JP4179075B2 - Method for producing lithium manganese composite oxide granules - Google Patents
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- JP4179075B2 JP4179075B2 JP2003196285A JP2003196285A JP4179075B2 JP 4179075 B2 JP4179075 B2 JP 4179075B2 JP 2003196285 A JP2003196285 A JP 2003196285A JP 2003196285 A JP2003196285 A JP 2003196285A JP 4179075 B2 JP4179075 B2 JP 4179075B2
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
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Description
【０００１】
【発明の属する技術分野】
本発明は、リチウムマンガン複合酸化物顆粒体の製造方法に関するものである。
【０００２】
マンガン酸化物は、電池活物質として、古くから使用されている材料であり、リチウムマンガン複合酸化物は、リチウム二次電池の正極活物質として、近年注目されている材料である。
【０００３】
【従来の技術】
リチウムマンガン複合酸化物を非水電解質二次電池の正極活物質として使用する際、結晶一次粒子が燒結した適当な大きさの顆粒体からなる粉末が用いられている。顆粒体の製造方法としては、従来からいくつかの方法が適用されてきた。例えば、電解二酸化マンガンと炭酸リチウムの反応からリチウムマンガン複合酸化物を得る際、出発物質である電解二酸化マンガンの大きさを粉砕調整することにより、反応後もその大きさを保った顆粒体とする方法が開示されており（特許文献１）、電解二酸化マンガン粉末を水溶性リチウム化合物の水溶液に分散させたスラリーを噴霧乾燥し、造粒して顆粒体とする方法が開示され（特許文献２）、さらに、微粉末をローラコンパクター等を用い圧密・塊成化して顆粒体とする方法が開示されている（特許文献３、および特許文献４）。これらの公知文献からも知られるように、従来は電池の体積当たりの放電容量を高める観点から、顆粒体をできるだけ緻密にし、粉末の充填密度を高くすることに重点がおかれてきた。従って、これまで顆粒体の組織、特に内在する気孔について特徴付けた例は少ない。
【０００４】
特徴付けたものとしては、正極活物質の粒子内部に空孔を形成させることによりハイレート充放電特性およびサイクル特性に優れる正極活物質を提供しようとするものが開示されている（特許文献５）。しかしこの空孔から粒子外部環境へのリチウムイオンの拡散が十分におこなわれておらず、ハイレート特性およびサイクル特性の改善が不十分なものであった。即ち、その明細書第５頁の表２に、ハイレート充放電特性として２．０クーロン通電した時の容量と０．２クーロン通電した時の容量の比で評価しているが、その容量比は９０％以下となり、ハイレート充放電特性としては不十分である。
【０００５】
又、リチウムイオン二次電池用の正極には、サイクル特性に優れる事が求められている。しかし、リチウムマンガン複合酸化物は複合酸化物であるゆえに組成のばらつき等が発生し易く、性能に与える影響が問題となる。この対策として、焼成条件を工夫してサイクル維持率を向上させる方法が開示されている（特許文献６）が、効果が十分でない上に原料焼成および、反応焼成の２回の焼成を必要とし、実用化が困難であった。
【０００６】
【特許文献１】
特開２０００−１６９１５１号公報
【特許文献２】
特開平１０−１７２５６７号公報
【特許文献３】
特開平１０−２２８５１５号公報
【特許文献４】
特開平１０−２９７９２４号公報
【特許文献５】
特開２００２−７５３６５号公報
【特許文献６】
特開２０００−２６０４３０号公報
【発明が解決しようとする課題】
本発明は、リチウムマンガン複合酸化物顆粒体の組織、特に顆粒内の開気孔形態を制御する製造方法により、サイクル特性及びハイレート特性の向上した正極材料として使用するリチウムマンガン複合酸化物顆粒体を提供することを目的とした。
【０００７】
【課題を解決するための手段】
リチウムマンガン複合酸化物前駆体を特定の焼成条件にて焼成することにより、顆粒内にマイクロメーターサイズの開気孔が網目状に多数存在し、かつ組成のばらつき無く均一なリチウムマンガン複合酸化物が製造できることを見出し、本発明の高放電特性、高サイクル特性を示す非水電解質二次電池の正極活物質として適するリチウムマンガン複合酸化物の製造方法に到達した。本発明の最大の特徴はリチウムマンガン複合酸化物が均一な結晶相であり、かつ顆粒内にマイクロメーターサイズの開気孔を網目状に多数存在することにある。この結果として、電池の高サイクル特性の向上および放電特性の向上が図れる。
