JP3922040B2 - Lithium manganese composite oxide, method for producing the same, and use thereof - Google Patents
Lithium manganese composite oxide, method for producing the same, and use thereof Download PDFInfo
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- JP3922040B2 JP3922040B2 JP2002038482A JP2002038482A JP3922040B2 JP 3922040 B2 JP3922040 B2 JP 3922040B2 JP 2002038482 A JP2002038482 A JP 2002038482A JP 2002038482 A JP2002038482 A JP 2002038482A JP 3922040 B2 JP3922040 B2 JP 3922040B2
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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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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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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酸化物の改良に関するものであって、詳しくは、一般式Ｌｉ［Ｍｎ2-X-YＬｉXＭY］Ｏ4+ δ（式中Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上であり、０．０２≦Ｘ≦０．１０、０．０５≦Ｙ≦０．３０、−０．２≦δ≦０．２）で表され、ＳＥＭ観察による結晶粒子の平均径が２μ以下であり、ＣｕＫαによる粉末Ｘ線回折の（４００）面の半値幅が ０．２２°以下であることを特徴とするスピネル型結晶構造のリチウムマンガン複合酸化物、及び、そのＢＥＴ比表面積が１．０ｍ2・ｇ-1以下であることを特徴とするスピネル型結晶構造のリチウムマンガン複合酸化物、さらにはこれらを製造可能とするＭｎ−Ｍ複合酸化物スラリー原料とこれらの製造方法、及び、そのリチウムマンガン酸化物を正極活物質に用いるリチウム二次電池に関するものである。
【０００２】
リチウム二次電池は、高エネルギー密度であることから、次世代を担う新型二次電池として幅広い分野への適用が進められており、既に一部で実用化されたものも含めて、さらなる高性能化を目指した研究が進められている。
【０００３】
マンガン系材料は、原料のマンガンが資源的に豊富で安価、かつ、環境に対して優しい材料であることから有望な材料のひとつである。
【０００４】
【従来の技術】
モバイル機器の普及に伴って、小型、軽量、高エネルギー密度のリチウム二次電池が強く望まれるようになり、負極にリチウムを吸蔵、放出可能な炭素質材料を用いたリチウムイオン電池が実用化された。
【０００５】
現在のリチウムイオン電池の正極材料には、リチウムコバルト酸化物（以下ＬｉＣｏＯ2と表記）が主に使用されているが、コバルト原料が高価であることから代替材料の開発が望まれている。
【０００６】
ＬｉＣｏＯ2に代わる４Ｖ級の起電力を示す正極材料としては、リチウムニッケル酸化物（以下ＬｉＮｉＯ2と表記）やリチウムマンガンスピネル（以下ＬｉＭｎ2Ｏ4と表記）が挙げられるが、資源的に豊富で安価であり、環境への影響が小さいこと、電池にした場合の安全性が確保し易いことなどから、ハイブリッドタイプの電気自動車用電池や燃料電池用補助電源としてＬｉＭｎ2Ｏ4が最も優れた正極材料と考えられており、実用化に向けて精力的な研究開発が行われている。
【０００７】
しかしながら、ＬｉＭｎ2Ｏ4は高温安定性、すなわち、高温における充放電での容量低下や保存特性などに問題があることが指摘されており、この課題の解決が望まれていた。
【０００８】
例えば、ＬｉＭｎ2Ｏ4にＡｌをドープした、ＬｉXＭｎ(2-Y)ＡｌYＯ4（特開平４−２８９６６２）やＬｉ［Ｍｎ2-X-YＬｉXＭｅY］Ｏ4（特開平１１−７９５６）が提案されているが、充放電を５０サイクル繰返した後での容量維持率が最大９６％までであり、未だ改善の余地を残している。
【０００９】
【発明が解決しようとする課題】
本発明の目的は、高温安定性を改良したリチウムマンガン酸化物とその製造方法を提案し、さらに、この化合物を正極活物質に用いた高出力なリチウム二次電池を提供することにある。
【００１０】
【課題を解決するための手段】
ＬｉＭｎ2Ｏ4の高温安定性、すなわち、高温での充放電サイクル特性や保存特性を向上させることを目的に鋭意検討を行った結果、電解二酸化マンガンをマンガン原料として、あらかじめＭ（Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上）の金属塩水溶液中で攪拌しながらアルカリを加えてＭｎ−Ｍ複合酸化物スラリー原料を製造し、これにリチウム原料を加えて大気中、または、高濃度酸素雰囲気中（純粋酸素雰囲気中を含む）、即ち、酸素濃度が１８〜１００％の雰囲気中で焼成することによって、一般式Ｌｉ［Ｍｎ2-X-YＬｉXＭY］Ｏ4+ δ（式中Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上であり、０．０２≦Ｘ≦０．１０、０．０５≦Ｙ≦０．３０、−０．２≦δ≦０．２）で表され、ＣｕＫαによる粉末Ｘ線回折の（４００）面の半値幅が０．２２°以下であり、且つ、ＳＥＭ観察による結晶粒子の平均径が２μ以下のスピネル型結晶構造のリチウムマンガン複合酸化物、及び、ＢＥＴ比表面積が１．０ｍ2・ｇ-1以下のスピネル型結晶構造のリチウムマンガン複合酸化物が合成可能であり、さらに、これをリチウム二次電池の正極活物質に用いることで、従来の材料では達成することができなかった高温安定性が大幅に改良されたマンガン系リチウム二次電池が構成できることを見出し、本発明を完成するに至った。
【００１１】
【作用】
以下、本発明を具体的に説明する。
【００１２】
本発明は、一般式Ｌｉ［Ｍｎ2-X-YＬｉXＭY］Ｏ4+ δ（式中Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上であり、０．０２≦Ｘ≦０．１０、０．０５≦Ｙ≦０．３０、−０．２≦δ≦０．２）で表されるスピネル型結晶構造のリチウムマンガン複合酸化物である。
【００１３】
本発明の化合物は、リチウム，マンガン，金属元素Ｍ（ここで、Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上の元素），および酸素で構成され、立方最密充填した酸素パッキングの四面体位置にリチウムが、八面体位置にマンガンと金属元素Ｍ、又はリチウムとマンガン並びに金属元素Ｍが占有している。Ｍとしては、Ｍｇ、Ｎｉ、Ａｌ、Ｆｅなどが例示される。通常、四面体位置と八面体位置の数の比率は１：２であり、リチウム、マンガン、金属元素Ｍの各サイトの占有率は上記一般式の範囲であればスピネル型結晶構造の酸化物となる。この場合、四面体位置を８ａサイト、八面体位置を１６ｄサイトとよんでいる。
