by neutralizing an aqueous manganese salt solution with an alkaline aqueous solution, and then performing an oxidation reaction in a temperature range of 60 to 100 ° C. to form a trimanganese tetroxide nucleus. A primary reaction for obtaining particles, a manganese salt aqueous solution is added to the reaction solution after the primary reaction, and an oxidation reaction is performed to perform a growth reaction of the trimanganese tetroxide core particles. Wherein the organic reducing agent is present in an amount of 0.5 mol% or less with respect to manganese during the reaction (the present invention 4).
[0040]
The present invention also provides a manganese hydroxide-containing aqueous suspension obtained by neutralizing an aqueous manganese salt solution with an alkaline aqueous solution, and then performing an oxidation reaction in a temperature range of 60 to 100 ° C. to form a trimanganese tetroxide nucleus. A primary reaction for obtaining particles, a manganese salt aqueous solution is added to the reaction solution after the primary reaction, and an oxidation reaction is performed to perform a growth reaction of the trimanganese tetroxide core particles. Wherein the excess alkali concentration is set to 1.0 to 5.0 mol / L (the present invention 5).
[0041]
The present invention also provides a manganese hydroxide-containing aqueous suspension obtained by neutralizing an aqueous manganese salt solution with an alkaline aqueous solution, and then performing an oxidation reaction in a temperature range of 60 to 100 ° C. to form a trimanganese tetroxide nucleus. A primary reaction for obtaining particles is performed, and after the completion of the primary reaction, an aqueous solution of a manganese salt in an equimolar amount or less with respect to manganese used in the primary reaction is added to the reaction solution after switching to a non-oxidizing atmosphere, and aging within 3 hours. After performing the oxidation reaction, the manganese concentration in the primary reaction is reduced to 1.5 mol / L or less in a production method of obtaining trimanganese tetroxide particles by a secondary reaction in which a growth reaction of the trimanganese tetroxide core particles is performed by performing an oxidation reaction. Wherein the organic reducing agent is present in an amount of 0.5 mol% or less based on manganese during the reaction, and the excess alkali concentration is adjusted to 1.0 to 5 mol / L. A method for producing particles (Invention 6).
[0042]
The present invention also provides an isotropic polyhedron having an average primary particle diameter of 3.0 to 15 μm, an Na content of 0.03% by weight or less, an S content of 0.01% by weight or less, and a particle shape of isotropic. The present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a lithium manganate particle powder of the present invention (Invention 7).
[0043]
The method according to claim 8, wherein the trimanganese tetroxide particles and the lithium compound are mixed and heat-treated at 500C to 1000C. A method (Invention 8).
[0044]
Further, the present invention is a non-aqueous electrolyte secondary battery using the positive electrode active material for a non-aqueous electrolyte secondary battery (Invention 9).
[0045]
Next, the configuration of the present invention will be described in more detail.
[0046]
First, the trimanganese tetroxide particles according to the present invention 1 will be described.
[0047]
In the present invention, the “primary particles” represent the smallest particles that can exist alone.
[0048]
The trimanganese tetroxide particle powder according to the first aspect of the present invention has an average primary particle diameter of 3.0 to 15 μm. When the average primary particle diameter is less than 3.0 μm, the packing density becomes low when the lithium manganate particles obtained using the trimanganese tetroxide particles are manufactured as a positive electrode of a secondary battery, and the energy density becomes low. Decreases. When the average primary particle size is 15 μm or more, when the lithium manganate particles obtained using the trimanganese tetroxide particles are used as a positive electrode of a secondary battery and the current density is increased, Li Deinsertion reactions tend to decrease. Preferably it is 3.0 to 12 μm.
[0049]
The trimanganese tetroxide particles according to the first aspect of the present invention have a Na content of 0.03% by weight or less and an S content of 0.01% by weight or less. When the Na content and the S content exceed the above ranges, when the lithium manganate particles obtained by using the trimanganese tetroxide particles are used as a positive electrode of a secondary battery, the cycle characteristics as a secondary battery are obtained. Tends to decrease. Preferably, the Na content is 0.02% by weight or less, and the S content is 0.008% by weight or less.
[0050]
The BET specific surface area of the trimanganese tetroxide particles according to the present invention 1 is 0.04 to 2.0 m. 2 / G is preferable, and more preferably 0.05 to 1.8 m 2 / G.