【０００８】
【作用】
以下、本発明を具体的に説明する。
【０００９】
本発明は、マンガン酸化物及び炭酸リチウムを含む分散スラリー、または、マンガン酸化物、炭酸リチウム及びＡｌ、Ｃｏ、Ｎｉ、Ｃｒ、Ｆｅ、Ｍｇ及びＢの群から選ばれる１種以上の元素の化合物を含む分散スラリーを噴霧乾燥によりリチウムマンガン複合酸化物前駆体を製造し、該前駆体を酸素含有雰囲気中５００℃以上、７５０℃未満の温度で２時間以上保持する第一加熱処理、温度が第一加熱処理のそれよりも５０℃以上高く、かつ酸素含有雰囲気中７５０℃〜９５０℃で２時間以上保持する第二加熱処理、さらに第二加熱処理の温度よりも低く、かつ酸素含有雰囲気中６００℃〜９００℃の温度で３時間以上保持する第三加熱処理を行うことを必須とする。
【００１０】
特に、結晶相が均一で、かつ開気孔の網目状構造を均一化させた、マイクロメーターサイズの開気孔が多数存在し、その開気孔の平均径が０．５〜３μｍの範囲にあり、且つその開気孔の全体積が、顆粒全体積に対して平均３〜２０ｖｏｌ．％の範囲にある、リチウムマンガン複合酸化物顆粒体が製造できる。
【００１１】
全ての加熱処理は全て酸素含有雰囲気中で行うことが好ましい。
【００１２】
第一加熱処理において、保持温度は６００〜７００℃、処理時間は５〜４８時間が好ましく、第二加熱処理において、保持温度は８００〜９００℃、処理時間は５〜４８時間が好ましい。第一加熱処理および第二加熱処理の温度は一定値が好ましいが、経時的に変化させても良い。
【００１３】
また、第三加熱処理においては、連続的および／または段階的に温度を変化させることが好ましく、その温度の変化速度は単位時間あたりの平均変化速度として１０℃／ｈｒより大きく１００℃／ｈｒ以下が好ましく、１０℃／ｈｒより大きく５０℃／ｈｒ以下がさらに好ましい。
【００１４】
加熱処理条件が前記範囲外であると、生成物の平均一次粒子径が所望の範囲外となる等の原因により、開気孔の網目状構造の形成および組成の均一化が達成できない。
【００１５】
得られるリチウムマンガン複合酸化物の顆粒体の開気孔構造は、そのマイクロメーターサイズの開気孔は大きさと量で規定され、大きさは平均径として０．５〜３μｍ、気孔の割合は顆粒体積に対して平均３〜２０ｖｏｌ．％である。気孔の平均径が０．５μｍ未満では電池の放電レート特性が低下する。また、３μｍを越えるとの開気孔になると顆粒の強度を保つことが困難となる。最も好ましい平均径は１．０〜２．５μｍの範囲である。気孔の割合は、３ｖｏｌ．％未満では電池の放電レート特性が低下する。
【００１６】
また２０ｖｏｌ．％を越えると電極材料として要求される高い粉末充填密度を確保することが困難となる。最も好ましい気孔の割合は５〜１５ｖｏｌ．％である。
【００１７】
なお、気孔の平均径及び量は気孔を球形近似して求められる値であり、測定方法として顆粒の切断面の走査型電子顕微鏡写真を撮り、画像解析処理する方法によって知ることができ、ここでは気孔数５００個以上の平均から求めた個数平均値とする。
【００１８】
リチウムマンガン複合酸化物前駆体を加熱処理する焼成炉は特に制限されないが連続型のトンネル炉または、回分式の箱型電気炉を用いることが好ましい。
リチウムマンガン複合酸化物前駆体は、マンガン酸化物及びリチウム化合物を含む分散スラリー、または、マンガン酸化物、炭酸リチウム及びＡｌ，Ｃｏ，Ｎｉ，Ｃｒ，Ｆｅ，Ｍｇ，Ｂの群から選ばれる１種以上の元素の化合物を含む分散スラリーを噴霧乾燥により顆粒化したものであることが必須である。
【００１９】
マンガン酸化物の粉末としては特に制限されないが、電解二酸化マンガン、化学合成二酸化マンガン、Ｍｎ3Ｏ4、Ｍｎ2Ｏ3等が挙げられる。この中でも純度が高いことから電解二酸化マンガンが好適に用いられる。
【００２０】
マンガン酸化物及び炭酸リチウムの他に分散スラリーに添加する化合物として、Ａｌ，Ｃｏ，Ｎｉ，Ｃｒ，Ｆｅ，Ｍｇ，Ｂから選ばれる１種以上の元素の化合物としては、それらの酸化物、塩、酸、水酸化物、例えば、水酸化アルミニウム、水酸化ニッケル、酸化クロム及びホウ酸等を用いてもよい。
【００２１】
これにより焼成時にリチウムマンガン複合酸化物の顆粒体中の一次粒子結晶がさらに均一に成長する。
【００２２】
マンガン酸化物、炭酸リチウム、その他の化合物が水に溶解せずにスラリー中で粒子として存在する場合、その平均粒子径は１μｍ以下であることが好ましく、０．３〜０．７μｍであることがさらに好ましい。何故ならば、平均粒子径が１μｍより大きい場合には、焼成時の反応性が悪く、開気孔の網目状構造が不均一となり好ましくない。
【００２３】