【００１４】
本発明のリチウムマンガン酸化物は、リチウム、マンガンおよび酸素の各元素以外に第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上の元素を含むことが重要である。これらの元素を含有させることによって高温での安定性が改善される。これらの元素の含有量は、一般式Ｌｉ［Ｍｎ2-X-YＬｉXＭY］Ｏ4+ δにおいて、０．０２≦Ｘ≦０．１０、０．０５≦Ｙ≦０．３０、−０．２≦δ≦０．２であることが必須である。Ｘの値がこれを超えて小さいと十分な高温安定性が保てず、これを超えて大きいと高温安定性は保てるが満足な充放電容量が得られない。また、Ｙの値がこれを超えて小さいと元素Ｍの含有効果が小さいため満足な高温安定性が保てず、これを超えて大きいと高温安定性は保てるが十分な充放電容量が得られない。
【００１５】
又、酸素原子数を表すδ値は、−０．２≦δ≦０．２の範囲を取る様に規定されているが、このδ値を厳密に測定し決定することは分析上非常に困難であり、通常の表記（化学式）では０とする。
【００１６】
本発明のリチウムマンガン酸化物は、ＳＥＭ観察による結晶粒子の平均径が２μ以下であり、且つ、ＣｕＫαによる粉末Ｘ線回折の（４００）面の半値幅が０．２２°以下であることが必須である。本発明のリチウムマンガン酸化物は、スピネル構造の１６ｄサイトにそれぞれイオン半径の異なるＬｉとＭｎ、及び、Ｍ（Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上の元素）が均一に分散していることが重要であり、これらが均一に分散していれば単一相となるため粉末Ｘ線回折の半値幅は十分小さくなり問題ないが、これら元素が偏析しているとそれらのイオン半径に依存して格子定数の異なる結晶粒子の集合体となるため、格子定数の少しづつ異なるスピネル型結晶の集合体となり粉末Ｘ線回折の半値幅は増大する。すなわち、粉末Ｘ線回折の半値幅は結晶粒子間の組成の不均一性をあらわす指標であり、これが大きいとこれらの元素Ｍを含有させることによる高温安定性の改善効果が十分に発揮できない。
【００１７】
本発明のリチウムマンガン酸化物は、ＳＥＭ観察による結晶粒子の平均径が２μ以下であることが必須であり、ＢＥＴ比表面積が１．０ｍ2・ｇ-1以下であることが好ましい。リチウムマンガン酸化物の結晶粒子は、酸素欠陥を介して粒成長する性質があり、ＳＥＭ観察による結晶粒子が５μ以上のものは高温安定性を損なう酸素欠陥を多く内在している。結晶粒子径が２μ以下であれば実質的に酸素欠陥の影響がほとんどなく、その結晶粒子が均一にそろっていることは特に好ましい。一方、結晶粒子が小さいとＢＥＴ比表面積が大きくなり、電解液との接触面積が増えるためハイレート充放電に対しては有利な傾向があるが、高温安定性の低下、電極作製時の作業性、歩留まりなどが悪くなる。ＢＥＴ比表面積を小さくするのには結晶粒子を大きくすればよいが、結晶粒子があまりにも大きいと上記のような理由で満足な高温安定性を得ることができない。そのため、結晶粒子の平均径が２μ以下であり、かつ、ＢＥＴ比表面積が１．０ｍ2・ｇ-1以下であることが好ましい。
【００１８】
本発明で示すように、高温安定性を大幅に改善する為には、化学組成、すなわち、これまでに知られているような金属元素Ｍ（Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上の元素）が単に添加されているのみでなく、その粉末Ｘ線回折の（４００）面の半値幅が０．２２°以下であることが重要であり、ＳＥＭ観察による結晶粒子の平均径が２μ以下、かつ、ＢＥＴ比表面積が１．０ｍ2・ｇ-1以下であることが特に重要である。これらによって、十分な高温安定性を得ることが初めて可能となる。
【００１９】
本発明のリチウムマンガン酸化物は、電解二酸化マンガンをマンガン原料として、Ｍ（Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上）の金属塩水溶液中で攪拌しながらアルカリを加えることで製造されるＭｎ−Ｍ複合酸化物スラリーを原料とすることで製造できる。これにリチウム原料を加えたて大気中、または、高濃度酸素雰囲気中（純粋酸素雰囲気中を含む）、即ち、酸素濃度１８〜１００％の雰囲気中で焼成することによって本発明のリチウムマンガン酸化物が得られる。
【００２０】
本発明のリチウムマンガン酸化物の合成において、電解二酸化マンガンをマンガン原料として用いることが重要である。電解二酸化マンガンは、通常、ＢＥＴ比表面積が約３０〜４０ｍ2／ｇと大きく、これをＭ（Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上）の金属塩水溶液中で攪拌することで、Ｍをその表面に均一に吸着させることができ、さらに、アンモニア水等のアルカリを加えてこれを表面に固定化させることができる。攪拌は室温で行っても良いが水溶液の沸点以下の高温で行っても良い。合成に用いる金属元素Ｍの原料は、水溶性の塩であればいかなるものを用いてもよく、硝酸塩、硫酸塩、等が例示される。このようにして製造したＭｎ−Ｍ複合酸化物スラリーは、そのまま用いてもよいが、乾燥してから用いてもよく、また、焼成して例えばＭを含有するＭｎ2Ｏ3やＭｎ3Ｏ4のような低級酸化物にしてから用いてもよい。
【００２１】
合成に用いるリチウム原料は、例えば、炭酸リチウム、水酸化リチウム、硝酸リチウム、酢酸リチウム、ヨウ化リチウムなどの、マンガン酸化物と５００℃以下の温度で複合化反応が始まる化合物であればいかなるものを用いても良く、これらを乾式で混合しても、スラリー化あるいは溶解して湿式で混合してもよいが、混合性あるいは溶解性をよくするために平均粒径が５μｍ以下、さらに望ましくは２μ以下のリチウム原料を用いることが特に好ましい。
【００２２】
本発明のリチウムマンガン酸化物を得る為の焼成は、大気中もしくは高濃度酸素雰囲気中（純粋酸素雰囲気を含む）、即ち、酸素含有量が１８％〜１００％の酸素雰囲気中で行い、焼成温度は７００℃以上９５０℃以下の範囲が望ましい。これより低温ではＢＥＴ比表面積を十分小さくするために非常に長時間を要し、これより高温では結晶粒子が異常成長し易くなる。さらに、リチウムマンガン酸化物は高温時に酸素を放出吸収する性質があることから、酸素の吸収を考慮して焼成後の冷却速度を１時間当たり２０℃以下の速度で行うことはさらに好ましい。
【００２３】
本発明のリチウム二次電池の負極としては、リチウム金属、リチウム合金、リチウムを予め吸蔵した、リチウムを吸蔵放出可能な化合物を用いることができる。
【００２４】
リチウム合金としては、本発明を制限するものではないが、例えば、リチウム／スズ合金、リチウム／アルミニウム合金、リチウム／鉛合金等が例示される。
【００２５】
リチウムを吸蔵放出可能な化合物としては、本発明を制限するものではないが、例えば、グラファイトや黒鉛等の炭素材料や、鉄の酸化物、コバルトの酸化物が例示される。
【００２６】