[0051]
The particle shape of the trimanganese tetroxide particles according to the first aspect of the present invention is a polyhedron having a triangular, quadrangular or hexagonal surface.
[0052]
Trimanganese tetroxide particles according to the first aspect of the present invention contain Mn. 2 O 3 May be included.
[0053]
Next, a method for producing trimanganese tetroxide particles according to the present invention will be described.
[0054]
The trimanganese tetroxide particles according to the present invention can be produced by any of the following production methods or a combination of the following production methods.
[0055]
That is, a manganese salt aqueous solution is reacted with an alkali aqueous solution to form a water suspension containing manganese hydroxide, and then an oxidation reaction is performed at a temperature in the range of 60 to 100 ° C. to obtain primary manganese tetroxide core particles. After adding a manganese salt aqueous solution to the reaction solution after the primary reaction, a secondary reaction of performing an oxidation reaction to perform a growth reaction of the trimanganese tetroxide core particles to obtain trimanganese tetroxide particles by a secondary reaction. A production method (the present invention 2) in which the manganese concentration in the primary reaction is 1.5 mol / L or less and the amount of manganese added in the secondary reaction is equal to or less than the molar amount of manganese in the primary reaction (the present invention 2); In the production method, the reaction solution after the completion of the primary reaction is switched to a non-oxidizing atmosphere, an aqueous solution of manganese salt is added, and then ripening is performed within 3 hours ( Invention 3), a method for producing trimanganese tetroxide particles, wherein an organic reducing agent is present in an amount of 0.5 mol% or less based on manganese during the primary reaction and / or the secondary reaction (Invention 4). A method for producing trimanganese tetroxide particles by setting the excess alkali concentration to 1.0 to 5 mol / L in the method for producing trimanganese tetroxide particles (the present invention 5).
[0056]
In the present invention, examples of the manganese salt aqueous solution include a manganese sulfate aqueous solution, a manganese nitrate aqueous solution, a manganese oxalate aqueous solution, a manganese acetate aqueous solution, and the like, and these may be used alone or in combination of two or more as needed.
[0057]
As the aqueous alkali solution in the present invention, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, or an aqueous alkali solution such as ammonia can be used.
[0058]
The method for producing trimanganese tetroxide particles of the present invention 2 to 6 comprises a primary reaction for obtaining trimanganese tetroxide core particles and a secondary reaction for growing the trimanganese tetroxide core particles. By performing the primary reaction and the secondary reaction, trimanganese tetroxide particles having larger primary particles and less Na content can be obtained.
[0059]
In the present invention, when the manganese concentration in the primary reaction is 1.5 mol / L or more, the concentration of the reaction solution becomes high, and it is difficult to stably produce. If the manganese concentration of the secondary reaction exceeds the equimolar concentration of the manganese concentration of the primary reaction, the particle size distribution of the particle size broadens and the Na content increases, which is not preferable.
[0060]
If necessary, after the completion of the secondary reaction, a tertiary reaction in which an equimolar or less manganese salt of the primary reaction is further added may be performed.
[0061]
In the present invention, the reason for switching the atmosphere of the aqueous suspension to the non-oxidizing atmosphere after the completion of the primary reaction is to stabilize the reaction in the secondary reaction easily.
[0062]
The aging is performed on the suspension after the neutralization reaction in a temperature range of 20 to 100 ° C, preferably 50 to 95 ° C. By performing aging, trimanganese tetroxide particles having a narrow particle size distribution of the particle size can be obtained and the generation of an impurity phase (burnesite) containing Na can be suppressed. Particle powder can be obtained. Aging for more than 3 hours is not preferable because it leads to an increase in the reaction time. More preferably, it is 1 to 3 hours.
[0063]
In the present invention, it is preferable to add an organic reducing agent. Examples of the organic reducing agent include ascorbic acid, lactose, and formalin, and ascorbic acid is preferable. The amount of the organic reducing agent to be added is preferably not more than 0.5% by mole relative to manganese. When the content exceeds 0.5 mol%, a hetero phase is generated and the particle size tends to be reduced.
[0064]
The timing of adding the organic reducing agent is not particularly limited, such as an aqueous manganese salt solution, an aqueous alkaline solution, during a neutralization reaction, during aging, or during an oxidation reaction, but it is preferable to add the organic reducing agent to the aqueous manganese salt solution in advance.