このような粒子サイズはマンガン酸化物の粉末と炭酸リチウムの粉末または、マンガン酸化物と炭酸リチウムおよび添加化合物の粉末を水に入れ、粉砕混合することで容易に達成される。粉砕混合装置としては、ボールミル、振動ミル、湿式媒体攪拌式ミル等が使用できる。
【００２４】
湿式粉砕混合されたスラリーは噴霧乾燥により顆粒化される。噴霧乾燥はスラリーを回転ディスク、或いは流体ノズルで噴霧し、液滴を熱風で乾燥する通常のスプレードライヤーで行うことができる。顆粒化の方法として、噴霧乾燥以外の方法例えば液中造粒法、転動造粒法等が適用できるが、噴霧乾燥が最も工業的に有利である。
【００２５】
マンガン酸化物、炭酸リチウム以外にホウ素化合物を用いる場合、ホウ素化合物は加熱処理後、ホウ酸化合物として結晶表面に残存する。残存した結晶表面のホウ酸化合物は電池性能に悪影響を及ぼすため、水洗によりホウ素のマンガンに対するモル比で０．０００５以下になるまで除去することを必須とする。
【００２６】
ホウ酸化合物が電池性能に影響しない好ましい範囲はマンガンに対するモル比で０＜Ｂ／Ｍｎ＜０．０００５であり、０＜Ｂ／Ｍｎ＜０．０００３であることがさらに好ましい。
【００２７】
本発明の製造方法で得られるリチウムマンガン複合酸化物顆粒体を正極活物質として用いた非水電解質二次電池は優れた放電特性およびサイクル特性を示す。この優れた放電特性およびサイクル特性は、本発明のリチウムマンガン複合酸化物の顆粒体内に存在する均一な網目状の多数の開気孔および組成の均一化からもたらされたものと推定される。すなわち、放電レートはリチウムイオンの正極活物質内での輸送のされ易さに応じて良くなるが、正極活物質が多数の開気孔により網目状組織と化した結果、リチウムイオンの物質内〜外部電解液間の輸送距離が短くなり、輸送が容易になったものと推定される。サイクル特性は、リチウムマンガン複合酸化物の組成の均一化により理想に近い充放電が行えることによりもたらされたものと推定される。
【００２８】
また製造したリチウムマンガン複合酸化物顆粒体は適宜、解砕、分級を行うことが好ましい。
【００２９】
【実施例】
以下の実施例により、本発明を具体的に説明するが、これら実施例により本発明は何等限定されるものでない。
【００３０】
尚、得られたリチウムマンガン複合酸化物顆粒体の開気孔の平均径と量、及びそのリチウムマンガン複合酸化物顆粒体を正極とした時のサイクル特性及び放電特性は以下に示す方法で測定した。
［開気孔の平均径と量］
顆粒体の断面写真を走査型電子顕微鏡により撮影した。この際、粉末を硬化性樹脂に埋め込み、表面研磨によって顆粒の切断面を露出させたものを撮影試料とした。電顕写真の画像解析処理を行い、顆粒体内に存在する開気孔の平均径と量を求めた。なお、開気孔平均径は気孔数５００〜１０００個について個数平均値を採った。
［サイクル特性］
試料と導電剤／結着剤（アセチレンブラック／テフロン（登録商標））を混合して正極物質とし、負極物質として金属リチウムを、電解液としてＬｉＰＦ6を溶解させたエチレンカーボネート／ジメチルカーボネート溶液を用いコインセル型電池を作成した。充放電試験は６０℃で電流密度０．４ｍＡ／ｃｍ2、電圧４．３〜３．０Ｖの範囲で行った。サイクル特性はサイクル維持率（１０回目と５０回目の放電容量の比率）で評価した。
［放電特性］
試料粉末と導電剤／結着剤（アセチレンブラック／テフロン（登録商標）系樹脂）を混合して正極活物質とし、負極活物質として金属リチウムを、電解液としてＬｉＰＦ6を溶解させたエチレンカーボネート／ジメチルカーボネート溶液を用いコインセル型電池を作成した。これらの電池について室温にて放電レートを測定した。
放電特性をレート維持率（０．３Ｃでの放電容量を基準としたときの５．５Ｃでの放電容量の比率）と放電容量で評価した。
【００３１】
実施例１
炭酸リチウム粉末（平均粒子径７μｍ）と電解二酸化マンガン粉末（平均粒子径３μｍ）及びホウ酸を組成Ｌｉ1.1Ｍｎ1.9Ｂ0.01Ｏ4になるように秤量し、水を適量加えた後、湿式媒体攪拌式ミルで１時間粉砕した。粉砕後の固形分の平均粒子径は０．７μｍであった。固形分濃度が１５ｗｔ％のスラリーとなるように水を加えて調整し、噴霧乾燥装置により水を蒸発させ、球状のリチウムマンガン複合酸化物前駆体を得た。噴霧乾燥は熱風入口温度２５０℃で行った。この乾燥粉末を以下の条件で加熱処理した。
第一加熱処理：６００℃、 ６時間、大気中
第二加熱処理：８００℃、２４時間、大気中
第三加熱処理：７００℃、２４時間、大気中
得られたリチウムマンガン複合酸化物顆粒体は、Ｘ繰回折パターンがＪＣＰＤＳ３５−７８２に近いパターンを示す立方晶スピネル単相であった。
【００３２】
このリチウムマンガン複合酸化物顆粒体をさらに９５℃温水浴中で１時間洗浄し、濾過後乾燥して試料を得た。
【００３３】
この試料中のホウ素含有量を測定したところ、５０ｐｐｍ以下であった。
【００３４】
この試料について、開気孔の平均径と量、サイクル特性、放電特性を測定した。
【００３５】
実施例２