また、本発明のリチウム二次電池の電解質は、特に制限されないが、例えば、炭酸プロレン、炭酸ジエチル等のカーボネート類や、スルホラン、ジメチルスルホキシド等のスルホラン類、γブチロラクトン等のラクトン類、ジメチルスルホキシド等のエーテル類の少なくとも１種類以上の有機溶媒に、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、トリフルオロメタンスルホン酸等のリチウム塩の少なくとも１種類以上を溶解したものや、無機系および有機系のリチウムイオン導電性の固体電解質などを用いることができる。
【００２７】
以下に、本発明の具体例として実施例を示すが、本発明はこれらの実施例により制限されるものではない。
【００２８】
なお、本発明の実施例および比較例における粉末Ｘ線回折測定は、以下に示す方法で行った。
【００２９】
粉末Ｘ線回折測定
測定機種 マックサイエンス社製 ＭＸＰ３
照射Ｘ線 Ｃｕ Ｋα線
測定モード ステップスキャン
スキャン条件 ２θとして０．０４°
計測時間 ５秒
測定範囲 ２θとして５°から８０°
また、ＢＥＴ比表面積は窒素吸着法によって、また、平均粒子径はマイクロトラックによって測定した。
【００３０】
【実施例】
［リチウムマンガン複合酸化物の製造］
実施例１
（Ｌｉ［Ｍｎ1.85Ｌｉ0.05Ｍｇ0.1］Ｏ4の合成）
実施例１として、Ｌｉ［Ｍｎ1.85Ｌｉ0.05Ｍｇ0.1］Ｏ4を以下の方法によって行った。
【００３１】
硫酸マグネシウム０．０５４モル／Ｌの水溶液１Ｌに電解二酸化マンガン８７ｇを投入して８０℃に加温しながら攪拌し、これに３ｗｔ％のアンモニア水１００ｍｌを約２時間かけて滴下しさらに４時間攪拌を行ったのち、濾過、乾燥させた。これを８００℃で１２時間焼成したのち、所定量の平均粒径２μの炭酸リチウムを乾式で混合し、８００℃で２４時間焼成した。粉末Ｘ線回折測定より得られた化合物はスピネル構造であること、及び、ＳＥＭ観察により結晶粒子は正八面体形状で大きさが良く揃っていることを確認した。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００３２】
実施例２
（Ｌｉ［Ｍｎ1.85Ｌｉ0.05Ｎｉ0.1］Ｏ4の合成）
実施例２として、Ｌｉ［Ｍｎ1.85Ｌｉ0.05Ｎｉ0.1］Ｏ4の合成を以下の方法によって行った。
【００３３】
硫酸ニッケル０．０５４モル／Ｌの水溶液１Ｌに電解二酸化マンガン８７ｇを投入して６０℃に加温しながら攪拌し、これに３ｗｔ％のアンモニア水１００ｍｌを約２時間かけて滴下しさらに４時間攪拌を行ったのち、濾過、乾燥させた。濾液は無色透明であることを確認した。これに、所定量の平均粒径２μの炭酸リチウムを乾式で混合し、８００℃で２４時間焼成した。粉末Ｘ線回折測定より得られた化合物はスピネル構造であること、及び、ＳＥＭ観察により結晶粒子は正八面体形状で大きさが良く揃っていることを確認した。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００３４】
実施例３
（Ｌｉ［Ｍｎ1.80Ｌｉ0.05Ａｌ0.15］Ｏ4の合成）
実施例３として、Ｌｉ［Ｍｎ1.80Ｌｉ0.05Ａｌ0.15］Ｏ4を以下の方法によって行った。
【００３５】
硫酸アルミニウム０．０８４モル／Ｌの水溶液１Ｌに電解二酸化マンガン８７ｇを投入して９０℃に加温しながら攪拌し、これに３ｗｔ％のアンモニア水１００ｍｌを約２時間かけて滴下しさらに４時間攪拌を行ったのち、濾過、乾燥させた。これを９００℃で１２時間焼成したのち、所定量の平均粒径２μの炭酸リチウムを乾式で混合し、９００℃で２４時間焼成した。粉末Ｘ線回折測定より得られた化合物はスピネル構造であること、及び、ＳＥＭ観察により結晶粒子は正八面体形状で大きさが良く揃っていることを確認した。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００３６】
実施例４
（Ｌｉ［Ｍｎ1.74Ｌｉ0.03Ａｌ0.23］Ｏ4の合成）
実施例４として、Ｌｉ過剰量とＡｌ添加量とを変えた以外は実施例３と同様にして、Ｌｉ［Ｍｎ1.74Ｌｉ0.03Ａｌ0.23］Ｏ4の合成を行った。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００３７】
実施例５
（Ｌｉ［Ｍｎ1.80Ｌｉ0.05Ｆｅ0.15］Ｏ4の合成）
実施例５として、Ｌｉ［Ｍｎ1.80Ｌｉ0.05Ｆｅ0.15］Ｏ4を以下の方法によって行った。
【００３８】
硫酸鉄（ＩＩ）０．０８４モル／Ｌの水溶液１Ｌに電解二酸化マンガン８７ｇを投入して室温で攪拌した。このとき、攪拌を中断すると上澄み液は初め２価鉄の淡い緑色であったものが、１時間の攪拌後には３価マンガン、あるいは、３価の鉄イオンに由来する黄褐色になっていた。これは、２価鉄と二酸化マンガンとの酸化還元反応によるものであり、鉄イオンは二酸化マンガン粒子の表面に強く作用しているものと考えられた。これに攪拌しながら３ｗｔ％のアンモニア水１００ｍｌを約２時間かけて滴下しさらに４時間攪拌を行ったのち、濾過、乾燥させた。濾液は無色透明であった。これを８００℃で１２時間焼成したのち、所定量の平均粒系２μの炭酸リチウムを乾式で混合し、８５０℃で２４時間焼成した。粉末Ｘ線回折測定より得られた化合物はスピネル構造であること、及び、ＳＥＭ観察により結晶粒子は正八面体形状で大きさが良く揃っていることを確認した。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００３９】
実施例６
（Ｌｉ［Ｍｎ1.80Ｌｉ0.05Ｍｇ0.05Ａｌ0.10］Ｏ4の合成）
実施例６として、Ｍｇ添加量とＡｌ添加量とを変えた以外は実施例３と同様にして、Ｌｉ［Ｍｎ1.80Ｌｉ0.05Ｍｇ0.05Ａｌ0.10］Ｏ4の合成を行った。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００４０】
比較例１
比較例１として、実施例１と同様の組成となるように、水酸化マグネシウム、炭酸リチウム、電解二酸化マンガンを秤量し、乾式混合したのち、８００℃２４時間の焼成を行い、Ｌｉ［Ｍｎ1.85Ｌｉ0.05Ｍｇ0.10］Ｏ4を合成した。ＳＥＭ観察より、結晶粒子は正八面体形状がよく発達したものであったが、５μ以上の粗大粒子と１μ以下の微細粒子が入り混じったものであった。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００４１】
比較例２
比較例２として、実施例６と同様の組成となるように、水酸化アルミニウム、炭酸リチウム、電解二酸化マンガンを秤量し、乾式混合したのち、９００℃２４時間の焼成を行いＬｉ［Ｍｎ1.80Ｌｉ0.05Ｍｇ0.05Ａｌ0.10］Ｏ4を合成した。ＳＥＭ観察より、結晶粒子は正八面体形状がよく発達したものであったが、比較例１と同様に５μ以上の粗大粒子と１μ以下の微細粒子が入り混じったものであった。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００４２】
比較例３
比較例３として、電解二酸化マンガンと炭酸リチウムを乾式で混合し、９００℃２４時間の焼成を行いＬｉ［Ｍｎ1.90Ｌｉ0.10］Ｏ4を合成した。ＳＥＭ観察より、結晶粒子は正八面体形状がよく発達したものであったが、比較例１と同様に５μ以上の粗大粒子と１μ以下の微細粒子が入り混じったものであった。生成物の化学組成分析結果、（４００）面の半値幅、ＳＥＭ観察による結晶粒子径、及び、ＢＥＴ比表面積を表１に示した。