[0065]
In the present invention, trimanganese tetroxide having a large particle size can be easily obtained by adding an aqueous alkali solution in excess of the equivalent of manganese. In particular, the amount of excess alkali is preferably 1.0 to 5.0 mol / l, and if it is less than 1.0 mol / l, it is difficult to easily obtain trimanganese tetroxide particles having a desired particle size. It becomes. By adding 5.0 mol / l, trimanganese tetroxide particles having a desired particle size can be obtained. Preferably, it is 1.5 to 4.0 mol / l.
[0066]
The oxidation reaction can be carried out by passing an oxidizing gas through the reaction solution or by adding an oxidizing agent. For example, air ventilation is preferable.
[0067]
The temperature of the oxidation reaction is preferably from 60 to 90C.
[0068]
After completion of the secondary reaction, washing and drying are performed to obtain trimanganese tetroxide particles.
[0069]
Next, the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention (hereinafter, simply referred to as “positive electrode active material”) will be described.
[0070]
The positive electrode active material according to the present invention has an average primary particle diameter of 3.0 to 15 μm. When the average primary particle diameter is less than 3.0 μm, the packing density becomes low when manufacturing the positive electrode of the secondary battery, and the energy density of the secondary battery decreases, for example, the binder amount needs to be increased. Invite. On the other hand, if it exceeds 15 μm, the Li insertion / removal reaction tends to decrease when the current density is increased. Preferably it is 3.0 to 12 μm.
[0071]
The positive electrode active material according to the present invention has a Na content of 0.03% by weight or less and an S content of 0.01% by weight or less. When the Na content and the S content exceed the above ranges, the cycle characteristics of the secondary battery tend to decrease. Preferably, the Na content is 0.025% or less and the S content is 0.008% by weight or less.
[0072]
The particle shape of the positive electrode active material according to the present invention is an isotropic polyhedron. In the case of a particle shape having an acute angle portion, the contact with the conductive material is not uniform, which is not preferable.
[0073]
The positive electrode active material according to the present invention is Li 1 + x Mn 2-x O 4 It is preferable that Li / Mn is 0.52 to 0.67 in molar ratio. If it is less than 0.52, the charge / discharge capacity is high, but the cycle characteristics deteriorate due to the occurrence of distortion due to the Jahn-Teller effect. On the other hand, if it exceeds 0.67, the initial discharge capacity is not sufficient, which is not preferable. In the above composition formula, a metal element or a transition metal element having an atomic number of 11 or more may be contained in a molar ratio of 0 to 20% with respect to Mn.
[0074]
In addition, Mn which does not contribute to charge / discharge capacity and cycle characteristics 2 O 3 , Mn 3 O 4 , MnO 2, Li 2 MnO 3 Etc. may be included.
[0075]
The BET specific surface area of the positive electrode active material according to the present invention is 0.04 to 1.5 m. 2 / G is preferred. 0.04m 2 If it is less than / g, it is considered that the Li insertion / removal reaction is reduced when the current density is increased, and the battery characteristics are reduced. 1.5m 2 If it exceeds / g, the packing density of the positive electrode active material decreases and the reactivity with the electrolytic solution becomes excessive, resulting in a decrease in safety. More preferably 0.06 to 1.2 m 2 / G.
[0076]
In the positive electrode active material according to the present invention, since the primary particles can behave independently, the average primary particle size and the average secondary particle size are substantially the same, and the average secondary particle size is 3.0 to 18 μm. preferable. When the average secondary particle diameter is less than 3.0 μm, the packing density becomes low when manufacturing the positive electrode of the secondary battery, and the energy density of the secondary battery needs to be increased. Causes a decline. On the other hand, if it exceeds 15 μm, the Li insertion / removal reaction tends to decrease when the current density is increased. Preferably it is 3.0 to 15 μm.
[0077]
The tap density of the positive electrode active material according to the present invention is preferably 2.0 g / ml or more. Its upper limit is about 3.0 g / ml.
[0078]
Next, a method for producing the positive electrode active material according to the present invention will be described.
[0079]
As a lithium raw material, lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride and the like can be used, but lithium carbonate is preferable.
[0080]
The mixing ratio of the trimanganese tetroxide particles and the lithium raw material is preferably about Li / Mn = 0.52 to 0.67 in molar ratio. When it is 0.52 or less, the capacity is high, but the charge / discharge cycle characteristics are deteriorated due to the occurrence of distortion due to the Jahn-Teller effect. If it exceeds 0.67, the initial capacity is not sufficient.