実施例１において加熱処理を以下の条件で行った以外は同一とした。
第一加熱処理：６００℃、 ６時間、大気中
第二加熱処理：９００℃、 ６時間、大気中
第三加熱処理：８００℃、２４時間、大気中
得られたリチウムマンガン複合酸化物顆粒体は、Ｘ繰回折パターンがＪＣＰＤＳ３５−７８２に近いパターンを示す立方晶スピネル単相であった。
【００３６】
このリチウムマンガン複合酸化物顆粒体をさらに９５℃温水浴中で１時間洗浄し、濾過後乾燥して試料を得た。
【００３７】
この試料中のホウ素含有量を測定したところ、５０ｐｐｍ以下であった。
【００３８】
この試料について、開気孔の平均径と量、サイクル特性、放電特性を測定した。
【００３９】
実施例３〜５
実施例２で用いた炭酸リチウム、電解二酸化マンガン、ホウ酸の各粉末以外に添加剤（Ｍ）として、水酸化アルミニウム、酸化クロム、水酸化ニッケルの各粉末を追加して、組成Ｌｉ1.1Ｍ0.1Ｍｎ1.8Ｂ0.01Ｏ4（Ｍ＝Ａｌ、Ｃｒ又はＮｉ）となるように秤量し加熱処理を以下の条件で行った以外は同一とした。
第一加熱処理：６５０℃、 ６時間、大気中
第二加熱処理：８５０℃、 ６時間、大気中
第三加熱処理：８５０〜６００℃、５時間、大気中、降温速度５０℃／ｈｒ
得られたリチウムマンガン複合酸化物顆粒体は、Ｘ繰回折パターンがＪＣＰＤＳ３５−７８２に近いパターンを示す立方晶スピネル単相であった。
【００４０】
このリチウムマンガン複合酸化物顆粒体をさらに９５℃温水浴中で１時間洗浄し、濾過後乾燥して試料を得た。
【００４１】
この試料中のホウ素含有量を測定したところ、５０ｐｐｍ以下であった。
【００４２】
この試料について、開気孔の平均径と量、サイクル特性、放電特性を測定した。
【００４３】
実施例６〜８
実施例２で用いた炭酸リチウム、電解二酸化マンガン、ホウ酸の各粉末以外に添加剤（Ｍ）として、水酸化アルミニウム、酸化クロム、水酸化ニッケルの各粉末を追加して、組成Ｌｉ1.1Ｍ0.1Ｍｎ1.8Ｂ0.01Ｏ4（Ｍ＝Ａｌ、Ｃｒ又はＮｉ）となるように秤量し加熱処理を以下の条件で行った以外は同一とした。
第一加熱処理：６００℃、 ４８時間、大気中
第二加熱処理：９００℃、 ６時間、大気中
第三加熱処理：９００〜６００℃、１５時間、大気中、降温速度２０℃／ｈｒ
得られたリチウムマンガン複合酸化物顆粒体は、Ｘ繰回折パターンがＪＣＰＤＳ３５−７８２に近いパターンを示す立方晶スピネル単相であった。
【００４４】
このリチウムマンガン複合酸化物顆粒体をさらに９５℃温水浴中で１時間洗浄し、濾過後乾燥して試料を得た。
【００４５】
この試料中のホウ素含有量を測定したところ、５０ｐｐｍ以下であった。
【００４６】
この試料について、開気孔の平均径と量、サイクル特性、放電特性を測定した。
【００４７】
比較例１
第二加熱処理を１０００℃で行った以外は、実施例３と同一の条件で行った。
【００４８】
比較例２
第二加熱処理を１０００℃で行った以外は、実施例２と同一の条件で行った。
【００４９】
比較例３
第一加熱処理を８００℃、第二加熱処理を９５０℃，第三加熱処理を９００〜６００℃，降温速度５０℃／ｈｒで行った以外は、実施例３と同一の条件で行った。
【００５０】
比較例４
第一加熱処理を４５０℃、第二加熱処理を７５０℃，第三加熱処理を６００℃，で行った以外は、実施例３と同一の条件で行った。
【００５１】
比較例５
第一加熱処理を５００℃、第二加熱処理を７００℃，第三加熱処理を７００〜６００℃，降温速度５０℃／ｈｒで行った以外は、実施例３と同一の条件で行った。
【００５２】
比較例６
第一加熱処理を５５０℃、第二加熱処理を７５０℃，第三加熱処理を５００℃で行った以外は、実施例３と同一の条件で行った。
【００５３】
比較例７
第二加熱処理を９５０℃，第三加熱処理を９２０℃で行った以外は、実施例３と同一の条件で行った。
【００５４】
実施例１〜８および比較例１〜７で得られたリチウムマンガン複合酸化物顆粒体の開気孔の平均径と量、及びそのリチウムマンガン複合酸化物顆粒体を正極に使用した時のサイクル特性及び放電特性を表１に示す。
【００５５】
【表１】
【００５６】
【発明の効果】
本発明の製造方法によって得られるリチウムマンガン複合酸化物顆粒体は非水電解質二次電池の正極活物質として優れた放電特性およびサイクル特性を示す。従って、高出力リチウムイオン二次電池の正極材料として特に有用である。リチウムイオン二次電池の高出力化および高サイクル特性は電気自動車用途では特に要求されており、そのための有効な材料となる。それ以外のリチウムイオン二次電池の用途、例えば電力貯蔵用、携帯機器用等の電源においても有用な正極材料として利用でき、工業的利用価値は高い。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a lithium manganese composite oxide granule.