【００４３】
【表１】
実施例１〜６及び比較例１〜３で製造したリチウムマンガン複合酸化物を、導電剤のポリテトラフルオロエチレンとアセチレンブラックとの混合物（商品名：ＴＡＢ−２）を重量比で２：１になるように混合した。混合物の７５ｍｇを１ｔｏｎ・ｃｍ-2の圧力で、１６ｍｍφのメッシュ（ＳＵＳ３１６）上にペレット状に成形した後に、２００℃で２時間の減圧乾燥処理を行った。
【００４４】
これを正極に用いて、負極にはリチウム箔（厚さ０．２ｍｍ）から切り抜いたリチウム片を用いて、電解液にはプロピレンカーボネートと炭酸ジメチルの体積比１：２の混合溶媒に、六フッ化リン酸リチウムを１ｍｏｌ・ｄｍ-3の濃度に溶解した有機電解液を用いて、電極面積２ｃｍ2の電池を構成した。
【００４５】
表２に、５０℃における容量維持率（５０サイクル目容量／１０サイクル目容量）を示した。
【００４６】
【表２】
【００４７】
【発明の効果】
以上に示した通り、電解二酸化マンガンをマンガン原料として、あらかじめＭ（Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上）の金属塩水溶液中で攪拌しながらアルカリを加えてＭｎ−Ｍ複合酸化物スラリーを製造し、これにリチウム原料を加えて大気中、または、高濃度酸素雰囲気中（純粋酸素雰囲気を含む）、即ち、酸素濃度１８〜１００％雰囲気中で焼成することによって、一般式Ｌｉ［Ｍｎ2-X-YＬｉXＭY］Ｏ4+ δ（式中Ｍは第２、第３周期のＩＩａ族、ＩＩＩｂ族、VＩＩＩ族から選ばれる少なくとも一種類以上であり、０．０２≦Ｘ≦０．１０、０．０５≦Ｙ≦０．３０、−０．２≦δ≦０．２）で表され、ＣｕＫαによる粉末Ｘ線回折の（４００）面の半値幅が０．２２°以下のスピネル型結晶構造であり、ＳＥＭ観察による結晶粒子の平均径が２μ以下であるリチウムマンガン複合酸化物、及び、ＢＥＴ比表面積が１．０ｍ2・ｇ-1以下のスピネル型結晶構造のリチウムマンガン複合酸化物が合成可能となり、これをリチウム二次電池の正極活物質に用いることで、従来の材料では達成することができなかった高温安定性が大幅に改良されたマンガン系リチウム二次電池が構成できることを見出した。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to improvement of a lithium manganese oxide, particularly, formula Li [Mn 2-XY Li X M Y] O 4+ δ ( wherein M represents a 2, IIa Group of the third period, At least one selected from group IIIb and group VIII, represented by 0.02 ≦ X ≦ 0.10, 0.05 ≦ Y ≦ 0.30, −0.2 ≦ δ ≦ 0.2), Lithium manganese composite oxidation of spinel type crystal structure characterized in that the average diameter of crystal grains by SEM observation is 2 μm or less and the half width of (400) plane of powder X-ray diffraction by CuKα is 0.22 ° or less And a lithium manganese composite oxide having a spinel crystal structure characterized by having a BET specific surface area of 1.0 m 2 · g −1 or less, and a Mn-M composite oxide capable of producing them Slurry raw materials and production methods thereof, and The present invention relates to a lithium secondary battery using the lithium manganese oxide as a positive electrode active material.
[0002]
Since lithium secondary batteries have high energy density, they are being applied to a wide range of fields as new secondary batteries that will lead the next generation, including those already in practical use. Research aimed at achieving this is underway.
[0003]
Manganese-based materials are one of the promising materials because the raw material manganese is abundant in resources, inexpensive, and environmentally friendly.
[0004]
[Prior art]
With the spread of mobile devices, small, light, and high energy density lithium secondary batteries are strongly desired, and lithium ion batteries using carbonaceous materials that can store and release lithium in the negative electrode have been put into practical use. It was.
[0005]
Lithium cobalt oxide (hereinafter referred to as LiCoO 2 ) is mainly used as the positive electrode material of current lithium ion batteries, but the development of alternative materials is desired because the cobalt raw material is expensive.
[0006]