[0081]
The trimanganese tetroxide particles and the lithium raw material need to be in a uniform mixed state. If they are not mixed uniformly, the composition ratio will be partially deviated, and lithium manganate having different capacity and reversibility will be synthesized, and it will also cause a different phase other than lithium manganate.
[0082]
The firing temperature of the mixture is 500-1000 ° C. When the temperature is lower than 500 ° C., lithium manganate particles having high crystallinity cannot be obtained. If the temperature is higher than 1000 ° C., it is difficult to obtain a single phase, which affects the battery characteristics.
[0083]
The firing atmosphere may be an oxygen-containing gas, for example, air. The firing time may be selected so that the reaction proceeds uniformly, but is preferably 1 to 48 hours, more preferably 10 to 24 hours.
[0084]
After firing, the powder is pulverized to obtain lithium manganate particles.
[0085]
Next, the nonaqueous electrolyte secondary battery according to the present invention will be described.
[0086]
When a positive electrode material is produced using the lithium manganate particles according to the present invention as a positive electrode active material for a non-aqueous electrolyte secondary battery, a conductive agent such as acetylene black and carbon black, and polytetrafluoroethylene and polyfluoroethylene are used. It is mixed with a binder such as vinylidene fluoride and shaped into a predetermined shape to form a positive electrode material.
[0087]
The negative electrode active material is not particularly limited, and for example, a lithium metal, a lithium alloy, or a substance capable of inserting and extracting lithium can be used, and examples thereof include a lithium / aluminum alloy, a lithium / tin alloy, graphite, and graphite. Can be
[0088]
Further, the electrolyte is not particularly limited. For example, lithium perchlorate, tetrafluoroboric acid, and the like are contained in at least one organic solvent such as carbonates such as propylene carbonate, diethyl carbonate, and dimethyl carbonate, and ethers such as dimethoxyethane. A solution in which at least one lithium salt such as lithium and lithium hexafluorophosphate is dissolved can be used.
[0089]
The secondary battery manufactured using the positive electrode active material according to the present invention has an initial discharge capacity of 60 to 135 mAh / g and a capacity retention after 100 cycles at 60 ° C of 90% or more.
[0090]
BEST MODE FOR CARRYING OUT THE INVENTION
A typical embodiment of the present invention is as follows.
[0091]
The particle diameter of the particle powder was measured by the following two methods.
[0092]
The average primary particle diameter of each particle powder was measured with a scanning electron microscope (manufactured by Hitachi, Ltd.). Ten primary particles were arbitrarily selected from the particles present on the diagonal line of the scanning electron microscope photograph, the particle diameter was measured, and the average value was defined as the average primary particle diameter. In the scanning electron micrograph, the magnification at which 20 to 40 particles are present on a diagonal line is preferable from the viewpoint of measuring accuracy of the particle diameter.
[0093]
The average secondary particle diameter of the particle powder is determined by the laser scattering / diffraction method "NIKKISO MICROTRAC HRA, Model 9320-X100: manufactured by Nikkiso Co., Ltd." 50 Was measured to obtain an average secondary particle diameter.
[0094]
The identification, crystal structure and crystallite size of the positive electrode active material were examined by X-ray diffraction (RIGAKU Cu-Kα 40 kV 40 mA).
[0095]
The morphology of the particles was observed with a scanning electron microscope (manufactured by Hitachi, Ltd.).
[0096]
The BET specific surface area was measured by the BET method.
[0097]
The tap density was measured by using "SEISHIN TADENSER KYT-3000: manufactured by Seishin Enterprise Co., Ltd."
[0098]
<Preparation of positive electrode>
Lithium manganate particles, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder are mixed at a weight ratio of 85: 10: 5, and N-methyl-2-pyrrolidone is added to form a paste. Was applied to an aluminum foil to a thickness of 0.15 mm, dried and punched out into a 16 mm-diameter disk to produce a positive electrode.
[0099]
A lithium foil was used as the negative electrode, and this was punched into a 16 mm disk shape.
[0100]
<Preparation of secondary battery>
The separator was made of polyethylene, and was punched into a 19 mm disk shape. LiPF for electrolyte 6 A mixture obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1: 1 using as a supporting salt was used. Then, a coin cell battery was manufactured in a glove box in an argon atmosphere.