[0002]
Manganese oxide is a material that has been used for a long time as a battery active material, and lithium manganese composite oxide is a material that has recently attracted attention as a positive electrode active material for lithium secondary batteries.
[0003]
[Prior art]
When a lithium manganese composite oxide is used as a positive electrode active material of a non-aqueous electrolyte secondary battery, a powder made of an appropriately sized granule in which crystalline primary particles are sintered is used. As a method for producing a granule, several methods have been conventionally applied. For example, when obtaining a lithium manganese composite oxide from the reaction of electrolytic manganese dioxide and lithium carbonate, the size of the electrolytic manganese dioxide that is the starting material is adjusted by crushing to obtain a granule that maintains its size after the reaction. A method is disclosed (Patent Document 1), and a method is disclosed in which a slurry in which electrolytic manganese dioxide powder is dispersed in an aqueous solution of a water-soluble lithium compound is spray-dried and granulated into granules (Patent Document 2). Furthermore, a method is disclosed in which a fine powder is compacted and agglomerated using a roller compactor to form granules (Patent Document 3 and Patent Document 4). As known from these known documents, conventionally, in order to increase the discharge capacity per volume of the battery, emphasis has been placed on making the granules as dense as possible and increasing the packing density of the powder. Thus, few examples have been characterized to date of granule tissue, especially the intrinsic pores.
[0004]
What has been characterized is that a positive electrode active material that is excellent in high-rate charge / discharge characteristics and cycle characteristics is disclosed by forming pores inside the particles of the positive electrode active material (Patent Document 5). However, the diffusion of lithium ions from the vacancies to the external environment of the particles has not been sufficiently performed, and the improvement of the high rate characteristics and the cycle characteristics has been insufficient. That is, in Table 2 on page 5 of the specification, the high rate charge / discharge characteristics are evaluated by the ratio of the capacity when energized with 2.0 coulombs and the capacity when energized with 0.2 coulombs. It is 90% or less, which is insufficient as a high rate charge / discharge characteristic.
[0005]
Moreover, it is calculated | required that the positive electrode for lithium ion secondary batteries is excellent in cycling characteristics. However, since the lithium-manganese composite oxide is a composite oxide, composition variations and the like are likely to occur, and the effect on performance becomes a problem. As a countermeasure against this, a method for improving the cycle retention rate by devising the firing conditions has been disclosed (Patent Document 6), but the effect is not sufficient, and two firings of raw material firing and reaction firing are required, It was difficult to put it into practical use.
[0006]
[Patent Document 1]
JP 2000-169151 A [Patent Document 2]
JP 10-172567 A [Patent Document 3]
Japanese Patent Laid-Open No. 10-228515 [Patent Document 4]
JP-A-10-297924 [Patent Document 5]
JP 2002-75365 A [Patent Document 6]
JP 2000-260430 A [Problems to be Solved by the Invention]
The present invention provides a lithium manganese composite oxide granule to be used as a positive electrode material having improved cycle characteristics and high rate characteristics by a production method for controlling the structure of lithium manganese composite oxide granules, particularly the open pore shape in the granules. Aimed to do.
[0007]
[Means for Solving the Problems]
By firing the lithium-manganese composite oxide precursor under specific firing conditions, a uniform lithium-manganese composite oxide with many micrometer-sized open pores in the granules and uniform composition is produced. As a result, the inventors have reached a method for producing a lithium manganese composite oxide suitable as a positive electrode active material of a non-aqueous electrolyte secondary battery exhibiting high discharge characteristics and high cycle characteristics of the present invention. The greatest feature of the present invention is that the lithium manganese composite oxide has a uniform crystal phase, and a large number of micrometer-sized open pores are present in a network. As a result, the high cycle characteristics and the discharge characteristics of the battery can be improved.
[0008]
[Action]
The present invention will be specifically described below.
[0009]
The present invention provides a dispersion slurry containing manganese oxide and lithium carbonate, or a compound of one or more elements selected from the group consisting of manganese oxide, lithium carbonate and Al, Co, Ni, Cr, Fe, Mg, and B. A first heat treatment in which a lithium manganese composite oxide precursor is produced by spray-drying the dispersed slurry, and the precursor is held in an oxygen-containing atmosphere at a temperature of 500 ° C. or higher and lower than 750 ° C. for 2 hours or more; high 50 ° C. or higher than that of the heat treatment, and second heat treatment for holding at least 2 hours at 750 ° C. to 950 ° C. in an oxygen-containing atmosphere, even lower than the temperature of the second heat treatment, and an oxygen-containing atmosphere 600 ° C. It is essential to perform the third heat treatment for 3 hours or more at a temperature of ˜900 ° C.
[0010]
In particular, there are many micrometer-sized open pores having a uniform crystal phase and uniform open pore network structure, and the average diameter of the open pores is in the range of 0.5 to 3 μm, and The total volume of open pores averaged 3 to 20 vol. % Lithium manganese composite oxide granules can be produced.
[0011]
All heat treatments are preferably performed in an oxygen-containing atmosphere.