Examples of the positive electrode material exhibiting a 4V class electromotive force replacing LiCoO 2 include lithium nickel oxide (hereinafter referred to as LiNiO 2 ) and lithium manganese spinel (hereinafter referred to as LiMn 2 O 4 ). LiMn 2 O 4 is the best positive electrode as an auxiliary power source for hybrid electric vehicles and fuel cells because it is inexpensive, has little impact on the environment, and it is easy to ensure safety when using batteries. It is considered a material, and energetic research and development is underway for practical application.
[0007]
However, it has been pointed out that LiMn 2 O 4 has problems with high-temperature stability, that is, capacity reduction and storage characteristics during charging and discharging at high temperatures, and a solution to this problem has been desired.
[0008]
For example, Al-doped to LiMn 2 O 4, Li X Mn (2-Y) Al Y O 4 ( JP-A-4-289662) and Li [Mn 2-XY Li X Me Y] O 4 ( JP-A-11- 7956) is proposed, but the capacity retention rate after 50 cycles of charge / discharge is up to 96%, and there is still room for improvement.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to propose a lithium manganese oxide with improved high-temperature stability and a method for producing the same, and to provide a high-power lithium secondary battery using this compound as a positive electrode active material.
[0010]
[Means for Solving the Problems]
As a result of intensive studies aimed at improving the high temperature stability of LiMn 2 O 4 , that is, the charge / discharge cycle characteristics and storage characteristics at high temperatures, electrolytic manganese dioxide was used as a manganese raw material in advance. And at least one selected from Group IIa, Group IIIb, and Group VIII of the third period) an alkali is added while stirring in an aqueous solution of a metal salt to produce a Mn-M composite oxide slurry raw material. Is added to the general formula Li [Mn 2-XY Li X by firing in the air or in a high concentration oxygen atmosphere (including a pure oxygen atmosphere), that is, in an atmosphere having an oxygen concentration of 18 to 100%. M Y ] O 4+ δ (wherein M is at least one selected from Group IIa, Group IIIb and Group VIII of the second and third periods, and 0.02 ≦ X ≦ 0.10, 0.05) ≦ ≦ 0.30, −0.2 ≦ δ ≦ 0.2), the full width at half maximum of (400) plane of powder X-ray diffraction by CuKα is 0.22 ° or less, and crystal grains by SEM observation A spinel-type crystal structure lithium manganese composite oxide having an average diameter of 2 μm or less and a spinel-type crystal structure lithium manganese composite oxide having a BET specific surface area of 1.0 m 2 · g −1 or less can be synthesized. Furthermore, by using this as a positive electrode active material of a lithium secondary battery, it was found that a manganese-based lithium secondary battery with significantly improved high-temperature stability that could not be achieved with conventional materials can be constructed. The invention has been completed.
[0011]
[Action]
The present invention will be specifically described below.
[0012]
The present invention has the general formula Li [Mn 2-XY Li X M Y] O 4+ δ ( wherein M represents a 2, IIa Group of the third period, IIIb group, is at least one or more selected from group VIII 0.02 ≦ X ≦ 0.10, 0.05 ≦ Y ≦ 0.30, −0.2 ≦ δ ≦ 0.2).