[0101]
In the charge / discharge cycle test of the secondary battery, the current density with respect to the positive electrode was 0.5 mA / cm. 2 After charge / discharge was repeated 100 cycles at a temperature of 60 ° C. with a cutoff voltage of 4.5 V to 3.0 V, the discharge capacity was measured to determine the ratio to the initial discharge capacity.
[0102]
<Production of trimanganese tetroxide particle powder: (Production according to the present invention 2)>
Under nitrogen aeration, 277.9 l of a 2.0 mol / l manganese sulfate aqueous solution was added to 157.8 l of an 18.2 mol / l aqueous sodium hydroxide solution to make the total amount 700 L, and a neutralization reaction was carried out to perform manganese hydroxide particles. Was obtained. At this time, the manganese concentration was 0.8 mol / L, and the excess alkali concentration was 2.5 mol / L. The temperature of the obtained aqueous suspension containing manganese hydroxide particles was increased to 90 ° C. under nitrogen aeration, and then air was passed to perform an oxidation reaction at 90 ° C. Next, 138.9 l of a 0.4 mol / l manganese sulfate aqueous solution was added as a secondary reaction, and then the air was ventilated to carry out an oxidation reaction at 60 ° C, washed with water and dried to obtain manganese oxide particle powder. The amount of manganese salt added in the secondary reaction was half of the manganese concentration in the primary reaction.
[0103]
The obtained trimanganese tetroxide particle powder is Mn. 3 O 4 Having an average primary particle diameter of 9.0 μm and a BET specific surface area of 0.4 m. 2 / G. The Na content was 0.01% by weight and the S content was 0.001% by weight. FIG. 1 shows the observation results of a scanning electron microscope photograph of the obtained trimanganese tetroxide particles. As shown in the figure, the particle shape was a polyhedron or an octahedron having triangular or square faces.
[0104]
<Production of lithium manganate particles>
The thus obtained trimanganese tetroxide particles powder and lithium carbonate were mixed for 30 minutes so that the ratio of Li / Mn was 0.62, to obtain a uniform mixture. The obtained mixture was placed in an alumina sheath and kept at 845 ° C. in an air atmosphere for 6 hours to obtain lithium manganate particles.
[0105]
The obtained lithium manganate particles had an average primary particle size of 9.0 μm and an average secondary particle size (D 50 ) 11.9 μm, the Na content was 0.019%, and the S content was 0.001%. 0.3m BET specific surface area 2 / G and tap density was 2.3 g / ml. FIG. 2 shows the observation results of the scanning electron micrograph of the obtained lithium manganate particles. As shown in the figure, the particle shape was an isotropic polyhedron without an acute angle portion.
[0106]
The coin battery manufactured using the positive electrode active material comprising the lithium manganate particles obtained here had an initial discharge capacity of 91 mAh / g and a capacity retention rate of 98% / 100 cycles after 100 cycles at 60 ° C. Was.
[0107]
[Action]
The most important point in the present invention is that the trimanganese tetroxide particles and lithium manganate according to the present invention have a large primary particle diameter and are excellent in dispersibility without aggregation.
[0108]
In the present invention, although the reason is not clear, by separating the reaction into a primary reaction and a secondary reaction, it is possible to suppress the precipitation of a Na-Mn-based compound which is an impurity phase, and further, an organic-based reducing agent is used. By providing an aging step or performing an oxidation reaction in a high alkali region, tri-oxides having a large primary particle size, a uniform particle size distribution, small particle agglomeration, and a low Na and S content are provided. Manganese particles can be obtained.
[0109]
Since the particle size of the lithium manganate particles largely depends on the particle size of the trimanganese tetroxide particles serving as the precursor, by using the trimanganese tetroxide particles, the positive electrode active material composed of the lithium manganate particles also has a large primary It becomes particles, has few aggregated particles, has excellent particle size distribution, and can reduce the content of Na and S.
[0110]
The charge / discharge cycle characteristics of the secondary battery using the positive electrode active material according to the present invention are excellent because the specific surface area of the positive electrode active material is small, and the particle shape is an isotropic polyhedron and does not have an acute angle portion. Therefore, it is presumed that the reactivity with the electrolytic solution is suppressed, and the dispersibility and the filling property during coating are excellent.
[0111]
【Example】
Next, examples and comparative examples will be described.
[0112]
Examples 1-4, Comparative Examples 1-4
Trimanganese tetroxide was obtained in the same manner as in the embodiment of the invention except that the manganese salt concentration in the primary reaction and the secondary reaction was variously changed.