[0012]
In the first heat treatment, the holding temperature is 600 to 700 ° C. and the treatment time is preferably 5 to 48 hours. In the second heat treatment, the holding temperature is 800 to 900 ° C. and the treatment time is preferably 5 to 48 hours. The temperature of the first heat treatment and the second heat treatment is preferably a constant value, but may be changed with time.
[0013]
In the third heat treatment, it is preferable to change the temperature continuously and / or stepwise, and the change rate of the temperature is greater than 10 ° C./hr and not more than 100 ° C./hr as an average change rate per unit time. Is preferable, more preferably 10 ° C./hr and 50 ° C./hr or less.
[0014]
When the heat treatment condition is outside the above range, formation of a network structure of open pores and uniform composition cannot be achieved due to factors such as the average primary particle diameter of the product being outside the desired range.
[0015]
The open pore structure of the resulting lithium manganese composite oxide granules is defined by the size and amount of open pores of the micrometer size, the size is 0.5 to 3 μm as an average diameter, and the proportion of pores is the granule volume. On the average 3-20 vol. %. When the average pore diameter is less than 0.5 μm, the discharge rate characteristics of the battery are degraded. Further, when the open pore size exceeds 3 μm, it is difficult to maintain the strength of the granules. The most preferable average diameter is in the range of 1.0 to 2.5 μm. The ratio of pores was 3 vol. If it is less than%, the discharge rate characteristics of the battery deteriorate.
[0016]
In addition, 20 vol. If it exceeds 50%, it becomes difficult to ensure a high powder packing density required as an electrode material. The most preferable pore ratio is 5 to 15 vol. %.
[0017]
The average diameter and amount of the pores are values obtained by approximating the pores in a spherical shape, and can be known by taking a scanning electron micrograph of the cut surface of the granule as a measurement method and performing image analysis processing. The number average value obtained from the average of 500 or more pores is used.
[0018]
The firing furnace for heat-treating the lithium manganese composite oxide precursor is not particularly limited, but it is preferable to use a continuous tunnel furnace or a batch-type box electric furnace.
The lithium manganese composite oxide precursor is a dispersion slurry containing manganese oxide and a lithium compound, or one or more selected from the group consisting of manganese oxide, lithium carbonate, and Al, Co, Ni, Cr, Fe, Mg, and B It is essential that the dispersion slurry containing the compound of the element is granulated by spray drying.
[0019]
The manganese oxide powder is not particularly limited, and examples thereof include electrolytic manganese dioxide, chemically synthesized manganese dioxide, Mn 3 O 4 , and Mn 2 O 3 . Among these, electrolytic manganese dioxide is preferably used because of its high purity.
[0020]
As a compound to be added to the dispersion slurry in addition to manganese oxide and lithium carbonate, as a compound of one or more elements selected from Al, Co, Ni, Cr, Fe, Mg, B, those oxides, salts, Acids, hydroxides such as aluminum hydroxide, nickel hydroxide, chromium oxide and boric acid may be used.
[0021]
Thereby, the primary particle crystal in the granule of the lithium manganese composite oxide grows more uniformly during firing.
[0022]
When manganese oxide, lithium carbonate, and other compounds are present as particles in the slurry without dissolving in water, the average particle size is preferably 1 μm or less, and preferably 0.3 to 0.7 μm. Further preferred. This is because when the average particle size is larger than 1 μm, the reactivity during firing is poor, and the network structure of the open pores is not preferable.
[0023]
Such a particle size can be easily achieved by putting manganese oxide powder and lithium carbonate powder or manganese oxide, lithium carbonate and additive compound powder in water and pulverizing and mixing them. As the pulverizing and mixing apparatus, a ball mill, a vibration mill, a wet medium stirring mill, or the like can be used.
[0024]
The wet pulverized and mixed slurry is granulated by spray drying. Spray drying can be performed with a normal spray dryer in which the slurry is sprayed with a rotating disk or a fluid nozzle and the droplets are dried with hot air. As a granulation method, methods other than spray drying such as submerged granulation method and rolling granulation method can be applied, but spray drying is most industrially advantageous.
[0025]
When a boron compound is used in addition to manganese oxide and lithium carbonate, the boron compound remains on the crystal surface as a boric acid compound after heat treatment. Since boric acid compound remaining crystals surfaces adversely affect the battery performance and essential and removing until 0.0005 in terms of a molar ratio to boron of manganese by washing with water.
[0026]
A preferable range in which the boric acid compound does not affect the battery performance is 0 <B / Mn <0.0005 in terms of molar ratio to manganese, and more preferably 0 <B / Mn <0.0003.
[0027]
A non-aqueous electrolyte secondary battery using a lithium manganese composite oxide granule obtained by the production method of the present invention as a positive electrode active material exhibits excellent discharge characteristics and cycle characteristics. The excellent discharge characteristics and cycle characteristics are presumed to have resulted from the uniform network-like numerous open pores present in the granules of the lithium manganese composite oxide of the present invention and the homogenization of the composition. In other words, the discharge rate is improved depending on the ease of transport of lithium ions in the positive electrode active material, but the positive electrode active material is converted into a network structure by a large number of open pores, and as a result, the lithium ion material has an internal to external surface. It is presumed that the transport distance between the electrolytes has been shortened and transport has become easier. It is presumed that the cycle characteristics are brought about by being able to perform charge / discharge close to ideal by making the composition of the lithium manganese composite oxide uniform.