[0013]
The compound of the present invention is composed of lithium, manganese, a metal element M (where M is at least one element selected from Group IIa, Group IIIb, and Group VIII of the second and third periods) and oxygen. Further, lithium is occupied by tetrahedral positions of the oxygen packing packed in cubic close packing, and manganese and metal element M, or lithium, manganese and metal element M are occupied at octahedral positions. Examples of M include Mg, Ni, Al, and Fe. Usually, the ratio of the number of tetrahedral positions to octahedral positions is 1: 2, and the occupancy of each site of lithium, manganese, and metal element M is within the range of the above general formula. Become. In this case, the tetrahedron position is called 8a site, and the octahedron position is called 16d site.
[0014]
It is important that the lithium manganese oxide of the present invention contains at least one element selected from Group IIa, Group IIIb, and Group VIII of the second and third periods in addition to lithium, manganese, and oxygen elements. . By containing these elements, stability at high temperature is improved. The content of these elements, in the general formula Li [Mn 2-XY Li X M Y] O 4+ δ, 0.02 ≦ X ≦ 0.10,0.05 ≦ Y ≦ 0.30, -0. It is essential that 2 ≦ δ ≦ 0.2. If the value of X exceeds this value, sufficient high-temperature stability cannot be maintained. If it exceeds this value, high-temperature stability can be maintained, but satisfactory charge / discharge capacity cannot be obtained. If the Y value exceeds this value, the inclusion effect of the element M is small, so that satisfactory high-temperature stability cannot be maintained. If it exceeds this value, high-temperature stability can be maintained, but sufficient charge / discharge capacity can be obtained. Absent.
[0015]
In addition, the δ value representing the number of oxygen atoms is defined to take a range of −0.2 ≦ δ ≦ 0.2, but it is very difficult to analyze and determine this δ value strictly. It is 0 in normal notation (chemical formula).
[0016]
In the lithium manganese oxide of the present invention, it is essential that the average diameter of crystal particles by SEM observation is 2 μm or less, and the half width of (400) plane of powder X-ray diffraction by CuKα is 0.22 ° or less. It is. The lithium manganese oxide of the present invention has Li and Mn having different ionic radii at the 16d site of the spinel structure, and M (M is at least one selected from Group IIa, Group IIIb, and Group VIII of the second and third periods). It is important that more than one kind of element) is uniformly dispersed, and if these are uniformly dispersed, a single phase is obtained, so the half-value width of powder X-ray diffraction is sufficiently small and there is no problem. If segregated, it becomes an aggregate of crystal grains having different lattice constants depending on their ionic radii, resulting in an aggregate of spinel crystals with slightly different lattice constants, and the half-width of powder X-ray diffraction increases. . That is, the full width at half maximum of powder X-ray diffraction is an index representing the non-uniformity of the composition between crystal grains, and if this is large, the effect of improving the high temperature stability due to the inclusion of these elements M cannot be exhibited sufficiently.
[0017]
In the lithium manganese oxide of the present invention, it is essential that the average diameter of crystal particles by SEM observation is 2 μm or less, and the BET specific surface area is preferably 1.0 m 2 · g −1 or less. The crystal grains of lithium manganese oxide have the property of growing through oxygen defects, and those having crystal grains of 5 μm or more as observed by SEM have many oxygen defects that impair high-temperature stability. If the crystal grain size is 2 μm or less, it is particularly preferable that the crystal grains are substantially uniform with substantially no influence of oxygen defects. On the other hand, if the crystal particles are small, the BET specific surface area becomes large, and the contact area with the electrolyte increases, which tends to be advantageous for high-rate charge / discharge. Yield etc. worsen. To reduce the BET specific surface area, the crystal grains should be enlarged. However, if the crystal grains are too large, satisfactory high-temperature stability cannot be obtained for the reasons described above. Therefore, it is preferable that the average diameter of the crystal particles is 2 μm or less and the BET specific surface area is 1.0 m 2 · g −1 or less.
[0018]
As shown in the present invention, in order to greatly improve the high temperature stability, the chemical composition, that is, the metal element M (M is the IIa group in the second and third periods, IIIb It is important that the half width of the (400) plane of the powder X-ray diffraction is 0.22 ° or less. It is particularly important that the average diameter of the crystal particles by SEM observation is 2 μm or less and the BET specific surface area is 1.0 m 2 · g −1 or less. These make it possible for the first time to obtain sufficient high-temperature stability.
[0019]
The lithium manganese oxide of the present invention is obtained by using electrolytic manganese dioxide as a manganese raw material in a metal salt aqueous solution of M (M is at least one selected from Group IIa, Group IIIb and Group VIII of the second and third periods). It can manufacture by making Mn-M complex oxide slurry manufactured by adding an alkali, stirring, as a raw material. Lithium manganese oxide of the present invention is fired in the atmosphere by adding a lithium raw material thereto or in a high-concentration oxygen atmosphere (including a pure oxygen atmosphere), that is, in an atmosphere having an oxygen concentration of 18 to 100%. Is obtained.
[0020]
In the synthesis of the lithium manganese oxide of the present invention, it is important to use electrolytic manganese dioxide as a manganese raw material. Electrolytic manganese dioxide usually has a large BET specific surface area of about 30 to 40 m 2 / g, which is M (M is at least one selected from Group IIa, Group IIIb and Group VIII of the second and third periods). By stirring in an aqueous metal salt solution, M can be uniformly adsorbed on the surface, and an alkali such as ammonia water can be added to immobilize it on the surface. Stirring may be performed at room temperature or at a high temperature below the boiling point of the aqueous solution. The raw material of the metal element M used for the synthesis may be any water-soluble salt, and examples thereof include nitrates and sulfates. The Mn-M composite oxide slurry produced in this way may be used as it is, but may be used after being dried, or it may be fired, for example, M containing Mn 2 O 3 or Mn 3 O 4. You may use it after making it a lower oxide like this.