[0113]
Table 1 shows the production conditions at this time and various characteristics of the obtained trimanganese tetroxide particles.
[0114]
[Table 1]
Example 5: (Production according to the present invention 3)
Under nitrogen aeration, 277.9 l of a 2.0 mol / l manganese sulfate aqueous solution was added to 157.8 l of an 18.2 mol / l aqueous sodium hydroxide solution to make the total amount 700 L, and a neutralization reaction was carried out to perform manganese hydroxide particles. Was obtained. At this time, the manganese concentration was 0.8 mol / L, and the excess alkali concentration was 2.5 mol / L. The temperature of the obtained aqueous suspension containing manganese hydroxide particles was increased to 90 ° C. under aeration of nitrogen, and then the air was passed to perform an oxidation reaction at 90 ° C. Thereafter, the mixture was aged for 1 hour under nitrogen aeration. Next, 138.9 l of a 0.4 mol / l manganese sulfate aqueous solution was added as a secondary reaction, and then the air was ventilated to carry out an oxidation reaction at 60 ° C, washed with water and dried to obtain manganese oxide particle powder.
[0116]
The obtained trimanganese tetroxide particle powder is Mn. 3 O 4 Having an average primary particle diameter of 9.0 μm and a BET specific surface area of 0.3 m. 2 / G. The Na content was 0.005% by weight, and the S content was 0.001% by weight. As a result of observing the obtained trimanganese tetroxide particles in a scanning electron microscope photograph, the particle shape was an octahedron or an isotropic polyhedron having square to hexagonal surfaces.
[0117]
Examples 6 to 7, Comparative Examples 5 and 6
Trimanganese tetroxide was obtained in the same manner as in Example 5 except that the aging time was variously changed.
[0118]
Table 2 shows the production conditions at this time and various characteristics of the obtained trimanganese tetroxide particles.
[0119]
[Table 2]
Example 8: (Production according to the present invention 4)
Under nitrogen aeration, 277.9 l of a 2.0 mol / l manganese sulfate aqueous solution and 98 g of ascorbic acid were added to 157.8 l of an 18.2 mol / l aqueous sodium hydroxide solution to make the total amount 700 L, and a neutralization reaction was carried out. An aqueous suspension containing manganese hydroxide particles was obtained. At this time, the manganese concentration was 0.8 mol / L, the excess alkali concentration was 2.5 mol / l, and the added amount of ascorbic acid was 0.008 mol% based on manganese. The resulting aqueous suspension containing the manganese hydroxide particles was aged at 90 ° C. for 1 hour under nitrogen aeration. After aging, air was passed through to carry out an oxidation reaction at 90 ° C. Next, 138.9 l of a 0.4 mol / l manganese sulfate aqueous solution was added as a secondary reaction, and then the air was ventilated to carry out an oxidation reaction at 60 ° C, washed with water and dried to obtain manganese oxide particle powder.
[0121]
The obtained trimanganese tetroxide particle powder is Mn. 3 O 4 Having an average primary particle diameter of 9.0 μm and a BET specific surface area of 0.3 m. 2 / G. The Na content was 0.007% by weight, and the S content was 0.001% by weight. As a result of observing a scanning electron microscope photograph of the obtained trimanganese tetroxide particles, the particle shape was octahedron or isotropic polyhedron having square to hexagonal surfaces.
[0122]
Examples 9 to 11, Comparative Examples 7 and 8
Trimanganese tetroxide particles were obtained in the same manner as in Example 8 except that the amount of ascorbic acid with respect to manganese was variously changed.
[0123]
Table 3 shows the production conditions at this time and various properties of the obtained trimanganese tetroxide particles.
[0124]
[Table 3]
Example 12: (Production according to Invention 5)
Under nitrogen aeration, 277.9 liters of a 2.0 mol / l aqueous solution of manganese sulfate were added to 102.7 liters of an aqueous solution of 18.2 mol / l sodium hydroxide to make the total amount 700 L, and a neutralization reaction was carried out to perform manganese hydroxide particles. Was obtained. At this time, the manganese concentration was 0.8 mol / L, and the excess alkali concentration was 1.5 mol / L. Air was passed through the obtained aqueous suspension containing manganese hydroxide particles to perform an oxidation reaction at 90 ° C. Next, 138.9 l of a 0.4 mol / l manganese sulfate aqueous solution was added as a secondary reaction, and then the air was ventilated to carry out an oxidation reaction at 60 ° C, washed with water and dried to obtain manganese oxide particle powder.