[0028]
Moreover, it is preferable that the produced lithium manganese composite oxide granules are appropriately crushed and classified.
[0029]
【Example】
The present invention will be specifically described by the following examples, but the present invention is not limited to these examples.
[0030]
The average diameter and amount of open pores of the obtained lithium manganese composite oxide granules, and the cycle characteristics and discharge characteristics when the lithium manganese composite oxide granules were used as a positive electrode were measured by the following methods.
[Average diameter and amount of open pores]
A cross-sectional photograph of the granule was taken with a scanning electron microscope. At this time, a photograph sample was prepared by embedding the powder in a curable resin and exposing the cut surface of the granules by surface polishing. Electron microscopic image analysis was performed to determine the average diameter and amount of open pores present in the granules. The average open pore diameter was a number average value for 500 to 1000 pores.
[Cycle characteristics]
A sample and a conductive agent / binder (acetylene black / Teflon (registered trademark)) are mixed to form a positive electrode material, metallic lithium as a negative electrode material, and an ethylene carbonate / dimethyl carbonate solution in which LiPF 6 is dissolved as an electrolytic solution. A coin cell battery was created. The charge / discharge test was performed at 60 ° C. in a current density of 0.4 mA / cm 2 and a voltage of 4.3 to 3.0 V. The cycle characteristics were evaluated by a cycle maintenance ratio (ratio of discharge capacity at the 10th time and 50th time).
[Discharge characteristics]
A sample powder and a conductive agent / binder (acetylene black / Teflon (registered trademark) resin) are mixed to form a positive electrode active material, metallic lithium as a negative electrode active material, and ethylene carbonate / LiPF 6 dissolved as an electrolytic solution / A coin cell type battery was prepared using a dimethyl carbonate solution. The discharge rate of these batteries was measured at room temperature.
The discharge characteristics were evaluated by the rate maintenance rate (ratio of discharge capacity at 5.5 C with reference to discharge capacity at 0.3 C) and discharge capacity.
[0031]
Example 1
Lithium carbonate powder (average particle size 7 μm), electrolytic manganese dioxide powder (average particle size 3 μm), and boric acid were weighed so as to have the composition Li 1.1 Mn 1.9 B 0.01 O 4 , and an appropriate amount of water was added. It grind | pulverized for 1 hour with a formula mill. The average particle size of the solid content after pulverization was 0.7 μm. Water was added and adjusted so as to obtain a slurry having a solid content concentration of 15 wt%, and water was evaporated by a spray dryer to obtain a spherical lithium manganese composite oxide precursor. Spray drying was performed at a hot air inlet temperature of 250 ° C. This dry powder was heat-treated under the following conditions.
First heat treatment: 600 ° C., 6 hours, second heat treatment in air: 800 ° C., 24 hours, third heat treatment in air: 700 ° C., 24 hours, lithium manganese composite oxide granules obtained in air X-ray diffraction pattern was a cubic spinel single phase showing a pattern close to JCPDS35-782.
[0032]
This lithium manganese composite oxide granule was further washed in a warm water bath at 95 ° C. for 1 hour, filtered and dried to obtain a sample.
[0033]
The boron content in this sample was measured and found to be 50 ppm or less.
[0034]
For this sample, the average diameter and amount of open pores, cycle characteristics, and discharge characteristics were measured.
[0035]
Example 2
In Example 1, it was the same except having performed heat processing on the following conditions.
First heat treatment: 600 ° C., 6 hours, second heat treatment in air: 900 ° C., 6 hours, third heat treatment in air: 800 ° C., 24 hours, lithium manganese composite oxide granules obtained in air X-ray diffraction pattern was a cubic spinel single phase showing a pattern close to JCPDS35-782.
[0036]
This lithium manganese composite oxide granule was further washed in a warm water bath at 95 ° C. for 1 hour, filtered and dried to obtain a sample.
[0037]
The boron content in this sample was measured and found to be 50 ppm or less.
[0038]
For this sample, the average diameter and amount of open pores, cycle characteristics, and discharge characteristics were measured.
[0039]
Examples 3-5
In addition to the powders of lithium carbonate, electrolytic manganese dioxide, and boric acid used in Example 2, as additives (M), powders of aluminum hydroxide, chromium oxide, and nickel hydroxide were added, and the composition Li 1.1 M 0.1 Mn 1.8 B 0.01 O 4 (M = Al, Cr or Ni) except under the following conditions weighed heat treatment so that were the same.
First heat treatment: 650 ° C., 6 hours, second heat treatment in air: 850 ° C., 6 hours, third heat treatment in air: 850-600 ° C., 5 hours, in air, cooling rate of 50 ° C./hr
The obtained lithium manganese composite oxide granule was a cubic spinel single phase having an X-refraction diffraction pattern close to JCPDS35-782.
[0040]
This lithium manganese composite oxide granule was further washed in a warm water bath at 95 ° C. for 1 hour, filtered and dried to obtain a sample.
[0041]
The boron content in this sample was measured and found to be 50 ppm or less.
[0042]
For this sample, the average diameter and amount of open pores, cycle characteristics, and discharge characteristics were measured.