[0021]
The lithium raw material used for the synthesis is any compound as long as it is a compound that starts a complexing reaction with manganese oxide at a temperature of 500 ° C. or lower, such as lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium iodide. They may be used, or they may be mixed in a dry manner, or may be slurried or dissolved and mixed in a wet manner. However, in order to improve the mixing property or solubility, the average particle size is 5 μm or less, more preferably 2 μm. It is particularly preferable to use the following lithium raw materials.
[0022]
Firing for obtaining the lithium manganese oxide of the present invention is performed in the air or in a high-concentration oxygen atmosphere (including a pure oxygen atmosphere), that is, in an oxygen atmosphere having an oxygen content of 18% to 100%. Is preferably in the range of 700 ° C. to 950 ° C. At a temperature lower than this, it takes a very long time to sufficiently reduce the BET specific surface area. At a temperature higher than this, the crystal grains tend to grow abnormally. Further, since lithium manganese oxide has the property of releasing and absorbing oxygen at high temperatures, it is more preferable to perform the cooling rate after firing at a rate of 20 ° C. or less per hour in consideration of oxygen absorption.
[0023]
As the negative electrode of the lithium secondary battery of the present invention, a lithium metal, a lithium alloy, or a compound that occludes lithium in advance and can occlude and release lithium can be used.
[0024]
Examples of the lithium alloy include, but are not limited to, the lithium / tin alloy, lithium / aluminum alloy, and lithium / lead alloy.
[0025]
The compound capable of occluding and releasing lithium is not limited to the present invention, and examples thereof include carbon materials such as graphite and graphite, iron oxides, and cobalt oxides.
[0026]
The electrolyte of the lithium secondary battery of the present invention is not particularly limited. For example, carbonates such as prolene carbonate and diethyl carbonate; sulfolanes such as sulfolane and dimethyl sulfoxide; lactones such as γ-butyrolactone; dimethyl sulfoxide A solution in which at least one of lithium salts such as lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and trifluoromethanesulfonic acid is dissolved in at least one organic solvent of Inorganic and organic lithium ion conductive solid electrolytes can be used.
[0027]
Examples are shown below as specific examples of the present invention, but the present invention is not limited to these examples.
[0028]
In addition, the powder X-ray-diffraction measurement in the Example and comparative example of this invention was performed by the method shown below.
[0029]
Powder X-ray diffraction measurement model MXP3 manufactured by Mac Science
Irradiation X-ray Cu Kα ray measurement mode Step scan Scan condition 0.04 ° as 2θ
Measurement time 5 seconds Measurement range 5θ to 80 ° as 2θ
Further, the BET specific surface area was measured by a nitrogen adsorption method, and the average particle diameter was measured by Microtrac.
[0030]
【Example】
[Production of lithium manganese composite oxide]
Example 1
(Synthesis of Li [Mn 1.85 Li 0.05 Mg 0.1 ] O 4 )
As Example 1, Li [Mn 1.85 Li 0.05 Mg 0.1 ] O 4 was performed by the following method.
[0031]
87 g of electrolytic manganese dioxide was added to 1 L of an aqueous solution containing 0.054 mol / L magnesium sulfate and stirred while heating to 80 ° C., and 100 ml of 3 wt% aqueous ammonia was added dropwise over about 2 hours, and the mixture was further stirred for 4 hours. Then, filtration and drying were performed. After baking this at 800 ° C. for 12 hours, a predetermined amount of lithium carbonate having an average particle diameter of 2 μm was mixed in a dry manner and baked at 800 ° C. for 24 hours. The compound obtained from the powder X-ray diffraction measurement has a spinel structure, and SEM observation confirmed that the crystal particles have a regular octahedral shape and are well sized. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0032]
Example 2
(Synthesis of Li [Mn 1.85 Li 0.05 Ni 0.1 ] O 4 )
As Example 2, synthesis of Li [Mn 1.85 Li 0.05 Ni 0.1 ] O 4 was performed by the following method.
[0033]
87 g of electrolytic manganese dioxide was added to 1 liter of 0.054 mol / L nickel sulfate and stirred while heating to 60 ° C., and 100 ml of 3 wt% aqueous ammonia was added dropwise over about 2 hours, and the mixture was further stirred for 4 hours. Then, filtration and drying were performed. The filtrate was confirmed to be colorless and transparent. A predetermined amount of lithium carbonate having an average particle diameter of 2 μm was mixed in a dry manner and baked at 800 ° C. for 24 hours. The compound obtained from the powder X-ray diffraction measurement has a spinel structure, and SEM observation confirmed that the crystal particles have a regular octahedral shape and are well sized. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0034]
Example 3
(Synthesis of Li [Mn 1.80 Li 0.05 Al 0.15 ] O 4 )
As Example 3, Li [Mn 1.80 Li 0.05 Al 0.15 ] O 4 was performed by the following method.
[0035]
87 g of electrolytic manganese dioxide was added to 1 L of an aqueous solution of 0.084 mol / L aluminum sulfate and stirred while heating to 90 ° C., and 100 ml of 3 wt% aqueous ammonia was added dropwise over about 2 hours, and the mixture was further stirred for 4 hours. Then, filtration and drying were performed. After baking this at 900 ° C. for 12 hours, a predetermined amount of lithium carbonate having an average particle diameter of 2 μm was mixed in a dry manner and baked at 900 ° C. for 24 hours. The compound obtained from the powder X-ray diffraction measurement has a spinel structure, and SEM observation confirmed that the crystal particles have a regular octahedral shape and are well sized. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0036]
Example 4
(Synthesis of Li [Mn 1.74 Li 0.03 Al 0.23 ] O 4 )
As Example 4, Li [Mn 1.74 Li 0.03 Al 0.23 ] O 4 was synthesized in the same manner as in Example 3 except that the excess amount of Li and the added amount of Al were changed. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0037]
Example 5
(Synthesis of Li [Mn 1.80 Li 0.05 Fe 0.15 ] O 4 )
As Example 5, Li [Mn 1.80 Li 0.05 Fe 0.15 ] O 4 was performed by the following method.