[0126]
The obtained trimanganese tetroxide particle powder is Mn. 3 O 4 Having an average primary particle diameter of 6.0 μm and a BET specific surface area of 0.5 m. 2 / G. The Na content was 0.007% by weight, and the S content was 0.001% by weight. As a result of observing a scanning electron microscope photograph of the obtained trimanganese tetroxide particles, the particle shape was octahedron or isotropic polyhedron having square to hexagonal surfaces.
[0127]
Examples 13 to 15, Comparative Examples 9 to 11
Trimanganese tetroxide was obtained in the same manner as in Example 12 except that the amount of excess alkali for the primary reaction was variously changed.
[0128]
Table 4 shows the production conditions at this time and various characteristics of the obtained trimanganese tetroxide particles. Comparative Example 11 is electrolytic manganese dioxide (EMD).
[0129]
[Table 4]
Example 16: (Production according to the present invention 6)
Under nitrogen aeration, 277.9 l of 2.0 mol / l manganese sulfate aqueous solution and 490 g of ascorbic acid were added to 157.8 l of 18.2 mol / l sodium hydroxide aqueous solution to make the total amount 700 L, and a neutralization reaction was performed. An aqueous suspension containing manganese hydroxide particles was obtained. At this time, the manganese concentration was 0.8 mol / L, the excess alkali concentration was 2.5 mol / l, and the amount of ascorbic acid added was 0.05 mol% based on manganese. The temperature of the obtained aqueous suspension containing manganese hydroxide particles was increased to 90 ° C. under aeration of nitrogen, and then the air was passed to perform an oxidation reaction at 90 ° C. Thereafter, the mixture was aged for 2 hours under nitrogen aeration. Next, 138.9 l of a 0.4 mol / l manganese sulfate aqueous solution was added as a secondary reaction, and then the air was ventilated to carry out an oxidation reaction at 60 ° C, washed with water and dried to obtain manganese oxide particle powder. The amount of manganese salt added in the secondary reaction was half of the manganese concentration in the primary reaction.
[0131]
Table 5 shows properties of the obtained trimanganese tetroxide particles. As a result of observing a scanning electron microscope photograph of the obtained trimanganese tetroxide particles, the particle shape was octahedron or isotropic polyhedron having square to hexagonal surfaces.
[0132]
Example 17
Trimanganese tetroxide was obtained in the same manner as in Example 16 except that the reaction conditions were variously changed.
[0133]
Table 5 shows the production conditions at this time and various characteristics of the obtained trimanganese tetroxide particles.
[0134]
[Table 5]
Examples 18 to 34, Comparative Examples 12 to 22
Lithium manganate particles were obtained in the same manner as in <Production of lithium manganate particles> of the embodiment of the present invention, except that the type of trimanganese tetroxide particles was variously changed.
[0136]
Table 6 shows the production conditions at this time, various characteristics of the lithium manganate particles, and the results of battery evaluation performed in the same manner as in the embodiment of the invention.
[0137]
Each of the lithium manganate particles obtained in the examples had an isotropic polyhedron without sharp corners.
[0138]
[Table 6]
【The invention's effect】
The trimanganese tetroxide particle powder according to the present invention has a large average primary particle diameter and a small Na content and a small S content, and thus is suitable as a precursor of the lithium manganate particles.
[0140]
The positive electrode active material according to the present invention has a large average primary particle diameter, a low Na content and a small S content, and excellent dispersibility and filling properties. A battery can be provided.
[0141]
The secondary battery according to the present invention, by using the positive electrode active material, exhibits an initial discharge capacity substantially equal to a theoretical value, and is excellent in cycle characteristics at high temperatures, and thus is suitable as a secondary battery. .
[Brief description of the drawings]
FIG. 1 shows an electron micrograph (× 3500) of trimanganese tetroxide particles obtained in an embodiment of the present invention.
FIG. 2 shows an electron micrograph (× 3500) of a positive electrode active material composed of lithium manganate particles obtained in the embodiment of the present invention.
FIG. 3 shows an electron micrograph (× 3500) of electrolytic manganese dioxide used in Comparative Example 11.
FIG. 4 shows an electron micrograph (× 3500) of the lithium manganate particles obtained in Comparative Example 22.
Claims (9)
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