[0043]
Examples 6-8
In addition to the powders of lithium carbonate, electrolytic manganese dioxide, and boric acid used in Example 2, as additives (M), powders of aluminum hydroxide, chromium oxide, and nickel hydroxide were added, and the composition Li 1.1 M 0.1 Mn 1.8 B 0.01 O 4 (M = Al, Cr or Ni) except under the following conditions weighed heat treatment so that were the same.
First heat treatment: 600 ° C., 48 hours, second heat treatment in air: 900 ° C., 6 hours, third heat treatment in air: 900-600 ° C., 15 hours, in air, temperature decreasing rate 20 ° C./hr
The obtained lithium manganese composite oxide granule was a cubic spinel single phase having an X-refraction diffraction pattern close to JCPDS35-782.
[0044]
This lithium manganese composite oxide granule was further washed in a warm water bath at 95 ° C. for 1 hour, filtered and dried to obtain a sample.
[0045]
The boron content in this sample was measured and found to be 50 ppm or less.
[0046]
For this sample, the average diameter and amount of open pores, cycle characteristics, and discharge characteristics were measured.
[0047]
Comparative Example 1
The second heat treatment was performed under the same conditions as in Example 3 except that the second heat treatment was performed at 1000 ° C.
[0048]
Comparative Example 2
The second heat treatment was performed under the same conditions as in Example 2 except that the second heat treatment was performed at 1000 ° C.
[0049]
Comparative Example 3
The first heat treatment was carried out under the same conditions as in Example 3 except that the second heat treatment was carried out at 950 ° C., the third heat treatment was carried out at 900 to 600 ° C., and the cooling rate was 50 ° C./hr.
[0050]
Comparative Example 4
The first heat treatment was performed at 450 ° C., the second heat treatment was performed at 750 ° C., and the third heat treatment was performed at 600 ° C. under the same conditions as in Example 3.
[0051]
Comparative Example 5
The first heat treatment was carried out under the same conditions as in Example 3 except that the second heat treatment was carried out at 700 ° C., the third heat treatment was carried out at 700 to 600 ° C., and the cooling rate was 50 ° C./hr.
[0052]
Comparative Example 6
The first heat treatment was performed at 550 ° C., the second heat treatment was performed at 750 ° C., and the third heat treatment was performed at 500 ° C. under the same conditions as in Example 3.
[0053]
Comparative Example 7
The second heat treatment was performed under the same conditions as in Example 3 except that the second heat treatment was performed at 950 ° C. and the third heat treatment was performed at 920 ° C.
[0054]
Average diameter and amount of open pores of the lithium manganese composite oxide granules obtained in Examples 1 to 8 and Comparative Examples 1 to 7, and cycle characteristics when the lithium manganese composite oxide granules were used for the positive electrode and The discharge characteristics are shown in Table 1.
[0055]
[Table 1]
[0056]
【The invention's effect】
The lithium manganese composite oxide granule obtained by the production method of the present invention exhibits excellent discharge characteristics and cycle characteristics as a positive electrode active material of a non-aqueous electrolyte secondary battery. Therefore, it is particularly useful as a positive electrode material for high-power lithium ion secondary batteries. High output and high cycle characteristics of a lithium ion secondary battery are particularly required in electric vehicle applications, and are effective materials for that purpose. It can be used as a positive electrode material that is useful in other uses of lithium ion secondary batteries, for example, power supplies for power storage and portable devices, and has high industrial utility value.
Claims (6)
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| DE102008029804A1 (en) * | 2008-06-24 | 2010-07-08 | Süd-Chemie AG | Mixed oxide containing a lithium manganese spinel and process for its preparation |
| BRPI1007247A2 (en) * | 2009-01-20 | 2019-02-26 | Toda Kogyo Corp | Positive electrode active material for secondary batteries as non-aqueous electrolyte solution, process for the production of active material and secondary batteries with non-aqueous electrolyte solution. |
| JP2010260733A (en) * | 2009-04-30 | 2010-11-18 | Murata Mfg Co Ltd | Manganese-containing lithium transition metal multiple oxide and method for producing the same |
| KR101272042B1 (en) | 2010-11-08 | 2013-06-07 | 주식회사 포스코이에스엠 | Lithuium manganese complex oxide and the manufacturing method thereof |
| KR101547632B1 (en) | 2012-09-21 | 2015-08-27 | 주식회사 포스코이에스엠 | 5 5 manufacuring method of 5 spinel complex-oxide 5 spinel complex-oxide made by the same and lithium rechargeable batteries comprising the same |
| WO2014136760A1 (en) * | 2013-03-04 | 2014-09-12 | 三井金属鉱業株式会社 | Lithium metal composite oxide powder |
| KR101854482B1 (en) * | 2013-08-21 | 2018-05-03 | 주식회사 엘지화학 | A method of making a lithium secondary battery and a lithium secondary battery manufactured therefrom |
| CN109075337B (en) * | 2016-06-23 | 2021-10-22 | 日立金属株式会社 | Method for producing positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery |
| WO2021045025A1 (en) * | 2019-09-06 | 2021-03-11 | 日立金属株式会社 | Positive electrode active material for lithium ion secondary batteries, method for producing same, and lithium ion secondary battery |
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