[0038]
To 1 L of an aqueous solution of iron (II) sulfate 0.084 mol / L, 87 g of electrolytic manganese dioxide was added and stirred at room temperature. At this time, when the stirring was interrupted, the supernatant liquid, which was initially light green of divalent iron, became yellow-brown derived from trivalent manganese or trivalent iron ions after stirring for 1 hour. This is due to the oxidation-reduction reaction between divalent iron and manganese dioxide, and it was considered that iron ions strongly act on the surface of the manganese dioxide particles. While stirring, 100 ml of 3 wt% aqueous ammonia was added dropwise over about 2 hours, followed by further stirring for 4 hours, followed by filtration and drying. The filtrate was colorless and transparent. After calcining this at 800 ° C. for 12 hours, a predetermined amount of lithium carbonate having an average grain size of 2 μm was mixed in a dry manner, and calcined at 850 ° C. for 24 hours. The compound obtained from the powder X-ray diffraction measurement has a spinel structure, and SEM observation confirmed that the crystal particles have a regular octahedral shape and are well sized. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0039]
Example 6
(Synthesis of Li [Mn 1.80 Li 0.05 Mg 0.05 Al 0.10 ] O 4 )
As Example 6, Li [Mn 1.80 Li 0.05 Mg 0.05 Al 0.10 ] O 4 was synthesized in the same manner as in Example 3 except that the Mg addition amount and the Al addition amount were changed. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0040]
Comparative Example 1
As Comparative Example 1, magnesium hydroxide, lithium carbonate, and electrolytic manganese dioxide were weighed so as to have the same composition as in Example 1, and after dry mixing, firing was performed at 800 ° C. for 24 hours, and Li [Mn 1.85 Li 0.05 Mg 0.10 ] O 4 was synthesized. From the SEM observation, the crystal particles were well-developed in the shape of an octahedron, but they were a mixture of coarse particles of 5 μ or more and fine particles of 1 μ or less. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0041]
Comparative Example 2
As Comparative Example 2, aluminum hydroxide, lithium carbonate, and electrolytic manganese dioxide were weighed so as to have the same composition as in Example 6, mixed after dry mixing, and then fired at 900 ° C. for 24 hours to obtain Li [Mn 1.80 Li 0.05 Mg 0.05 Al 0.10 ] O 4 was synthesized. From the SEM observation, the crystal particles had a well-developed regular octahedral shape, but as in Comparative Example 1, coarse particles of 5 μ or more and fine particles of 1 μ or less were mixed. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0042]
Comparative Example 3
As Comparative Example 3, electrolytic manganese dioxide and lithium carbonate were mixed in a dry manner and baked at 900 ° C. for 24 hours to synthesize Li [Mn 1.90 Li 0.10 ] O 4 . From the SEM observation, the crystal particles had a well-developed regular octahedron shape, but as in Comparative Example 1, coarse particles of 5 μ or more and fine particles of 1 μ or less were mixed. Table 1 shows the chemical composition analysis results of the product, the half width of the (400) plane, the crystal particle diameter by SEM observation, and the BET specific surface area.
[0043]
[Table 1]
The lithium manganese composite oxide produced in Examples 1 to 6 and Comparative Examples 1 to 3 was mixed with a conductive agent polytetrafluoroethylene and acetylene black (trade name: TAB-2) in a weight ratio of 2: 1. It mixed so that it might become. 75 mg of the mixture was formed into a pellet shape on a 16 mmφ mesh (SUS316) at a pressure of 1 ton · cm −2 , and then dried under reduced pressure at 200 ° C. for 2 hours.
[0044]
Using this as the positive electrode, using as the negative electrode a piece of lithium cut out from a lithium foil (thickness 0.2 mm), and as the electrolyte solution in a mixed solvent of propylene carbonate and dimethyl carbonate in a volume ratio of 1: 2, A battery having an electrode area of 2 cm 2 was constructed using an organic electrolytic solution in which lithium phosphate was dissolved in a concentration of 1 mol · dm −3 .
[0045]
Table 2 shows capacity retention ratios at 50 ° C. (50th cycle capacity / 10th cycle capacity).
[0046]
[Table 2]
[0047]
【The invention's effect】
As described above, electrolytic manganese dioxide is used as a manganese raw material and stirred in advance in an aqueous metal salt solution of M (M is at least one selected from Group IIa, Group IIIb, and Group VIII of the second and third periods). An Mn-M composite oxide slurry is produced by adding an alkali while adding a lithium raw material to the atmosphere, or in the air or in a high concentration oxygen atmosphere (including a pure oxygen atmosphere), that is, an oxygen concentration atmosphere of 18 to 100%. by firing at medium, the general formula Li [Mn 2-XY Li X M Y] O 4+ δ ( wherein M represents a 2, IIa group of the third period, IIIb group, at least one kind selected from group VIII (0.02 ≦ X ≦ 0.10, 0.05 ≦ Y ≦ 0.30, −0.2 ≦ δ ≦ 0.2), and (400) plane of powder X-ray diffraction by CuKα With a half-value width of 0.22 ° or less A channel-type crystal structure, the lithium manganese composite oxide average size of crystal grains by SEM observation is 2μ or less, and a lithium-manganese composite of BET specific surface area of 1.0 m 2 · g -1 or less of a spinel type crystal structure Oxide can be synthesized, and this is used as the positive electrode active material of lithium secondary batteries, thereby forming a manganese-based lithium secondary battery with greatly improved high-temperature stability that could not be achieved with conventional materials. I found out that I can do it.
Claims (8)
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| EP2214232B1 (en) * | 2007-10-23 | 2012-02-08 | Mitsui Mining & Smelting Co., Ltd | Spinel type lithium-transition metal oxide |
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